The History of Neuroscience in Autobiography

VOLUME 11

The History of Neuroscience in Autobiography

VOLUME 11

Edited by Thomas D. Albright
and Larry R. Squire

Society for Neuroscience

Society for Neuroscience

The Society for Neuroscience publishes works that advance
the understanding of the brain and nervous system.

Copyright © 2020 by the Society for Neuroscience

Published by the Society for Neuroscience
1121 14th Street, NW
Washington, DC 20005
www.sfn.org

All rights reserved. No part of this publication may be reproduced,
stored in a retrieval system, or transmitted, in any form or by any means,
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without the prior permission of the Society for Neuroscience.

Library of Congress Control Number: 96070950

978-0-916110-03-1

Printed in the United States of America

Contents

Previous Contributors

Preface to Volume 1

Preface to Volume 11

Barry J. Everitt

Tamás F. Freund

Uta Frith

Mary B. Kennedy

Eric I. Knudsen

Pierre J. Magistretti

Yasushi Miyashita

Dale Purves

Larry R. Squire

Michael Paul Stryker

Larry W. Swanson

Richard W. Tsien

Index

Previous Contributors

Volume 1

Denise Albe-Fessard

Herbert H. Jasper

Julius Axelrod

Sir Bernard Katz

Peter O. Bishop

Seymour S. Kety

Theodore H. Bullock

Benjamin Libet

Irving T. Diamond

Louis Sokoloff

Robert Galambos

James M. Sprague

Viktor Hamburger

Curt von Euler

Sir Alan L. Hodgkin

John Z. Young

David H. Hubel

Volume 2

Lloyd Beidler

Jerry Lettvin

Arvid Carlsson

Paul MacLean

Donald Grifﬁn

Brenda Milner

Roger Guillemin

Karl Pribram

Ray W. Guillery

Eugene Roberts

Masao Ito

Gunther Stent

Martin Larrabee

Volume 3

Morris H. Aprison

Ainsley Iggo

Brian B. Boycott

Jennifer Lund

Vernon B. Brooks

Edith and Patrick McGeer

Pierre Buser

Edward R. Perl

Hsiang-Tung Chang

Donald B. Tower

Claudio A. Cuello

Patrick D. Wall

Robert W. Doty

Wally Welker

Bernice Grafstein

Volume 4

Per Andersen

Andrew F. Huxley

Mary Bartlett Bunge

JacSue Kehoe

Jan Bures

Edward A. Kravitz

Jean Pierre G. Changeux

James L. McGaugh

William Maxwell (Max) Cowan

Randolf Menzel

John E. Dowling

Mircea Steriade

Oleh Hornykiewicz

Richard F. Thompson

Volume 5

Samuel H. Barondes

Lynn T. Landmesser

Joseph E. Bogen

Rodolfo R. Llinás

Alan Cowey

Alan Peters

David R. Curtis

Martin Raff

Ennio De Renzi

Wilfrid Rall

John S. Edwards

Mark R. Rosenzweig

Mitchell Glickstein

Arnold Bernard Scheibel

Carlton C. Hunt

Gerald Westheimer

Volume 6

Bernard W. Agranoff

Lawrence Kruger

Emilio Bizzi

Susan E. Leeman

Marian Cleeves Diamond

Vernon B. Mountcastle

Charles G. Gross

Shigetada Nakanishi

Richard Held

Solomon H. Snyder

Leslie L. Iversen

Nobuo Suga

Masakazu Konishi

Hans Thoenen

Volume 7

Floyd E. Bloom

Terje Lømo

Joaquín Fuster

Michael M. Merzenich

Michael S. Gazzaniga

John Wilson Moore

Bertil Hille

Robert Y. Moore

Ivan Izquierdo

Michael I. Posner

Edward Jones

Peter H. Schiller

Krešimir Krnjević

Gordon M. Shepherd

Nicole M. Le Douarin

Robert H. Wurtz

Volume 8

Huda Akil

Fernando Nottebohm

Philippe Ascher

Tomaso A. Poggio

Giovanni Berlucchi

Marcus E. Raichle, Sr.

Lily Jan

Pablo Rudomin

Yuh-Nung Jan

Anne Treisman

Bruce Sherman McEwen

Stanley J. Watson, Jr.

Frederick A. Miles

Anne Buckingham Young

Peter M. Milner

Volume 9

David H. Cohen

Nancy Kopell

Yadin Dudai

Margaret Stratford Livingstone

Gerald D. Fischbach

Giacomo Rizzolatti

Sten Grillner

Trevor W. Robbins

Jon Howard Kaas

Wolf Singer

Eric Kandel

David C. Van Essen

Volume 10

Ben A. Barres

Mary Elizabeth Hatten

Anders Björklund

Steven E. Hyman

Thomas J. Carew

Eve Marder

Dennis W. Choi

Roger A. Nicoll

Joseph T. Coyle

S. Murray Sherman

Kjell Fuxe

Douglas G. Stuart

Michael E. Goldberg

Preface to Volume 1

Before the Alfred P. Sloan Foundation series of books began to appear in 1979, the scientific autobiography was a largely unfamiliar genre. One recalls Cajal’s extraordinary Recollections of My Life, translated in English in 1937 and the little gem of autobiography written by Charles Darwin for his grandchildren in 1876. One supposes that this form of scientific writing is scarce because busy scientists would rather continue to work on scientific problems than to indulge in a retrospective exercise using a writing style that is usually outside their scope of experience. Yet, regardless of the nature of one’s own investigative works, the scientific enterprise describes a community of activity and thought in which all scientists share. Indeed, an understanding of the scientific enterprise should in the end be accessible to anyone because it is essentially a human endeavor, full of intensity, purpose, and drama that are universal to human experience.

While writing a full autobiographical text is a formidable undertaking, preparing an autobiographical chapter, which could appear with others in a volume, is perhaps less daunting work and is a project that senior scientists might even find tempting. Indeed, a venture of this kind within the discipline of psychology began in 1930 and is now in eight volumes (A History of Psychology in Autobiography). So it was that during my term as president of the Society for Neuroscience in 1993 to 1994, I developed the idea of collecting autobiographies from senior neuroscientists, who at this period in the history of our discipline are in fact pioneers of neuroscience. Neuroscience is quintessentially interdisciplinary, and careers in neuroscience come from several different cultures, including biology, psychology, and medicine. Accounts of scientific lives in neuroscience hold the promise of being informative and interesting, and they could be a source of inspiration to students. Moreover, personal narratives provide for scientists and nonscientists alike an insight into the nature of scientific work that is simply not available in ordinary scientific writing.

This volume does have a forerunner in neuroscience. In 1975, MIT Press published The Neurosciences: Paths of Discovery, a collection of 30 chapters in commemoration of F. O. Schmitt’s 70th birthday, edited by F. Worden, J. Swazey, and G. Adelman. The contributing neuroscientists, all leaders of their discipline, described the paths of discovery that they had followed in carrying on their work. While writing in the style of the conventional review article, some authors did include a good amount of anecdote, opinion, and personal reflection. A second, similar volume, The Neurosciences: Paths of Discovery II, edited by F. Samson and G. Adelman, appeared in 1992.

In any case, neuroscience writing that is deliberately and primarily autobiographical has not been collected before. This project, The History of Neuroscience in Autobiography, is the first major publishing venture by the Society for Neuroscience after The Journal of Neuroscience. The book project was prepared with the active cooperation of the Committee on the History of Neuroscience, which serves as an editorial board for the project. The first chairperson of the committee was Edward (Ted) Jones; its members were Albert Aguayo, Ted Melnechuk, Gordon Shepherd, and Ken Tyler. This group compiled the names and carried out the deliberations that led to the first round of invitations. In 1995 Larry Swanson succeeded Ted Jones as chair of the committee, and as we go to press with Volume 1 the committee members are Albert Aguayo, Bernice Grafstein, Ted Melnechuk, Dale Purves, and Gordon Shepherd.

In the inaugural volume of the series, we are delighted to be able to present together 17 personal narratives by some of the true pioneers of modern neuroscience. The group includes four Nobel Laureates and 11 members or foreign associates of the National Academy of Sciences, USA. The contributors did their scientific work in the United States, Canada, England, Australia, France, and Sweden. It is difficult to imagine a finer group of scientists with which to inaugurate our autobiographical series. The autobiographical chapters that appear here are printed essentially as submitted by the authors, with only light technical editing. Accordingly, the chapters are the personal perspectives and viewpoints of the authors and do not reflect material or opinion from the Society for Neuroscience.

Preparation of this volume depended critically on the staff of the book’s publisher, the Society for Neuroscience. The correspondence, technical editing, cover design, printing, and marketing have all been coordinated by the Society’s central office, under the superb direction of Diane M. Sullenberger. I thank her and her assistants Stacie M. Lemick (publishing manager) and Danielle L. Culp (desktop publisher) for their dedicated and skillful work on this project, which was carried out in the midst of demands brought by the first in-house years of the Society’s Journal of Neuroscience. I also thank my dear friend Nancy Beang (executive director of the Society for Neuroscience) who from the beginning gave her full enthusiasm to this project.

Larry R. Squire
Del Mar, California
September 1996

Preface to Volume 11

In this eleventh volume of The History of Neuroscience in Autobiography we are pleased to present 12 personal narratives by leaders in our field of science. This stellar group includes seven members of the National Academy of Sciences, three members of the National Academy of Medicine, two members of the Royal Society, as well as two past presidents and the current president of the Society for Neuroscience.

We include in Volume 11 a contribution from Larry Squire, who founded this autobiographical series 26 years ago during his tenure as president of the Society for Neuroscience. From the beginning, the Society leadership understood the importance of documenting the explosive modern growth of a field that brings innovation to medical practice and resonates with a public eager to understand the workings of the brain. Larry’s key insight was that the historical record need not simply reflect the timeline of discoveries; there is also value in recording the “activity and thought in which all scientists share,” for science itself “is essentially a human endeavor, full of intensity, purpose, and drama that are universal to human experience.”

Collectively, the chapters contained in this series do exactly this: They provide a first-hand chronicle of a bold venture in biomedical research, as it has played out in the late 20th and early 21st centuries. Individually, they are treasures, for they are cast in the irresistible and uniquely human form of expression: the story. As such, they connect the dots along paths of scientific discovery, but they also convey the human elements behind those connections, the rich drama and comedy of interpersonal relationships, the sudden flashes of insight, the folly of hubris and the pain of missed opportunities, the beauty of new ideas and the raw excitement of discovery. These are stories populated by imposing and quirky characters, magnified by the lenses of memory and attention. There are tales of brilliance, fantasy, risk, sacrifice, triumph, and camaraderie, but the theme that binds every one of the chapters in this series is success. Thus not only do these chapters entertain in the way that only good stories can, they also offer appealing models and nuanced lessons for success in the human side of science for the next generation of vanguards in our field.

Beginning with publication of the first volume in 1996, Larry Squire’s devotion to this series has yielded an expanding library of autobiographical chapters. Tom Albright joined Larry as coeditor beginning with Volume 9. With the publication of Volume 11, the library of chapters now numbers 155. There are many more great stories in the making, of course, as the field of neuroscience bounds ahead, and we look forward to curating them in these pages.

Beginning with Volume 8 in the series, the Society for Neuroscience assumed full responsibility for this project. Volume 11 was prepared with the advice of the Society’s Publications Committee, which serves as editorial board for the project. With input from this committee, from the Council of the Society for Neuroscience, and many others, names were compiled for Volume 11. Production was overseen by Kelly Newton (director of scientific publications), a role ably held by Suzanne Rosenzweig until her retirement in 2019.

Autobiographical chapters contained in Volume 11 are freely available from the SfN website, along with the 143 chapters that appeared in the first ten volumes of the series. From the SfN homepage, chapters can be accessed either via the “Publications/History of Neuroscience Autobiographical Chapters” menu tabs or via the “About/History of Neuroscience” menu tabs. They can also be accessed directly at this address: https://www.sfn.org/about/history-of-neuroscience/autobiographical-chapters. Hardbound copies of Volume 11 are available for purchase via inquiry to jn@sfn.org.

We hope readers will find Volume 11 as interesting and useful as the earlier volumes.

Thomas D. Albright and Larry R. Squire
Del Mar, California
May 2020

Barry J. Everitt

BORN:

Dagenham, Essex, United Kingdom

February 19, 1946

EDUCATION:

University of Hull, BSc Zoology (1967)

University of Birmingham Medical School PhD (1970)

APPOINTMENTS:

Postdoctoral Research Fellow, University of Birmingham Medical School (1970–1973)

Medical Research Council Traveling Research Fellow, Karolinska Institute, Stockholm (1973–1974)

University Demonstrator, University of Cambridge (1974–1979)

Fellow, Downing College, Cambridge (1974–2003)

University Lecturer, University of Cambridge (1979–1991)

Director of Studies in Medicine, Downing College, Cambridge (1979–1998)

Ciba-Geigy Senior Research Fellow, Karolinska Institutet, Stockholm (1982–1983)

Reader in Neuroscience, University of Cambridge (1991–1997)

Professor of Behavioral Neuroscience, University of Cambridge (1997–2013)

Editor-in-Chief, European Journal of Neuroscience (1997–2008)

Master, Downing College Cambridge (2003–2013)

Emeritus Professor of Behavioral Neuroscience, University of Cambridge (2013–present)

Director of Research, University of Cambridge (2013–present)

Provost, Gates Cambridge Trust, University of Cambridge (2013–present)

HONORS AND AWARDS (SELECTED)

President, British Association for Psychopharmacology (1992–1994)

President, European Brain and Behaviour Society (1998–2000)

President, European Behavioural Pharmacology Society (2003–2005)

Sc.D. University of Cambridge (2004)

Fellow of the Royal Society (elected 2007)

Fellow of the Academy of Medical Sciences (elected 2008)

D.Sc. honoris causa, University of Hull (2009)

D.Sc. honoris causa, University of Birmingham (2010)

European Behavioural Pharmacology Society Distinguished Achievement Award (2011)

American Psychological Association Distinguished Scientific Contribution Award (2011)

Federation of European Neuroscience Societies-European Journal of Neuroscience Award (2012)

British Association for Psychopharmacology Lifetime Achievement Award (2012)

Fondation Ipsen Neuronal Plasticity Prize (2014)

Member of European Molecular Biology Organization (EMBO) (elected 2014)

MD honoris causa, Karolinska Institutet, Stockholm, Sweden (2015)

President, Federation of European Neuroscience Societies (2016–2018)

President, Society for Neuroscience (2019–2020)

Barry Everitt is a behavioral neuroscientist who has an enduring interest in understanding the neural mechanisms of motivation, learning, and memory. His early research focused on the neuroendocrine basis of sexual motivation and behavior in primate and rodent species. He then combined neuroanatomical, neurochemical and behavioral approaches to define the functions of monoaminergic and cholinergic neurotransmitter systems in motivation, learning, and attention.
He made fundamental discoveries on the functions of limbic corticostriatal systems underlying aversive and appetitive behavior through their mediation of Pavlovian and instrumental learning. He formulated, with T. W. Robbins, a theory of drug addiction that proposes a shift from goal-directed to habitual behavior in the development of compulsive drug seeking, reflecting the shifting engagement of the ventral and dorsal striatum and emergent loss of control over behavior by the prefrontal cortex. He has demonstrated the molecular and systems basis of the reconsolidation of addictive drug and fear memories, highlighting the potential of targeting maladaptive memories in the treatment of neuropsychiatric disorders, including addiction.

Barry J. Everitt

Early Years: From School in Dagenham, Essex to University in Hull, Yorkshire: An Education

I was born in Dagenham in the east end of London (southeast Essex) in 1946, soon after my father was demobilized from the Royal Air Force (RAF) at the end of World War II. Three years later my sister Melanie was born and we lived in a new house on a council estate (social housing in United States terminology) that was built to house the many people relocated from London because of the devastation caused during the Blitz. My mother, Winifred, was born in Old Dagenham village and began her working life at age 14 as a maid in service before being recruited to the Sterling machine gun factory in Dagenham as part of the war effort. My father, Fred, was born in Southampton but grew up in Cadoxton, Glamorgan, in South Wales. His father having died when he was very young, he left school at age 13 to work to support his mother after his three older brothers had left home. He came to London to find work during the depression and settled in east London, and then in Dagenham, where he met and married my mother in 1943. He worked until his retirement in the Ford Motor Company, which had built its massive factory on the banks of the river Thames in Dagenham. I had a very loving and supportive, if strict, home life in a social environment in which there was no expectation that anyone would remain in school after the age of 15, which was then the legal leaving age, let alone go to university. Although never having received anything but a basic education, my parents were both very bright and knew that a pathway out of the low expectation working-class environment of Dagenham was through education. I passed the daunting 11-plus examination and went to the South East Essex County Technical High School rather than a traditional grammar school, which taught a range of academic subjects but also technical subjects such as woodwork, metalwork, and architectural drawing—all of which I enjoyed but in none of which did I ever achieve more than basic competence. I regret that I was never particularly studious at school, but I played a lot of sport and was especially good at basketball (which I continued to play into my late 20s) and cricket, which remains a passion. I was constantly in trouble and frequently caned by the headmaster, but was also regarded by my science teachers as bright but underachieving. Not a promising start.

I sat and passed my O (ordinary) level exams at 16, doing well in the sciences, and remained at school in the sixth form (age 16–18) to study zoology, botany, and chemistry at ‘A’ (advanced) level. It was then that I encountered my first significant and influential mentors, and I have come to realize how important such encounters have been at key times during my life and career. As a consequence, I have tried always to take my role as mentor extremely seriously in both research and teaching when interacting with undergraduate and graduate students, as well as postdoctoral researchers spending time in my lab. Vera Clarke (‘Miss Clarke’), the senior sixth-form biology teacher, was a dedicated, kind, and shy spinster who traveled miles across London each day to teach us. She was the first to sit me down and give me a stern talking to about the value of study, and most important of all, she transmitted the excitement and wonder of biological sciences. She was joined by Valerie Singleton who had just graduated from the University of London with a degree in zoology and was doing a temporary teaching job before emigrating to Australia. She was the first person I had met who had just been to university, was only four years older than me, and was a brilliant teacher. She more than anyone made me see the importance of applying to university and, because I was good at it, suggested I study zoology. Alas nobody suggested I might think more widely about what to study at university other than a subject I was good at; had someone suggested to me it would be possible to study medicine, I feel sure I would have tried to do so. As it turned out, I was one of only two or three in a sixth form of more than 100 who applied to and was admitted to university. I went to the relatively new University of Hull in Yorkshire in 1964 to read zoology, also studying organic chemistry and psychology in my first and second years, respectively. I was the first in my family to go to university and, given my family’s financial circumstances, I would never done so had I not received a grant from my local Education Authority. Higher Education grants were then available to everyone but sadly now have been abandoned. As well as my tuition fees, it provided my maintenance of about £300 per year, which was plenty to live on if supplemented with income from the variety of jobs I held during vacation months.

A very traditional zoology course was offered at Hull based on the systematic study of the anatomy and physiology of the animal classes. The department was led by the eccentric, even exotic, Professor Paul ‘Espinasse, an authority on the embryology of feathers, but he was kind and encouraging if occasionally stern (he threw me out of a practical class for incorrectly grasping the lever on a Cambridge rocker microtome). I did not find the first two years of zoology compelling (and played a lot of sport), but in my final year, I took a course on endocrinology, a fairly new subject in the 1960s, taught by Norman Nowell who both stimulated my interest in hypothalamic integration mechanisms and encouraged me to explore a doctoral studentship in neuroendocrinology. I had taken the unusual option of studying psychology in my second year (almost all zoology students read botany) and so had discovered my enduring fascination with motivational theory and hypothalamic mechanisms of motivated behavior. With this combination of interests, I wrote seeking a graduate studentship to the University of Birmingham Medical School where a number of neuroendocrine researchers were working. My application found its way to Joe Herbert who had just been appointed as a lecturer in the Department of Anatomy having completed his doctoral research on primate sexual behavior at the Institute of Psychiatry in London. He invited me for an interview, showed me the very large and impressive primate colony that had been established there through a Ford Foundation grant to Sir Solly Zuckerman, then chair of anatomy. I was accepted as one of his first two doctoral students (Diane Scruton, now Bunsell, was the other) to begin my research project on the neuroendocrine control of sexual behavior in female rhesus monkeys. Diane began with Herbert the research program on the sociosexual behavior of a just-established social group of talapoin monkeys. Herbert was the perfect mentor for me; extremely intelligent, creative, infectiously enthusiastic, and generous, he taught me to think, write, talk about, and enjoy research. I suspect without his influence, my research career would have been very different and may even have petered out at the postdoctoral stage. We remain very close friends. As it turned out, I remained in Birmingham for six years, first as a graduate student and then, after Herbert had left for the University of Cambridge, as a postdoctoral researcher continuing to work on primate sexual behavior funded by the Medical Research Council (MRC).

Graduate and Postdoctoral Behavioral Neuroendocrine Research in Birmingham

Having been drawn into neuroendocrinology by my interest in the regulation of gonadal and adrenal function and the possibility of investigating the integrative functions of the hypothalamus, about which little was known, it came as rather a shock to find myself learning about primate sexual behavior and ethological methods of study. Previous work by Herbert had indicated that androgens might play an important role in regulating sexual receptivity in female primates, not just in males, and that this might explain why they remained sexually receptive throughout the menstrual cycle rather than just in the periovulatory period characterized by estrus in nonprimate mammals. There were also data on women indicating that there was often little or no change in sexual activity following the menopause or after ovariectomy. The main extra-ovarian source of androgens in females is the adrenal glands, and in my doctoral research, I showed that while ovariectomized female rhesus monkeys maintained only on estradiol were sexually receptive, when adrenal function was suppressed by dexamethasone (resulting in a major reduction in plasma testosterone), or following adrenalectomy with corticosteroid replacement, sexual solicitation of male sexual activity was markedly decreased, and females tended to reject attempts by males to mount. This change in sexual motivation was reversed dose-dependently by treatment with testosterone (or androstenedione, which was less potent). My first scientific paper describing these data was published in Nature, a remarkably fortunate beginning (Everitt and Herbert, 1969). My doctoral thesis was examined by Professor Sir Robert Hinde, FRS, the eminent ethologist and director of the Sub-Department of Animal Behaviour in Cambridge. Hinde was a towering intellect, rather intimidating, and my viva was very long; he ended it with the words “I’m afraid we cannot award you your PhD” (at this point, I could taste my heart in my throat) and, after a dramatic pause, continued “but we can recommend most strongly to the degree committee that they do.” I would see this wonderful man regularly over the next 40 years in Cambridge (he died only recently) and he was always supportive, kind, and intellectually uncompromising.

A question arising during my doctoral work concerned the behavioral specificity and site of action of androgens in the female primate brain, at a time when it was beginning to be shown that estradiol and progesterone in female, and testosterone in male, nonprimates exerted their effects on sexual behavior in the ventromedial hypothalamus and medial preoptic area, respectively. The MRC funded a project grant that enabled me to stay as a postdoctoral researcher in Birmingham to investigate the hypothalamic site of action of androgens in female rhesus monkeys. It was a difficult project, and I had to devise the methodology to removably implant testosterone in the brain, but it was successful, and I was able to show that medial preoptic/anterior hypothalamic area implantation of testosterone reinstated receptivity in ovariectomized, estradiol-treated monkeys lacking adrenal androgens (Everitt and Herbert, 1975).

After I left Birmingham, my primate research was interrupted, but it re-started briefly when I moved to Cambridge and resumed working with Herbert and Barry Keverne, who had just arrived from London. We were joined for a year by Michael Baum, who was visiting from MIT, and decided to write a review bringing together the work we had conducted separately and together on the neuroendocrine control of female primate sexual behavior (Baum et al., 1977). This we did within a conceptual framework proposed by the brilliant and pioneering University of Berkeley psychologist, Frank Beach, who made a distinction between proceptivity, receptivity, and attractivity when considering hormonal determinants of sexual interaction in female mammals (Beach, 1976). Our overarching conclusion at that time was that estrogen of ovarian origin facilitated sexual interaction primarily by stimulating the emission of nonbehavioral, mainly olfactory, cues that increased a female’s sexual attractivity, whereas progesterone decreased sexual interaction primarily by reducing sexual attractivity though its vaginal actions. We further concluded that while estrogen may enhance proceptivity by acting in the female’s central nervous system, there was no clear demonstration that it affected the neural mechanisms controlling receptivity. Finally, we concluded that proceptivity and, to a lesser extent, receptivity were modulated by adrenal androgens that may act synergistically with estrogen to facilitate sexual behavior.

When investigating the hypothalamic site of action of testosterone on sexual behavior when still in Birmingham, great interest had begun to emerge in the possibility that monoamine neurotransmitters might in some way mediate the effects of sex steroids on motivational systems in the brain. Bengt Meyerson in Uppsala had shown that some drugs that altered monoamines in the brain profoundly affected sexual behavior in male and female rodents. A visiting postdoctoral researcher from Rhodesia (now Zimbabwe), Peter Gradwell, arrived in Birmingham and along with Herbert and me showed that depleting the brain of 5-hydroxytryptamine (serotonin, 5-HT) with para-chlorophenylalanine increased the proceptivity of estradiol-treated female macaques depleted of androgens, whereas treatment with the 5-HT precursor 5-hydroxytryptophan reduced sexual activity in monkeys not depleted of androgens. Intriguingly, estradiol and testosterone also reduced the turnover of 5-HT in the brain (Gradwell et al., 1975). Of course, it could not be established in these initial experiments whether the effects of sex steroids on behavior were actually mediated by altered serotonin in the brain or whether the steroid and monoamine affected behavioral responses through different mechanisms. It also seemed unlikely that decreasing brain 5-HT had a specific effect on sexual behavior, and of course that proved to be the case. Tragically, Peter Gradwell was murdered in the violence and turmoil that engulfed Rhodesia during the Unilateral Declaration of Independence (UDI) and the establishment of the Republic of Zimbabwe.

A Transforming Postdoctoral Fellowship at the Karolinska Institute in Stockholm: Immersion in Monoamine Research

In the midst of this period of behavioral neuroendocrinology experimentation, the European Science Foundation announced that the first of its winter schools—the European Training Programme in Brain and Behaviour Research—would be held in Zuoz in the Engadine Valley in Switzerland in January 1972. I was fortunate to attend two more, one in 1975 also as a delegate, and the 25th and final one in 1997 as a lecturer. It was themed “Transmission and Behaviour” and could not have been more perfectly timed for me, turning out to be a transformational experience in my life as a researcher. I also began to learn to ski and continued to do so for the next 30 years (but never attained the skill that enabled me to give no thought to the color of the slope that had to be descended having arrived at the top of a ski lift). The lecturers at this first meeting were a who’s who of eminent researchers in these early years of monoamine and chemical transmission research: Jacques Glowinski, Leslie Iversen, Hans Thoenen, Nils-Erik Andén, and Tomas Hökfelt among them. Hökfelt was one of the small group of exceptional researchers from the Amine Group at the Karolinska Institute in Stockholm, including Kjell Fuxe, Urban Ungerstedt, Lars Olson, Gösta Jonsson, and Charlotte Sachs. All had been graduate students of Nils-Åke Hillarp who, with Bengt Falck, had developed the histofluorescence technique to visualize monoamine neurons in the brain (Falck et al., 1962). It was through my discussions with Hökfelt that I realized that what I really wished to immerse myself in during the next phase of my career was neuroscience and especially research on the anatomy of monoamine neural systems, the impact of monoamine transmission on behavior and, at least initially, neuroendocrine integration. I wrote to Hökfelt and Fuxe to ask if they would accept me into the lab as a postdoc, and they said yes. I applied for and was awarded an MRC Traveling Fellowship (a scheme that alas was phased out) to go to Stockholm in October 1973. Having spent my doctorate and first postdoc in Birmingham funded by the MRC, this critical international bridge in my career has meant that I have been funded continuously by the MRC to the present day. I realize that I have been immensely fortunate.

At the Karolinska, my intention was to learn all I could about monoaminergic systems in the brain and how to study them. I was trained to perform the Falck-Hillarp technique with all the joys of freeze-drying brains, reacting them with formaldehyde, and sectioning and then viewing broken sections under ultraviolet (UV) light for hours in the midnight space that was the fluorescence microscopy room. Hökfelt and Fuxe are brilliant neuroanatomists, and it was a joy to learn from them. I was also mentored in neurochemistry by Gösta Jonsson, who taught me how to measure regional monoamine levels and turnover using cation exchange chromatography with fluorescence detection and radioenzymatic assays, and monoamine reuptake in synaptosomes and brain slices. However, this turned out to be a period not only of acquiring monoamine neurobiological skills. Hökfelt and Fuxe were very interested in my earlier findings on 5-HT and sexual behavior in primates and had indicated before my arrival in Stockholm that they wished to collaborate with me to investigate the impact of monoamine transmitters on sexual behavior in rats.

I had never touched a rat, let alone observed and measured the sexual behavior of one, and so I set about acquiring these skills before I left Birmingham. Guided by Fuxe’s neuropharmacological expertise, I began investigating the effects of the rapidly emerging new drugs targeting monoaminergic receptors, as well as monoamine synthesis and reuptake, initially by systemic injection and then by direct manipulation in the brain. The latter involved some of the first behavioral experiments using the recently discovered 5-HT neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), which when infused into the rostral midbrain (while cotreating with catecholamine reuptake inhibitors) selectively depleted the forebrain of 5-HT. These lesion-inducing neurotoxin infusions also caused a buildup of monoamines proximal to the site of neurotoxin injection, enabling the highly transient 5-HT florescence signal to persist under UV light long enough to visualize more accurately the axons of monoamine 5-HT neurons projecting from the raphe nuclei as they merged within the medial forebrain bundle to reach the diencephalon and hypothalamus. This phenomenon had been exploited previously by Urban Ungerstedt in his use of the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) to map catecholamine neurons in the brain. In doing so, he also revealed that nonhomeostatic features of the syndrome of aphagia and adipsia that followed electrolytic lesions of the lateral hypothalamus were largely a consequence of dopamine depletion in the striatum (Ungerstedt, 1971). This remarkable observation opened the way simultaneously to an understanding of the role of dopamine systems in motivation, ingestive behavior, and the motor functions of the striatum, as well as establishing a still-used model of Parkinson’s disease.

It is not unreasonable to suggest that a new era of behavioral neuroscience was beginning, as neuropsychopharmacology now began to emerge as a powerful way to investigate the behavioral functions of monoamine transmitter systems. New drugs with ever-greater specificity were appearing at an incredible rate as big pharma began major discovery programs for new treatments for neurological and neuropsychiatric disorders. It was already becoming apparent that monoamines were key players in these disorders and also potential treatment targets. It rapidly became clear from my own research and that of others that a range of drugs that altered serotonergic, dopaminergic, and noradrenergic transmission had major and dissociable effects on sexual behavior in female rats (Everitt et al., 1975a). I paid careful attention to the distinction between proceptive and receptive behavior in my behavioral analysis of female rats: the distinction between lordosis—the immobile receptive reflex posture—and the extraordinary species-specific proceptive responses of hopping, darting, and ear-wiggling. These appetitive behavioral responses elicited sexual interest and pursuit by males, but they were not often quantified in behavioral experiments. Yet it was clear that proceptive behavior and lordosis, although only displayed at estrus or when ovariectomized females were treated sequentially with estradiol and progesterone, were differentially affected by monoaminergic drugs. For example, dopamine receptor antagonists decreased proceptive behavior but facilitated the immobile lordosis response (Everitt and Fuxe, 1977), and so it became obvious that a distinction had to be made between the general effects of drugs on motor activity and sensory responsiveness to understand any more specific effects on motivational processes. Similarly, while these early experiments showed that sex steroids markedly affected monoamine turnover and reuptake in the hypothalamus, cortex, and brainstem, it was becoming apparent that these hormones were not influencing sexual behavior simply by altering monoamine transmission.

It was increasingly understood that hypothalamic monoamines were involved in neuroendocrine integration (e.g., the role of the tuberoinfundibular dopamine neurons in the control of the release of anterior pituitary hormones). However, it was now clear to me that attempts to understand the behavioral functions of these chemically defined brainstem systems would depend on investigating the way monoamines modulated processing in the many areas of the brain they innervated, not just the hypothalamus. The striatum with its rich dopaminergic innervation was already of growing interest, not least through Ungerstedt’s research. Therefore, the manipulation of monoamine transmission in discrete brain regions would have to be combined with precise behavioral analysis to make further progress. In reality, I was gradually realizing that I had to reconnect with the psychology I had studied as an undergraduate and combine this with my now-complete immersion in, and fascination with, neuroscience. My wonderful postdoctoral time at the Karolinska was life-changing; it enabled me to decide what I was really interested in and enabled me to begin establishing my future career as a behavioral neuroscientist. I shall always be grateful to Tomas Hökfelt and Kjell Fuxe for the inspiring time I spent in Stockholm.

However, I had a major obstacle to overcome which was that my postdoctoral fellowship was quickly coming to an end and political turmoil in the United Kingdom as a result of the oil crisis threatened my future employment. A three-day week was introduced in the United Kingdom in the first quarter of 1974 as part of the government’s response, and the government of Edward Heath lost its majority in the subsequent election. Harold Wilson then led a minority government and, among the inevitable cuts that followed, the lecturer position I had been expecting to take up back in Birmingham was suppressed. I was about to be unemployed and what my wife, our young son, and I were going to do was very uncertain. It just so happened that an Australian academic was briefly visiting Stockholm and was about to set up a new department of anatomy in New South Wales. After some discussion, he offered me a tenure-track position and I began the process of emigration to Australia, visiting the embassy and even having my medical examination. The plan was to return to the United Kingdom briefly, say goodbye to our families and friends and set off for Australia. We were both excited and apprehensive as emigrating had never been in our thoughts before my imminent employment crisis, now only a month or so away.

Appointment to an Academic Post in Cambridge: Behavioral Neuroscience, Sex, and Monoamines

Then, out of the blue, I received news from Joe Herbert, my doctoral supervisor and mentor, that a vacancy for a demonstratorship position had arisen in the Anatomy Department at Cambridge University, where he had been appointed as a lecturer four years earlier. I returned unemployed to the United Kingdom to join my family and live with parents, applied for the position, and was shortlisted, interviewed, and then appointed in November 1974. Sadly, my then wife and I were separated and divorced soon afterward. I began teaching topographical anatomy and other alien subjects in January 1975 and set about reestablishing my research. A demonstratorship in the University of Cambridge was an unusual position (it no longer exists) intended to bridge the gap between doctoral studentship or first postdoctoral position and a lectureship. It was a five-year fixed-term appointment with no guarantee of anything beyond, as upgrading to a lectureship depended on there being a vacancy and was highly competitive. The salary was fixed nonnegotiably at £2,700 per year and there were no annual increments. Yet this small salary allowed me to borrow three times that amount and obtain a mortgage on a two-bedroom house and was just about enough to live on. In Cambridge today, it is necessary to borrow more than 10 times a lecturer’s salary of around £40,000 per year to buy a house and few are able to do so.

So it was that I rejoined Joe Herbert, and the neuroendocrine research group he was establishing in Cambridge. Barry Keverne had joined the lab during my year in Stockholm and was leading research on the sociosexual behavior of the talapoin monkey group that had been brought from Birmingham. We were later joined by Michael Hastings, who worked on circadian and circannual reproductive rhythms. Although I resumed my research on sexual behavior in macaques, it was becoming obvious that this was unsustainable in the department’s poor facilities. I was, in any case, increasingly focused on my research on monoamines and behavior and setting up neurochemistry and neuroanatomy labs with the skills I had acquired in Stockholm.

The Anatomy Department at Cambridge University was a strange and initially hostile place. The great majority of the faculty were research inactive, almost all had Cambridge medical degrees, and they were very suspicious of the three new appointees who had no medical qualification: me, Barry Keverne, and Martin Johnson, a brilliant developmental biologist and also a lifelong friend. However, we had reasonably good experimental space because nobody else was using it, and our neuroendocrine group soon attracted students and visiting researchers. On the back of my experiments in Stockholm that had revealed truly remarkable changes in sexual and aggressive behavior in rats following 5,7-DHT-induced lesions of ascending raphé projections in the midbrain (Everitt et al., 1975b), I began to think about comparing the effects of manipulating each of the major monoamine projections. This work was based on the hypotheses that had emerged from the psychopharmacological data I had collected in Stockholm, as a first attempt to understand their differential contributions to behavioral responses through modulation of diencephalic and forebrain mechanisms. I was increasingly convinced that monoaminergic mechanisms had general, rather than specific, functions (as I and many others had initially thought) and that comparing the effects of manipulating them on the same behaviors or tasks might be revealing.

Early experiments involved infusing 6-OHDA into the dorsal and ventral noradrenergic fiber bundles in the brainstem before they merged in the medial forebrain bundle to course through the lateral hypothalamus. This resulted in noradrenaline depletions from the hypothalamus and other subcortical sites following lesions of the ventral bundle (composed of axons of the medullary noradrenaline cell groups) or from cortical and limbic structures following lesions of the dorsal bundle originating mainly from the locus ceruleus. A visiting research fellow from Gothenburg, Stefan Hansen, together with a final-year undergraduate in Cambridge, Erica Stanfield, working with me on this project showed that ventral bundle lesions left proceptive behavior intact—females still solicited male sexual interest—but impaired the display of lordosis and also prevented pseudopregnancy induced by cervical stimulation (Hansen et al., 1980, 1981). This behavioral and neuroendocrine outcome was interpreted as an impairment in the response to the somatosensory stimulation during coitus that elicited both lordosis and pseudopregnancy. The effects on receptive behavior of noradrenaline depletion were additionally shown to depend on altered striatal dopamine, one of a growing number of demonstrations of noradrenaline-dopamine interactions controlling behavior.

It was around this time that I attended the European Brain and Behaviour Society (EBBS) meeting in Copenhagen in 1976 and first met Trevor Robbins, who was a demonstrator in the Department of Psychology. We had both been working for a couple of years just 25 meters or so apart in adjacent buildings but had never met each other in Cambridge, although I had met and begun collaborating with his former supervisor, Susan Iversen. We soon realized while socializing that we were both interested in and working on monoamines and behavior but from completely different perspectives. We resolved to meet regularly when we returned to Cambridge and this we did, over lunch and at lab talks over the next couple of years. The outcome was the first of many successful joint grant applications funded by the MRC—this first one on comparative functions of cortical and subcortical noradrenergic systems in visual attention and discrimination learning. This enduring connection with Robbins allowed me to re-immerse myself in psychological theory and a completely different approach to studying behavior, and allowed Robbins rapidly to engage with my neuroanatomical and neurochemical expertise. It was the beginning of what is now a 40-year collaboration that was to our great pleasure recognized by the Distinguished Scientific Contribution Award from the American Psychological Association in 2011 that explicitly referred to our collaborative research and mentorship. We began working closely together, but also retained and developed our own research interests and this we both agree has enabled our highly fruitful collaboration to thrive while retaining our individuality. We became and remain the closest of friends.

Over the next several years, I led a sort of parallel research life, beginning and often ending the day running experiments and in discussions with Robbins in the Psychology Department as we pursued our jointly funded work on comparative functions of monoaminergic and later cholinergic neural systems, while in the Department of Anatomy, I was investigating the neural basis of sexual motivation and its modulation by monoamines. The conceptual basis of our joint research evolved from Robbins’s theorizing (inspired by Broadbent’s seminal work on decisions and stress) that the effects on attention, learning, and memory of different central arousal states were dissociably mediated by the noradrenergic, serotoninergic, and dopaminergic systems originating in the brainstem, and later the similarly organized cholinergic basal forebrain projections (Robbins and Everitt, 1982; Everitt and Robbins, 1997). These ideas increasingly influenced my thinking and theorizing about monoaminergic involvement in behavior, mainly sexual behavior at the time, that I had been studying using ethological approaches. I then gradually began to adopt the operant methodologies I was using in collaboration with Robbins in my own investigation of the neural mechanisms underlying sexual motivation, being very much influenced by the great motivational theorists Dalbir Bindra and Jerzy Konorski.

During this period of evolution and transition of my research interests, my personal life was affected by the sudden diagnosis of a malignant melanoma, and I found myself undergoing deep excision surgery and a skin graft. Fortunately, the outcome was good and I was able to escape further screening after several years. A much more positive and exciting event a year or so later was my marriage in 1979 to Jane Sterling, who was in the early stages of her medical career and later embarked on a doctoral degree in virology. We have just celebrated our 40th wedding anniversary. Amidst this period of adaptation and change, Martin Johnson and I completed the first edition of our textbook Essential Reproduction (Johnson and Everitt, 1980), an immersive joint venture borne out of the course we taught together and for which no effective textbook existed; it went through five updates and revisions over the next 20 years. I also returned to Stockholm to work again with Tomas Hökfelt, and Jane came with me to spend time in the dermatology department at the Karolinska Hospital. During this sabbatical year, I acquired the then relatively new technique of immunocytochemistry that enabled even more refined neuroanatomical analysis of monoaminergic neurons, including the coexistence of neuropeptides with the classical transmitters that Hökfelt was studying intensively. My collaboration with Hökfelt on some of this work led to a detailed analysis of the coexistence of neuropeptide-Y in brainstem noradrenergic cell groups (Everitt et al., 1984). During this second period in Stockholm, I met Robert Schwartz who was there collaborating with Fuxe and whose major interest was Huntington’s disease. He introduced me to the remarkable axon-sparing lesions induced by ibotenic acid and other excitotoxins when infused in the brain and their potential use in exploring causal relationships between specific neural structures and behavior. This was to have a significant impact on my future research on the functions of both the hypothalamus and limbic-cortico-striatal systems.

Back in the world of sex research, the medial preoptic area had by now been identified as a key structure underlying sexual behavior in male mammals. However, I was intrigued by the observation that although medial preoptic area lesions prevented copulatory behavior by males, other measures of sexual interest and motivation such as olfactory investigation, pursuit, and even mounting of females were spared. I decided that an objective, quantifiable measure of appetitive, precopulatory behavior, or “sexual motivation” that was independent of sexual performance measures (such as the latency to mount, or intromit or ejaculate) would enable a more fine-grained analysis of the neural mechanisms involved in male sexual behavior. This problem had been faced previously when measuring the motivation for other reinforcers, such as addictive drugs, because attainment of the reinforcer—whether a female or a drug—profoundly affected the performance of the very behavioral responses being taken as measures of motivation. The utilization of second-order schedules of reinforcement by a small group of researchers at the National Institute of Drug Abuse (NIDA) to study drugs as reinforcers (Goldberg, 1973) seemed to offer a possible solution in studies of sexual behavior, although they had never previously been used in this way. The principle is that animals will work for an environmental stimulus, such as a light, that previously had been associated with a reinforcer (or “reward”) through Pavlovian conditioning. This conditioned stimulus (CS) will support appetitive instrumental behavior for long periods of time before the primary reinforcer is obtained, if delivered response-contingently, therefore acting as a conditioned reinforcer.

My idea was that male rats in an operant chamber might respond on a lever for a CS associated with sexual interaction with a receptive female, and this would provide a measure of sexual motivation independent of species-specific copulatory reflexes. The problem was how to do this without having a female present in the operant chamber where lever presses were made, because if she was there, males would simply copulate. Paul Fray, who had been a doctoral student with Susan Iversen, then joined the lab and he was both a very talented psychologist and a highly accomplished technologist. He had already developed a new online computer control language for automatically controlling and recording animal behavior, and now set about constructing an apparatus in which male rats could make lever press responses to gain access to a receptive female. He designed and constructed a compartment above the ceiling of an operant chamber in which a receptive female rat could be placed, the door of which could be automatically opened when a male had completed the instrumental response requirements of a second-order schedule to gain access to her. After overcoming some difficult procedural challenges, we eventually succeeded in training male rats to work for periods of 15 minutes to gain access to a receptive female and then subsequently to interact sexually with her so that both appetitive and performance measures of sexual motivation could be obtained. We also established that contingent presentations of the sex-associated CS were critical if males were to respond; instrumental responses collapsed without the conditioned reinforcing properties of the CS that mediated delays to primary sexual reinforcement (Everitt et al., 1987).

Equipped with this new behavioral procedure, I reinvestigated the role of the medial preoptic area and the effects of testosterone on appetitive and consummatory measures of sexual motivation. A key innovation was to use excitotoxic, axon-sparing lesions of the medial preoptic area induced by infusion of ibotenic acid, which, unlike electrolytic lesions, did not destroy axons en passant or close to the structure of interest. Although a great technical advance then, this, of course, has been surpassed by the exquisite selectivity of optogenetic and chemogenetic techniques that provide a previously unimagined level of specificity in cellular and circuit analysis of brain mechanisms of behavior. The results showed that male rats with medial preoptic area lesions no longer displayed copulatory behavior, confirming earlier data, but they continued to make high levels of instrumental responses to gain access to a receptive female that they then pursued, investigated, and attempted to mount, but could not copulate with (Everitt and Stacey, 1987). This therefore revealed a dissociation in the hypothalamic basis of appetitive and consummatory sexual responses, but left open the question of which neural systems mediated the associative influence on appetitive behavior (Everitt, 1990).

In parallel with these experiments, I had been deploying excitotoxic lesions to begin what has turned out to be still ongoing investigations of amygdala function where electrolytic and other physical lesions massively disrupted pathways between the diencephalon and other temporal lobe structures. It was quickly apparent that excitotoxic amygdala lesions did not result in the classic Klüver-Bucy syndrome that involved “hypersexuality” in some species (that was later shown to depend on a quite different mechanism involving the inferotemporal cortex). A visiting postdoctoral researcher from Bordeaux, Martine Cador, collaborated with me to show that rats with excitotoxic basolateral amygdala lesions showed completely normal, or unaltered, copulatory behavior when interacting with sexually receptive females, but their appetitive instrumental behavior under the second-order schedule was greatly impaired (Everitt et al., 1989). Therefore, we had shown a double dissociation between appetitive and consummatory sexual responses following amygdala and medial preoptic area lesions (Everitt, 1990). In addition, we also revealed an interaction between the basolateral amygdala and nucleus accumbens dopamine transmission in appetitive behavior that was explored more mechanistically in Cador’s parallel study of the neural basis of conditioned reinforcement (Cador et al., 1989).

The Functions of Limbic-Corticostriatal Systems

My research on the neural basis of sexual motivation and behavior was now drawing to a close, save for studies using c-fos cellular imaging to reveal the structures and circuitry activated in males by sexual interaction with females (Baum and Everitt, 1992), and a detailed analysis of the effects of hypothalamic proopiomelanocortin peptides on sexual motivation and performance (Hughes et al., 1990). My interest had shifted to what has been an enduring focus on limbic cortico-striatal mechanisms underlying the influence of learning and memory on motivated behavior. This interest had in part been stimulated by Anne Kelley, who had worked previously with Susan Iversen and was making a brief visit to Cambridge. She had been working with the eminent neuroanatomist Walle Nauta and demonstrated the major projections from the basolateral amygdala to the ventral striatum, especially the nucleus accumbens core and also from the hippocampal formation (ventral subiculum) to the nucleus accumbens shell (Kelley et al., 1982). These neuroanatomical data provided some of the key evidence for the nucleus accumbens as a “limbic-motor interface” in the landmark theoretical paper by Gordon Mogenson and Larry Swanson (Mogenson et al., 1980). I continue to feel great sadness when I think of Anne, a dear friend and an outstanding behavioral neuroscientist, who died so prematurely in 2007.

It was within this neuroanatomical framework that Jane Taylor, an exceptional graduate student working with Robbins, had shown that the effect of stimulant drugs to potentiate the control over behavior by conditioned reinforcers depended on the mesolimbic dopamine system innervating the nucleus accumbens. They used an acquisition of a new response procedure, which isolates the property of a Pavlovian CS to act as a conditioned reinforcer (as the new instrumental response is reinforced only by contingent presentations of the CS and never a primary reinforcer) to show that depletion of dopamine from the nucleus accumbens, but not the caudate-putamen, completely prevented the potentiating effect of intra-accumbens infusions of D-amphetamine on responding with conditioned reinforcement (Taylor and Robbins, 1986). However, nucleus accumbens dopamine depletion did not impair the conditioned reinforcement effect itself. Cador then tested our hypothesis that the association between CS and a water (later food, sex, or drug) reinforcer was formed in the basolateral amygdala, but the potentiation of the control over instrumental behavior by the CS depended on the dopaminergic modulation of its projections to the nucleus accumbens. The results showed that basolateral amygdala lesions prevented or greatly diminished the acquisition of a new response with conditioned reinforcement and thereby prevented or reduced the potentiative effect of intra-accumbens amphetamine (Cador et al., 1989). This finding also informed the interpretation of the effects of basolateral amygdala lesions on the second-order schedule of sexual reinforcement (Everitt, 1990). It was of great interest to us that rats with basolateral amygdala lesions continued to make conditioned approach responses to the source of reinforcement, suggesting that not all Pavlovian CS influences on behavior were disrupted—something we later explored in more detail.

My research interest had by now firmly shifted to dopamine-dependent functions of the ventral and dorsal striatum and the limbic corticostriatal systems involved in motivated behavior, learning, and memory. The realization that a major effect of addictive stimulant drugs is to enhance the control over appetitive behavior by CSs strongly suggested that the future experimental investigation of drug addictive behavior should incorporate an understanding of Pavlovian and instrumental learning and memory mechanisms and their interactions. This has turned out to dominate the research of my laboratory ever since.

Alongside this emerging shift in my area of major interest, Robbins and I continued to investigate the comparative effects of manipulating monoaminergic transmission on attention, impulsivity, and learning and expanded this program to include the basal forebrain cholinergic system. The advent of immunocytochemical visualization of choline-acetyltransferase antibodies enabled this system to be mapped in the brain at a time, more or less, when the “cholinergic hypothesis” of Alzheimer’s disease was formulated, suggesting a link between basal forebrain cholinergic degeneration and memory deficits in the disorder. At the time, there was no neurotoxin specific to cholinergic neurons, so some researchers had made putative lesions of the nucleus basalis of Meynert (nbM) cholinergic neurons by infusing ibotenic acid into the substantia innominata of rats and reported deficits in tests of memory. However, when I looked carefully at the brain following ibotenate infused into this basal forebrain region, I was struck by the relative sparing of magnocellular nbM cholinergic neurons and instead the major destruction of neurons of the dorsal and ventral globus pallidus. The memory impairments following ibotenate-induced basal forebrain lesions therefore seemed very unlikely to be attributable to cholinergic denervation of the cerebral cortex. It so happened that I had begun to explore the effects of other excitotoxic amino acids infused into the basal forebrain, as well as into the amygdala and striatum, and discovered following careful cellular analysis that quisqualic acid and -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) had quite different effects. When infused into the basal forebrain, AMPA much more effectively destroyed cholinergic nbM neurons and relatively spared pallidal neurons. Together with a graduate student, Keith Page, we showed that this differential sensitivity to AMPA excitotoxicity was correlated with GluR4 AMPA receptor subunit (as it was known then) immunoreactivity in magnocellular cholinergic neurons and hence was a serendipitous finding of a more selective, but certainly not specific, cholinergic neurotoxin (Page and Everitt, 1995; Page et al., 1995)

The AMPA-induced lesions of the nbM in rats resulted in a marked reduction in acetylcholine markers in the neocortex, but they did not affect performance in tests of learning and memory in rats, such as the Morris water-maze and passive avoidance (Page et al., 1991). However, they did result in specific deficits in accuracy in a test of visual attentional performance (the five-choice serial reaction-time task, 5CSRTT) and these deficits were dose-dependently reversed by treatment with systemic physostigmine or nicotine (Muir et al., 1992). Intriguingly, analogous improvements in attention were shown in a clinical trial of the anticholinesterase tacrine in patients with Alzheimer’s disease by Barbara Sahakian (who is also Trevor Robbin’s wife and a close friend), thereby providing quite early evidence of successful preclinical-clinical translation and reverse translation. Gráinne McAlonan, who had been a very successful undergraduate medical student undertaking her research project with me and who continued to do her doctoral research in my lab, jointly supervised by Gerry Dawson at the Merck, Sharpe, and Dohme Neuroscience Research Centre (now closed), then began investigating the medial septal and diagonal band of Broca cholinergic neurons that innervate the hippocampal formation and cingulate cortex using AMPA to make relatively selective lesions. She showed that medial septal cholinergic neuron lesions resulted in major reductions in hippocampal acetylcholine, and this did produce delay-dependent deficits in spatial working memory in a delayed non-matching-to-position task in rats, which were partially reversed by low doses of physostigmine (Robbins et al., 1997). This approach was extended to investigate nbM cholinergic function in marmosets in a program led by Angela Roberts that was enabled by the first detailed description of the magnocellular cholinergic neurons and some of their projections in the brain of this species (Everitt et al., 1988).

Although the effects of selective excitotoxic lesions were correlated with cholinergic depletion in innervated structures and task performance was later correlated with acetylcholine release (Dalley et al., 2001), it was clear that further progress in analyzing cholinergic function in the forebrain required a leap forward in chemical specificity of the tools being used (as in the study of catecholamine and serotonin function). This was soon the case with the development of 192-IgG saporin, and the final studies conducted in the lab on forebrain cholinergic function using this chemically specific lesion technique generally confirmed our findings and hypotheses, for example, about cortical acetylcholine and attentional function (McGaughy et al., 2002). Later, sophisticated research by, among others, Martin Sarter (with whom Jill McGaughy had worked before her postdoc in the lab) went on very successfully to deploy selective new tools and to provide a much more detailed and precise understanding of cholinergic basal forebrain function.

My interest in the functions of the amygdala was especially stimulated by our research on the effects of lesions of the basolateral amygdala on appetitive conditioning, because at the time, the great majority of amygdala research was focused on fear conditioning (now much more frequently called threat conditioning, as promoted by Joe LeDoux who suggested researchers should be more cautious about inferring subjective states in animals, a view I share). Indeed, some leading amygdala researchers stated firmly that the amygdala is specialized for processing fear, despite the early fundamental findings published in a landmark paper by a scientific hero of mine, Larry Weiskrantz (Weiskrantz, 1956), showing this could not be the case. However, axon-sparing excitotoxic lesions now offered a significant new and relatively selective tool with which to probe possibly dissociable functions of different amygdaloid nuclei and their associated circuitries. Together with a graduate student, Lawrence Dunn, we already had shown that passive avoidance, conditioned taste aversion, and taste neophobia could be dissociably affected by discrete amygdala and gustatory insular cortex excitotoxic lesions, demonstrating that some effects previously attributed to the amygdala following more gross manipulations were most likely the result of interruption of projections to and from the insular cortex that passed through the medial temporal lobe (Dunn and Everitt, 1988).

Simon Killcross, who had completed a doctorate with Trevor Robbins and joined our Human Frontier Science Programme (HFSP) grant as a postdoc, made the significant discovery of dissociable effects of selective excitotoxic central and basolateral amygdala lesions on two different responses to conditioned threat stimuli within the same task—that is, conditioned suppression (automatic, reflexive) and punishment avoidance (volitional, choice behavior). Rats with lesions of the central nucleus showed a marked attenuation of conditioned suppression of appetitive responses when an aversive CS was presented, but they were still able to direct their actions to avoid further presentations of the aversive CS. In contrast, animals with lesions of the basolateral amygdala were unable to avoid the conditioned aversive CS by their choice behavior, but they showed normal conditioned suppression (Killcross et al., 1997). Thus, animals were both impaired and unimpaired in their conditioned fear behavior depending on the nature of the response to the conditioned threat CS being measured. This was heresy of course, as the dominant serial processing model of amygdala function in conditioned fear required that the CS-unconditioned stimulus (US) association occurred in the basolateral amygdala that relayed this associated information to the central nucleus to effect automatic behavioral (e.g., freezing, suppression), endocrine, and physiological fear responses through its direct projection to hypothalamic and brainstem sites. Such was the dominance of this model that experimental data that did not conform were classed as rogue (one commentary suggested that although our data were interesting, the task we used was complex, so the data should be viewed with suspicion whilst the model itself should not be questioned!).

One conclusion from our study, however, was not that the notion of serial processing within basolateral amygdala-central nucleus circuitry should be rejected as clearly it explained many data, but that some forms of aversive learning did not require basolateral amygdala-central amygdala serial processing. Our results showed that the central amygdala nucleus could mediate some forms of threat conditioning and fear responses in the absence of the basolateral amygdala and vice versa. The results also emphasized that basolateral amygdala outputs to other structures, especially the ventral striatum and prefrontal cortex, should be taken into account when considering associative influences not only on appetitive (as our conditioned reinforcement experiments had shown) but also on aversive behavior. Optogenetic, chemogenetic, and cellular imaging methodologies have now moved the field well beyond the macroscopic analysis of amygdala function that was possible then and have revealed much more precisely the complexities of discrete and seemingly highly specialized amygdala circuits involved in appetitive and aversive behavior, for example, through the work of Patricia Janak, Kay Tye, and Andreas Luthi.

From Anatomy to Experimental Psychology in Cambridge: Pavlovian-Instrumental Interactions and Addiction Research

By the late 1980s to early 1990s, I had made the decision to orient my lab increasingly toward the field of experimental drug addiction research, but I was in impossibly inadequate research space and increasingly isolated in the Department of Anatomy in Cambridge, although still collaborating very successfully with Trevor Robbins in the Department of Experimental Psychology. Following rather intense discussions with the university when I had come very close to accepting a position in another university, it suddenly became possible to move my entire lab and readership to the Department of Experimental Psychology. This would never have been possible without the incredible support of Nick Mackintosh, the preeminent learning theorist and then chair of the department. This enabled Robbins and me, to establish a joint behavioral neuroscience laboratory, having been planning and scheming to do so for more than a decade. The combination of Mackintosh’s negotiating skills and the university’s considerable financial investment eventually delivered both new wet labs and a new animal facility with, finally, specially designed animal behavioral facilities.

As I moved to the Department of Experimental Psychology, which felt very much like coming home, one of those magical moments that can happen during the life of a lab took place in mine with the simultaneous arrival of an exceptional group of graduate students: John Parkinson, Rutsuko Ito, Jeremy Hall, Anastasia Christakou, and Rudolf Cardinal, followed soon afterward by Jonathan Lee and Amy Milton. They helped initiate and progress the research programs on appetitive conditioning and the differential involvement of the amygdala, hippocampus, and prefrontal cortex; their circuit interactions with the ventral and dorsal striatum; and the modulation of these circuits by the dopamine system. It rapidly became clear that manipulations of the basolateral amygdala and central amygdala resulted in dissociable outcomes in appetitive Pavlovian conditioning tasks, as we had seen in aversive tasks (Everitt et al., 2003). For example, John Parkinson and Jeremy Hall showed that central nucleus lesions prevented the acquisition of conditioned Pavlovian approach behavior (more often now called “sign tracking”) (Parkinson et al., 2000b). Patricia Robledo, a postdoc in the lab, had previously shown that similar central amygdala lesions, although not affecting conditioned reinforcement, prevented the potentiating effect of D-amphetamine infused directly into the nucleus accumbens (Robledo et al., 1996). This was quite different than the effects of basolateral amygdala lesions and suggested a functional relationship between the central amygdala and activity of the midbrain dopaminergic (DA) system.

Further analysis revealed that central nucleus, but not basolateral amygdala, lesions prevented Pavlovian-to-instrumental transfer (PIT), the motivational impact of a noncontingently presented reward-associated CS to boost separately trained instrumental responses for that reward (Hall et al., 2001b). The involvement of amygdala subsystems in PIT was later analyzed in greater detail by Bernard Balleine and colleagues who showed that the basolateral and central amygdala mediated specific and general PIT, respectively, with the latter reflecting more general arousal elicited by a motivationally salient CS (Corbit and Balleine, 2005). Michela Gallagher and Peter Holland, then at Duke University, with whom we shared an HFSP grant with Betsy Murray at the National Institutes of Health (NIH), also showed that some Pavlovian-conditioned responses, such as orienting to a food-predictive CS, depended on the central amygdala but not on the basolateral amygdala and that this too involved circuitry linking the central nucleus of the amygdala with DA neurons in the midbrain and thence the striatum (Han et al., 1997).

These investigations of amygdala function emphasized to me something that I believe even more now, which is that a strong learning theory framework and a clear understanding of the psychological processes engaged in behavioral tasks is essential for our understanding of neural circuit function. I feel fortunate to have had Tony Dickinson as a colleague in the department and as a collaborator and friend. He helped to inspire the graduate students and postdocs working in the lab to bring learning theory and behavioral neuroscience closer together, something Robbins and I had been committed to for some time. Rudolf Cardinal was especially concerned to provide a learning theory explanation for the increasing number of dissociable functions of the central and basolateral amygdala (Cardinal et al., 2002). This was a particular challenge for the central nucleus of the amygdala, which generally had been viewed simply as a downstream effector nucleus of the basolateral amygdaloid complex. Even though receiving afferent connections appropriate to support them, no direct evidence suggested that the central amygdala nucleus is itself a site of Pavlovian association as it might, indeed does, receive an already-associated input. Yet it was the case that animals lacking a basolateral amygdala were able to form some kinds of association, the conditioned expression of which was sensitive to central, but not basolateral amygdala, lesions or inactivations, and therefore, the locus of Pavlovian conditioning was unlikely solely to be the lateral and basal amygdala (Cardinal et al., 2002).

Considering the kinds of conditioned responses that seemed to depend on the central amygdala nucleus, our initial analysis led us to suggest that it does form simple CS–unconditioned response (UR; “sensorimotor”) associations that do not depend on a specific US and that are independent of the identity and current motivational value of the US, and therefore, the central amygdala is also unable to support second-order conditioning. We further suggested (Everitt et al., 2000) that the responses subserved by central amygdala-dependent associations especially included the modulation of reflexes organized within the brainstem, including some that might conventionally be regarded as “affective,” such as conditioned suppression, conditioned orienting, and PIT that are disrupted by central but not basolateral amygdala manipulations. We proposed that responses such as conditioned suppression may influence instrumental behavior nonspecifically (i.e., by influencing the ongoing level of all instrumental responses) but are insufficient to modulate instrumental behavior differentially (i.e., affect choice). We further suggested that the basolateral amygdala stores the associations that allow the CS to retrieve the affective or motivational value of its particular US, a form of Pavlovian stimulus–outcome association (Cardinal et al., 2002). This associative information can then, through its major projection to the central amygdala and then to hypothalamic, midbrain, and brainstem targets, control “affective” responses, such as freezing or fear-potentiated startle, and can modulate arousal and attention. The other perhaps major realization from our research was that Pavlovian representations in the basolateral amygdala also can influence appetitive instrumental actions, for example, through projections to the ventral striatum.

Very much related to this analysis of amygdala function was my increasing interest in the striatum, particularly the ventral striatum, because of its connectivity with the amygdala and also with the hippocampus and areas of the prefrontal cortex. The finding that amygdala-dependent conditioned reinforcement was potentiated by DA transmission in the nucleus accumbens confirmed that there are behaviorally important interactions between these structures. This led us to explore in more detail behavioral processes dependent on the nucleus accumbens, informed by the then-recent description of discrete core and shell compartments each with its own relatively specific connections (Jongen-Relo et al., 1994; Groenewegen et al., 1999). Parkinson, Hall, and Cardinal working independently and collaboratively with each other and with me undertook a series of studies to show that the nucleus accumbens is a key site mediating the ability of Pavlovian CSs to invigorate and direct behavior, as measured in sign-tracking, PIT, and conditioned reinforcement tasks, with core and shell subregions being differentially involved in these processes, but that the nucleus accumbens itself is not required for goal-directed instrumental behavior (Cardinal et al., 2002). For example, sign-tracking was shown to depend on the nucleus accumbens core but not the shell (Parkinson et al., 1999). Moreover, in our autoshaping procedure that measured sign-tracking, designed by Tim Bussey, in which visual CSs were presented on a touchscreen that was distant from the location of reward, anterior cingulate cortex connectivity with the nucleus accumbens core was shown to be critical for the development of a discriminated conditioned approach (sign-tracking) (Parkinson et al., 2000a). Thus, we were beginning to define separable and quite specific functions of discrete limbic cortical-nucleus accumbens circuits, having previously shown that disconnecting the basolateral amygdala and nucleus accumbens (the disconnection approach will be discussed more later) impaired the acquisition of conditioned “place” preference (Everitt et al., 1991). (In fact, the commonly used conditioned place preference procedures do not truly measure “place” preference unless specially configured to do so, but instead measure learned preference for often-unspecified specific cues in the conditioning context, as will be discussed further.)

The nucleus accumbens core, but not shell, was then shown to be essential for PIT, the potentiation of instrumental responses for food by a food CS (Hall et al., 2001b). I still regret that having made these initial observations about the involvement of the amygdala and nucleus accumbens in PIT, we did not go further and investigate the neural basis of specific and general PIT (but for good reason, as the lab was increasingly focused on behavior related to drug addiction). However, Balleine, who had earlier worked in Cambridge with Tony Dickinson, did do so and, in an impressive series of experiments, showed that specific PIT depended on basolateral amygdala-nucleus accumbens shell circuitry, while general PIT (which we had been measuring in our experiments) depended on the central amygdala and nucleus accumbens core, likely though their interconnection via midbrain DA neurons (Corbit and Balleine, 2011). Indeed, both PIT and sign-tracking were shown to be markedly affected by manipulations of the mesolimbic DA system innervating the nucleus accumbens (Parkinson et al., 2004), which has since been specified more precisely in the work on sign-tracking by Shelley Flagel and colleagues (Flagel et al., 2011).

In pursuing the different functions subserved by the nucleus accumbens core and shell, John Parkinson and Cella Olmstead, a visiting postdoc from Canada, showed that the potentiative effect of psychostimulants on conditioned reinforcement depended specifically on the nucleus accumbens shell, not the core, whereas conditioned reinforcement required the nucleus accumbens core interacting with the basolateral amygdala (Parkinson et al., 1999). The way in which the Pavlovian-instrumental transfer effects, whether PIT or conditioned reinforcement, mediated by amygdala connectivity with the nucleus accumbens core can be modulated by dopaminergic mechanisms specifically in the nucleus accumbens shell still remains fully to be explained.

One of the features of ventral striatal organization that intrigued me at that time was the then recently observed relative compartmentalization of amygdala and hippocampal (ventral subiculum) afferents to the nucleus accumbens core and shell, respectively. Nathan Selden had earlier shown that the amygdala and hippocampus were differentially required for CS and contextual conditioning, respectively, in an aversive trace conditioning paradigm (Selden et al., 1991). Together with Cyriel Pennartz, with whom Robbins and I had secured a second HFSP collaborative grant, we hypothesized that these, in some sense opposing, functions of amygdala and hippocampus (reflecting the earlier ideas of Alexander Cools) were mediated by differentiated projections to the nucleus accumbens core and shell. Rutsuko Ito, now a postdoc having completed her doctoral research (see next section) undertook these challenging experiments in a task that was painstakingly designed together with Carol Barnes and Bruce McNaughton (who were collaborators within the same HFSP grant). Rats were trained sequentially to acquire discrete CS–sucrose conditioning, followed by spatial context–sucrose conditioning in a uniquely designed place preference apparatus characterized by three topographically identical chambers that were discriminable only on the basis of “place” (i.e., path integration). Selective excitotoxic lesions of the nucleus accumbens shell selectively impaired the acquisition of conditioned place preference (truly “place” preference) and the use of spatial information to retrieve information about a discrete CS, whereas nucleus accumbens core lesions attenuated the acquisition of discrete CS responses (Ito et al., 2008). However, the remarkable finding was that disconnection of the hippocampus from the nucleus accumbens shell using unilateral asymmetric lesions of each structure resulted in a pattern of impairment in place conditioning and context-dependent CS retrieval that was very similar to that produced by bilateral nucleus accumbens shell lesions. These results allowed us to conclude that the nucleus accumbens core and shell subserved distinct associative processes but also that the shell and hippocampal formation were functional components of a limbic corticostriatal network involved in spatial context conditioning (Ito et al., 2008).

Our explorations of ventral striatal function revealing that the nucleus accumbens is a key site mediating the ability of Pavlovian CSs to invigorate and direct behavior took another intriguing and exciting turn when Cardinal showed that when rats were offered the choice of an immediate, small reward or a larger, delayed reward, selective lesions of the nucleus accumbens core severely impaired their ability to choose the delayed reward; in other words, they made impulsive choices (Cardinal et al., 2001). This demonstration that the nucleus accumbens is required for impulse control was to have a major impact on our later research on vulnerability to stimulant addiction (Belin et al., 2008).

Neural and Psychological Mechanisms Underlying Addictive Behavior

Robbins, Dickinson, and I began developing our idea that understanding the neuropsychological basis of addiction to stimulants and other drugs may be enhanced by applying theories of learning developed from the more general study of motivational processes and that this might have implications for future therapeutic strategies in the clinic. Much progress had been made, especially by researchers in the United States where the drug addiction field was and continues to be extremely well supported, in defining the specific targets of addictive drugs in the brain and showing that the dopaminergic innervation of the nucleus accumbens is of major importance in mediating the reinforcing effects of addictive drugs. Moreover, particularly through the work and theorizing of Terry Robinson and Kent Berridge (Robinson and Berridge, 1993), attention was already being paid to Pavlovian conditioning mechanisms and adaptations in the mesolimbic DA system to repeated drug exposure to provide an explanation for drug craving. We instead had the notion that the reinforcing effects of addictive drugs, stimulants in particular, depended not only on their initial molecular and cellular sites of action resulting in increased dopamine transmission in the nucleus accumbens, but also on interactions with the associative information conveyed to the nucleus accumbens by its limbic cortical afferents. We felt that progress in the field required more than even a detailed molecular understanding of how drugs act as reinforcers (or “rewards”), or how CSs associated with drug rewards elicit craving as emphasized in Pavlovian theories of addiction, but not readily amenable to operationalization in non-human species. It seemed to us that the fact that individuals must seek and procure drugs before they can take them was extremely important, yet this was relatively neglected in experimental approaches to addiction and therefore that the neural mechanisms of instrumental learning must also be incorporated into explanations of addictive behavior.

Our new approach relied considerably on Dickinson’s original analyses of conditioning with conventional reinforcers showing that the general concept of instrumental positive reinforcement conflates at least two different processes. The first process is the classic stimulus-response (S-R) mechanism by which reinforcers strengthen an association between the response and the contextual and discriminative stimuli present at the time of reinforcement. Behavior controlled by this process is habitual, elicited by these stimuli, divorced from the value of the outcome and autonomous. By contrast, the second process is cognitive and based on knowledge of the causal relation between the instrumental behavior and reinforcement. When controlled by this process, instrumental behavior takes the form of intentional, goal-directed actions that are performed because an individual knows that these actions give access to the reinforcer or outcome and therefore are dependent on the value of the goal (Everitt et al., 2001). We therefore were heading into new and difficult territory as these concepts had not been applied to the study of drug reinforcers, not least because it involves the practical complication of long-term intravenous drug self-administration, a technique that we had somehow to acquire from scratch under strict United Kingdom Home Office regulatory oversight that is a challenge to this day.

We acquired the intravenous self-administration technique during two visits to the lab by Athina Markou, who had recently completed her doctorate with George Koob at the Scripps Institute and who had exquisite technical skills as well as exceptional theoretical insight into the neuroscience of addiction. Athina and her husband Mark Geyer became close family friends, and together with my wife Jane and daughter Jessica, we later spent a wonderful vacation together in her Greek homeland. Tragically, Athina died in 2016 after four years of coping with extremely challenging treatments for cancer; her loss is still acutely felt.

Robbins, Dickinson, and I were then able to initiate our new experimental approach to understanding drug addiction which took the clinical insight embodied within the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; now DSM-V) criteria for “substance dependence” and sought to decompose and augment this in terms of specified learning and cognitive processes deriving from the rich body of animal learning theory that was in that moment being mapped onto specific neural systems. Our investigation of neurobehavioral constructs related to a psychiatric disorder, avoiding descriptions of behavior in terms of subjective states (such as reward, liking, wanting, or craving) in some sense prefaced the embracing of this approach in the Research Domain Criteria (RDoc) of the NIH. Our overarching hypothesis was that drug addiction can be understood as the aberrant engagement of Pavlovian and instrumental learning processes that underpin drug seeking and drug taking (Everitt et al., 2001). We felt then and continue to think now that the distinction between drug seeking—foraging for drugs over long delays with uncertain outcomes—and drug taking—proximal engagement with and ingestion of a drug—is critically important. In a sense, this is a reexpression of the earlier, widely accepted distinction between appetitive and consummatory behavior. The field of ingestive behavior had already embraced the notion of distinctive and dissociable neural mechanisms engaged in foraging for and ingestion of food rewards, but the addiction field was not yet ready to do so.

Our first project investigated the role of so-called drug cues in drug seeking and relapse focusing on the amygdala and its interactions with the nucleus accumbens core that we had already established as being important for conditioned reinforcement. To do this, my graduate student Mercedes Arroyo, working with Athina Markou, adapted the second-order schedule of reinforcement that I had employed to study sexual motivation, but now with intravenous cocaine as the primary reinforcer. Second-order schedules had of course been used previously to study responses for drugs by researchers at NIDA, but a key difference in our approach was to focus on each daily, extended period of cocaine seeking before any drug infusion, as this offered a way to measure the motivation for a drug uncontaminated by its behavioral effects once self-administered (stimulants like cocaine enhance responding whereas opiates suppress it, confounding motivational measures) (Everitt and Robbins, 2000). We were able to establish that rats would work for 15 minutes or longer making up to 300 responses for a single infusion of cocaine if, and only if, a cocaine-associated CS was presented contingent on responding during this drug-free seeking period. If the CS was not presented, cocaine seeking collapsed (Arroyo et al., 1998). Furthermore, if the dose of cocaine was increased on one day, rats worked harder the next day, whereas if the dose was decreased, they worked less (Markou et al., 1999). This is quite the opposite outcome of increasing or decreasing drug dose in simple drug-taking sessions (under continuous reinforcement schedules of reinforcement) in which regulatory processes dominate as rats titrate their optimal blood levels of cocaine, as importantly shown by Roy Wise (Gerber and Wise, 1989). We then showed that excitotoxic lesions of the basolateral amygdala prevented the acquisition of cue-controlled cocaine seeking, but had no effect on cocaine self-administration (i.e., cocaine reinforcement) (Whitelaw et al., 1996), further emphasizing the distinction between the seeking and taking of drugs. The circuit linking the basolateral amygdala with the nucleus accumbens core is therefore required for conditioned reinforcement and hence also for the acquisition of drug seeking; this we have recently confirmed by specifically inactivating this circuit using Cre-mediated DREADD expression in basolateral amygdala neurons projecting to the core.

As a graduate student, Rutsuko Ito made a series of significant findings when investigating striatal mechanisms in both the acquisition and well-trained performance of cocaine seeking. First, she showed that selective lesions of the nucleus accumbens core greatly impaired the acquisition of cocaine seeking, but had no effect on cocaine self-administration. Selective nucleus accumbens shell lesions had no effect on the acquisition of cocaine self-administration, but instead eliminated the potentiative effect of cocaine on responding for the CS (Ito et al., 2004), which was a further demonstration that the shell is a key site mediating the response-amplifying effects of stimulant drugs. Ito, in collaboration with Jeff Dalley, also used in vivo microdialysis to measure extracellular DA during prolonged sessions of cocaine-seeking behavior in rats that had been well trained over about a two-month period. These experiments led to the initially surprising finding that during one hour of responding maintained by the cocaine-associated CS, there was no increase in dopamine in the nucleus accumbens core or shell; only after cocaine infusion did dopamine increase in both regions, somewhat more in the shell than in the core. Noncontingent, unexpected presentations of the cocaine-associated CS, however, did increase dopamine, but selectively in the nucleus accumbens core (Ito et al., 2000). The most remarkable finding was the marked increase in extracellular DA in the anterior dorsolateral striatum during the hour when rats were responding with conditioned reinforcement and to a level that was as high as that later caused by the cocaine infusion (Ito et al., 2002).

These and other observations led us to propose the overarching hypothesis, presented in a now highly cited review (Everitt and Robbins, 2005), that drug addiction can be seen as the endpoint of a series of transitions from initial drug use, when a drug is voluntarily taken because it has rewarding and other effects, through loss of control over drug seeking that eventually emerges as a compulsive, maladaptive habit elicited and controlled by salient environmental stimuli. We proposed that these transitions depend on interactions between Pavlovian and instrumental learning processes that may be aberrantly engaged through the actions of self-administered, addictive drugs. The progression from voluntary to habitual drug seeking, we hypothesized, was underpinned by a transition from ventral to dorsal striatal mechanisms mediating the Pavlovian-instrumental interactions controlling behavior. However, we further proposed that the compulsive quality of drug seeking in addicted individuals required an additional mechanism of diminished prefrontal cortical control over behavior that is a consequence of chronic drug use. There was already considerable functional imaging evidence for prefrontal cortical hypofunction from studies of humans addicted to drugs, most notably by Nora Volkow and colleagues (Volkow et al., 2004).

I have been extremely fortunate that many exceptionally talented postdoctoral as well as graduate student researchers have come to work in my lab in Cambridge to undertake experimental addiction research and to test these hypotheses across the drugs cocaine, heroin, and alcohol. They are very difficult experiments that require a dedication to understanding addictive behavior and great persistence to make progress. It has been interesting to see how challenging the notion of “compulsive habits” (Everitt et al., 2008), or even habits, has been to some in the field. It has been suggested that this is because it trivializes the problem of addiction that faces society, perhaps because it is too easy to dismiss it as a “bad habit,” which I’ve always found surprising. But when it was suggested to me by an experimental addiction researcher at the end of a talk in Mannheim that “people don’t have habits, so how can they be important in addiction?” it became clear that it would be very difficult for many to accept the notion that the instrumental behavior of drug seeking might, at some point, be something other than the expression of goal-directed motivational responses. It still is.

A challenging aspect of probing the goal-directed or habitual associative structure underlying drug seeking is that: (1) it pertains to preparatory and not consummatory responses, and (2) the key tests of reinforcer devaluation and contingency degradation are not easily applied to addictive drugs, especially when administered intravenously. However, in rats drinking alcohol and also cocaine (which is not the usual mode of cocaine self-administration), reinforcer devaluation induced by postingestion gastric malaise revealed that habitual responding developed more rapidly for both drugs than for a food reinforcer (Dickinson et al., 2002; Miles et al., 2003), suggesting the potentially aberrant engagement of the habit system by addictive drugs. We have taken the shift to anterior dorsolateral striatal control over drug seeking to be a proxy for engagement of the habit system, because it has been well-established from studies of responding for food (where devaluation is much easier to achieve) that this striatal domain is required for habit learning, whereas the posterior dorsomedial striatum is required for goal-directed behavior (Balleine et al., 2009). Louk Vanderschuren, a visiting postdoc, demonstrated that the dorsolateral striatum was causally involved in well-established cocaine seeking by showing that infusions of the DA receptor antagonist, alpha-flupenthixol, into this site dose-dependently decreased the performance, or maintenance, of cocaine seeking measured in our now-routine second-order schedule procedure, whereas similar infusions into the nucleus accumbens at the same stage had no effect (Vanderschuren et al., 2005).

Perhaps one of the most significant breakthroughs came when David Belin joined the lab as a visiting postdoc from Bordeaux; he is now a tenured member of the faculty in Cambridge, a collaborator and close friend. He tackled the conundrum of how ventral and dorsal striatal processes were intertwined and how, if indeed it was the case, dorsal striatal mechanisms could come to exert dominant control over drug-seeking behavior. I had speculated, following Suzanne Haber’s remarkable demonstration of spiraling, serial connectivity between the ventral and dorsal striatum mediated by recurrent connections with midbrain DA neurons (Haber et al., 2000), that this might provide a neural circuit substrate for such functional interactions. Belin, who is a brilliant experimentalist, developed a unique ventral-dorsal striatal disconnection procedure by combining a unilateral lesion of the nucleus accumbens core with a contralateral DA receptor antagonist infusion into the anterior dorsolateral striatum, thus functionally disconnecting the putative circuit bilaterally (Belin and Everitt, 2008). Again adopting the second-order schedule cocaine-seeking task in which we knew the dorsolateral striatum exerted dominant control over this behavior when well established, Belin showed that the disconnection greatly decreased cocaine seeking, yet had no effect at all on responding in a newly acquired, goal-directed task. This remarkable finding gave credence to the functional importance of nucleus accumbens-midbrain DA neuron-dorsal striatal functional connectivity. It gained further support from a collaborative in vivo voltammetry study showing that in a cocaine self-administration setting, the development of dorsal striatal DA transients depended on the integrity of the ipsilateral nucleus accumbens core (Willuhn et al., 2012).

We were now beginning to be able to draw a clearer picture of amygdalo-striatal circuitry mechanisms in cocaine seeking, with the basolateral amygdala-nucleus accumbens core circuit mediating conditioned reinforcement and the acquisition of cocaine seeking and the anterior dorsolateral striatum being required for habitual, well-established cocaine seeking, together with a circuit basis for ventral-dorsal striatal interaction. Jennifer Murray, another talented postdoc experimentalist, made the important observation that dopamine receptor blockade in a different site, the posterior dorsomedial striatum, prevented goal-directed cocaine seeking early in acquisition, but was without effect when well established. By contrast, anterior dorsolateral striatal DA receptor blockade had the opposite pattern of effect, decreasing habitual responding having no effect at an earlier stage—a double dissociation (Murray et al., 2012).

The data presented the conundrum of how the amygdala processing of conditioned reinforcers that support drug seeking could interact with the anterior dorsolateral striatum, a structure to which it does not project. Aude Belin-Rauscent now joined this project with David Belin in Poitiers, France, together with Jenn Murray and me in Cambridge under the auspices of a European Associated Laboratory funded by INSERM and the MRC. Murray combined functional disconnections of basolateral or central amygdala with the dorsolateral striatum in a behavioral study; Belin-Rauscent recorded from medium spiny neurons in the dorsolateral striatum while electrically stimulating the basolateral amygdala to investigate the underlying circuitry (Murray et al., 2015). The data revealed that recruitment of dorsolateral striatum, dopamine-dependent control over cocaine seeking is triggered by the basolateral amygdala via the nucleus accumbens core, while the long-term maintenance of the drug-seeking habit depends instead on the central amygdala interacting with the dorsolateral striatum. Moreover, stimulating basolateral amygdala neurons up- and down-regulated anterior dorsolateral striatum medium spiny neurons by a mechanism that depended on the functional integrity of the nucleus accumbens core. We still do not know for certain, but strongly hypothesize, that this involves the serial connectivity between the nucleus accumbens, midbrain dopamine neurons, and the dorsal striatum. This putative and complex circuitry continues to be investigated in the lab using optogenetic and chemogenetic techniques.

The second-order schedule of reinforcement, capturing as it does the important role of drug cues acting as conditioned reinforcers to enable an individual to mediate delays to drug taking, has served us well as a behavioral approach to studying drug seeking. However, it was apparent early on that a different behavioral procedure was required to enable us to study instrumental processes sensitive to the contingencies between actions (or responses) and outcomes and also to distinguish between drug seeking and drug taking that depend on different psychological as well as neural mechanisms.

A visiting postdoc from Canada, Cella Olmstead, initially took on this challenge with Tony Dickinson and me and established a heterogenous chained schedule of cocaine reinforcement in which seeking responses were spatially and temporally distinct from taking responses. Responses on a seeking lever under a random interval schedule were never reinforced, but gave access to a second, taking lever, responding on which delivered intravenous cocaine. In initial studies, this methodology revealed the complex interplay between regulatory, activating, and reinforcing effects of self-administered cocaine (Olmstead et al., 2000). In an equally fundamental study of heroin seeking and taking, we established that opiate-dependent rats learned about the enhanced incentive value of heroin when in withdrawal only if they had previously had the opportunity to self-administer the drug while in the withdrawal state. This observation showed that heroin engages appetitive motivational mechanisms in the withdrawn state, in contradistinction to theories emphasizing only negative reinforcement, and was an affirmation of Dickinson’s theory of incentive learning applied to the motivation for drugs (Hutcheson et al., 2001).

An especially valuable outcome of investing time and effort in developing an instrumental chained schedule of intravenous drug reinforcement was that it enabled a direct test of our hypothesis that drug seeking becomes habitual when performed over an extended period, becoming resistant to reinforcer devaluation. Because it is difficult, if not impossible, to deploy sensory-specific satiety or gastric malaise to devalue intravenous cocaine as opposed to an orally ingested food or drug reward, our approach was instead to devalue the outcome of seeking responses by extinguishing the taking response. This enabled us to probe the underlying associative structure of seeking: were rats working on the seeking lever to get the opportunity to take drug (i.e., a goal-directed action)? Or was responding a manifestation of stimulus-response learning, independent of the value of the outcome and habitual? Olmstead quickly showed that after limited training, cocaine seeking was indeed goal directed, as extinction of the taking response led to a prompt and significant decrease in seeking responses (Olmstead et al., 2001). The same was true in a sucrose seeking-taking chain. We were beaten to the post, however, in the key test of our hypothesis that after a protracted history of seeking and taking cocaine, seeking would be resistant to the devaluation manipulation. Agustin Zapata in Toni Shippenberg’s lab at NIDA adopted our methodology and replicated our initial demonstration that cocaine seeking was goal-directed after a short drug history (replications in complex behavioral experiments are always reassuring). Importantly, they further showed that cocaine seeking became habitual and resistant to devaluation after protracted training and also that the anterior dorsolateral striatum was critically involved in mediating this transition (Zapata et al., 2010). I am sad to mention here that Toni Shippenberg, a warm and generous friend, died in 2012.

The cocaine seeking-taking chained procedure also gave us the opportunity to develop a model of compulsive drug seeking by unpredictably punishing seeking responses such that animals had to run this risk of danger and punishment to gain access to and respond on the taking lever to receive a cocaine infusion. This seeking-taking punishment task, which in one form or another is now used by a number of labs around the world, was the result of the exceptional work of Yann Pelloux when a postdoc in my lab (Pelloux et al., 2007; Pelloux et al., 2015). I cannot pay sufficient tribute to his dedication and meticulous, patient work that transformed our research and also provided one of its biggest challenges: having to incorporate individual differences in behavior when investigating the neural mechanisms of, and the vulnerability to, compulsive drug seeking in addiction. The major finding by Pelloux was that after a brief cocaine-taking history, all rats ceased seeking cocaine when they contingently and unpredictably were punished in a proportion of trials in a session; they voluntarily abstained. However, after a prolonged history of cocaine exposure, about 80% of rats abstained from seeking cocaine, but 20% persisted despite punishment; in other words, they were compulsive (Pelloux et al., 2007). This observation has been replicated many times both in Cambridge and elsewhere. Because only 20% of each experimental cohort of rats becomes compulsive, exploring its neural basis is very challenging. Nevertheless, Pelloux was able to show that an evolving deficit in forebrain serotonin transmission is causally involved in compulsive cocaine seeking (Pelloux et al., 2012). Sietse Jonkman, another exceptional graduate student and later a postdoc in the lab, showed the importance of an extensive history of cocaine intake in the development of compulsion (Jonkman et al., 2012a) and also that a discrete domain of the anterior dorsolateral striatum was specifically involved in mediating seeking under punishment (Jonkman et al., 2012b).

The seeking-taking-punishment task also has been modified to measure compulsive alcohol seeking by Chiara Giuliano, an exceptionally talented behavioral neuroscientist, to show that in rats with a preference for alcohol, a subpopulation persists in seeking alcohol in the face of punishment and are therefore vulnerable to develop the compulsive alcohol seeking characteristic of alcohol addiction (Giuliano et al., 2018). Even more significantly, she successfully directly tested our key hypothesis that alcohol-seeking habits predict and underpin the emergence of compulsive alcohol seeking in a vulnerable population and that this propensity is associated with engagement of, and an inability to disengage, the anterior dorsolateral striatal control over alcohol seeking (Giuliano et al., 2019). This perhaps is the clearest demonstration of the maladaptive, inflexible nature of compulsive alcohol-seeking habits (Belin et al., 2013) and is a continuing major research topic in the lab.

The observations on differing susceptibility to develop compulsive drug seeking naturally raised the question as to what the neurobehavioral vulnerability trait or traits in addiction might be. My collaborator and friend Jeff Dalley had made the serendipitous discovery that a subpopulation of rats performing the 5CSRTT were impulsive, responding prematurely instead of waiting for stimulus presentations before making a response choice. These high-impulsive rats, while not differing in their propensity to self-administer cocaine, escalated their intake much more than low-impulsive animals. High-impulsive animals also had lower levels of D2/3 DA receptors in the nucleus accumbens that were highly correlated with their impulsivity before any exposure to cocaine (Dalley et al., 2007). When David Belin arrived in the lab from Bordeaux to work with me, having there established the three-criteria model of addiction that also encapsulated the core notion of individual vulnerability to compulsivity (Deroche-Gamonet et al., 2004), he tested the hypothesis that high impulsivity is a predisposing factor in the development of cocaine “addiction,” but most especially compulsivity—the self-administration of cocaine in the face of punishment. The results showed that trait high impulsivity, but not high reactivity to novelty, predicted the emergence of compulsive cocaine self-administration and thereby that impulsivity and its neural basis represent an endophenotype for cocaine addiction (Belin et al., 2008). Karen Ersche, working with Trevor Robbins, subsequently tested this hypothesis in humans, adopting an endophenotype strategy to show that impulsivity is a vulnerability trait in stimulant addiction (Ersche et al., 2010). Daina Economidou, an extremely talented postdoc from Crete further showed that high impulsivity also predicted relapse to cocaine seeking after punishment-induced abstinence in the seeking-taking-punishment task and that the propensity to relapse was decreased by the selective noradrenergic reuptake inhibitor, atomoxetine, suggesting a novel therapeutic approach (Economidou et al., 2009). Tragically, while in a wonderfully productive phase of her research and on the threshold of establishing an independent career, Daina was diagnosed with adenocarcinoma of the lung and died just 18 months later while at home with her family in Nicosia. The study of vulnerability traits predicting compulsivity in cocaine, heroin, and alcohol addiction continues to be a major research direction in the Cambridge lab, using a combination of in vivo imaging, molecular, and circuit tools.

The Search for Treatments to Prevent Relapse to Drug Addiction

I have always believed that the greater the understanding of the neural and psychological mechanisms involved in the compulsive pursuit and use of drugs, the more likely it will be that treatments for addiction will be developed that have a rational basis (Everitt, 2014). There is an enormous unmet clinical need given the devastating impact that addiction has on the lives of individuals, their families, healthcare systems, and society. Sadly, this has always been a Cinderella area in pharmaceutical research, and there is little sign of specific new treatments being developed at present. The approach that I began in the lab was, first, to explore the effects of both new and repurposed drugs as treatments that might decrease drug seeking and relapse in our models.

Our first major success in using this approach was the result of a collaboration with Pierre Sokoloff and Jean-Charles Schwartz in Paris, funded under an EU program, investigating a novel partial agonist at the recently discovered D3 dopamine receptor that they had shown to be enriched in the nucleus accumbens and amygdala. An Italian graduate student, Maria Pilla, joined the lab under this collaboration and showed that this new drug, BP897, selectively reduced cocaine seeking under a second-order schedule of cocaine reinforcement, but had no effect on cocaine self-administration (Pilla et al., 1999). A little later, a full D3 dopamine receptor antagonist was developed by GlaxoSmithKline (GSK) and this we showed had an even more profound and seemingly behaviorally selective effect to reduce cocaine seeking (Di Ciano et al., 2003). Further studies by other groups confirmed this effect of antagonism at the D3 dopamine receptor and also that there were apparently few or no unwanted behavioral effects, for example, on motor activity. A division of GSK in Verona began actively developing this lead and a potentially novel antirelapse treatment for cocaine addiction seemed possible, but alas safety concerns about D3 dopamine receptor antagonists caused GSK to end its program, and to date, there is no sign that this exciting preclinical lead will result in a clinically approved treatment. A salutary lesson.

Another perhaps even more promising lead came from a subsequent collaboration with Ed Bullmore under a GSK academic incubator program in the United Kingdom involving a highly selective µ-opioid receptor antagonist. This compound was revealed to have a remarkable profile of behavioral effects by Chiara Giuliano in a major series of meticulously conducted experiments that showed it dose-dependently and significantly reduced cocaine, heroin, and alcohol seeking as assessed under second-order schedules of reinforcement (Giuliano et al., 2012; Giuliano et al., 2013; Giuliano et al., 2015). It had no apparent unwanted or general behavioral consequences, while in parallel experimental medicine studies, it was shown to be well tolerated and to have promising effects on neural responses to food and alcohol cues (Ziauddeen et al., 2013). Even more promising was that pretreatment with this compound reduced both compulsive alcohol seeking and alcohol drinking (Giuliano et al., 2018). Despite these compelling preclinical data, which are consistent with data on naloxone (a less specific µ-opioid receptor antagonist) in clinical studies of cocaine and alcohol addiction, this putative treatment has not been developed further. Chronic dosing studies, in any case, would be needed in animal models to further assess efficacy, but there seems little reason to embark on such challenging experiments without the promise of further treatment development. The area of addiction therapeutics clearly has a long way to go before we see clinical translation, but there remains potential in repurposing already clinically approved drugs to this end. For example, serotonin-selective reuptake inhibition reduced compulsive cocaine seeking (Pelloux et al., 2012), perhaps through a mechanism not unrelated to its efficacy in obsessive-compulsive disorder and there is evidence that treatment trials are being undertaken.

Memories are Made of This: Fear and Drug Memory Reconsolidation

I was convinced early on that in addition to identifying the distinct neural systems of learning implicated in drug addiction, we also should investigate the underlying memory processes upon which such learning depends. I reasoned that the memory for drug-associated CSs and contexts is made more permanent by repeated consolidation through multiple episodes of drug taking, perhaps exacerbated by the effects of addictive drugs on dopaminergic and other plasticity mechanisms in limbic-corticostriatal circuitry. Relapse, even following protracted withdrawal and abstinence, is a logical consequence of such processing. I speculated that retrieval of drug memories elicits both drug-seeking habits and, in humans, a subjective state of drug craving that can lead to further drug seeking and taking (Everitt, 2014). I had fortunately managed to persuade Kerrie Thomas to join the lab, bringing with her great experience in investigating molecular mechanisms of long-term potentiation, with the specific intention of exploring molecular correlates of Pavlovian associations between CSs and cocaine, and the retrieval of memories elicited by such CSs that subsequently impact cocaine seeking and relapse. Jeremy Hall arrived at this time for the research element of his MD-PhD program, and we decided to begin by using cellular imaging to explore Pavlovian CS and contextual fear conditioning. Our previous work had invoked competitive hippocampal and amygdala mechanisms and, perhaps more important, the experimental conditions for such studies would be much easier to control than conditioning to addictive drug effects. The outcome was not what I had expected, as the experiments on conditioned fear drew us into the completely new area of the reconsolidation and extinction of both conditioned fear and drug memories.

In a specially configured, contextual fear paradigm, the rapid and selective induction of brain-derived neurotrophic factor (BDNF) expression in the hippocampal CA1 region, but not zif268 in CA1 or in the amygdala, was shown to be correlated with contextual fear acquisition (Hall et al., 2000). However, contextual or cued fear memory retrieval was then shown to be associated with increased expression of zif268 in the hippocampus and amygdala, respectively, but with no change in BDNF (Hall et al., 2001a). Retrieval of a cocaine memory on presentation of a CS associated with the drug was also then shown to be correlated with increased zif268 expression in the basolateral amygdala (Thomas and Everitt, 2001). These cellular imaging data suggesting different molecular correlates of learning and retrieval emerged just as Karim Nader at McGill had demonstrated amygdala-dependent fear memory reconsolidation. He showed that protein synthesis inhibition in the amygdala within four hours of retrieval of a fully consolidated CS-fear memory resulted in amnesia—subsequent presentation of the CS no longer elicited a conditioned freezing response. Critically, this effect was memory-reactivation dependent, as amygdala protein synthesis inhibition in the absence of memory reactivation was without effect (Nader et al., 2000). The notion that fully consolidated memories might reenter a labile, or active, state previously had been shown in humans (Misanin et al., 1968), but had not been followed up in any great detail, probably in part because the findings went against the dominant consolidation theory, which asserted that once consolidated, a memory is immutable. Nader’s findings presented the field with compelling evidence that retrieved memories could reenter a labile state and must undergo restabilization, or reconsolidation, in the brain if they are to persist. In the reactivation-dependent labile state, they become vulnerable to disruption by amnestic agents.

Although the very word “reconsolidation” implied that the molecular signaling events occurring during consolidation were in some sense recapitulated at retrieval, our own data on BDNF and zif268 expression led us to hypothesize that the protein products of these genes were dissociably involved in consolidation and reconsolidation, respectively. Kerrie Thomas set about designing antisense oligonucleotide probes to target and knock down the BDNF and zif268 genes at specified times during learning and retrieval when she was in the very latest stage of pregnancy, and indeed completed doing so just before leaving the lab to give birth to her daughter. Jonathan (Joff) Lee, a new graduate student in the lab supervised jointly by Kerrie Thomas and me, undertook our first gene knockdown experiments to test this hypothesis in the contextual fear paradigm painstakingly designed by Jeremy Hall. The results of the experiments were remarkable in showing that the molecular basis of consolidation and reconsolidation are doubly dissociable component processes of memory. Contextual fear memory consolidation required the expression of BDNF, but not the transcription factor Zif268, in the hippocampus, whereas reconsolidation required hippocampal Zif268, but not BDNF, expression (Lee et al., 2004).

Later experiments explored the neurotransmitter mechanisms involved in fear memory reconsolidation. For example, Lee demonstrated the bidirectional modulation of reconsolidation and extinction of a CS-fear memory by an antagonist and agonist at the N-methyl-D-aspartate (NMDA) receptor. He showed that an NMDA receptor antagonist prevented both fear memory reconsolidation and extinction leading to the opposite outcomes of memory loss and memory persistence, respectively. By contrast, the NMDA receptor agonist D-cycloserine enhanced reconsolidation and extinction, leading to the opposite outcomes of fear memory persistence and loss, respectively (Lee et al., 2006). Amy Milton, who was a graduate student and then postdoctoral researcher in the lab and is now a tenured member of faculty, later showed the doubly dissociable involvement of GluN2B- and GluN2A-Containing NMDA receptors in the destabilization and restabilization of a reconsolidating fear memory (Milton et al., 2013).

The seemingly dynamic relationship between reconsolidation, induced by brief memory reactivation induced by presenting a single fear-associated CS, and extinction, induced by repeated or prolonged exposure to the CS, was pursued in more detail by a Royal Society visiting research fellow from Argentina, Emiliano Merlo. Merlo had established in his work on memory in crabs that the calmodulin-dependent protein phosphatase, calcineurin, is specially involved in memory extinction. In an ingenious experiment, rats conditioned to a threat CS were exposed 24 hours later to different “doses” of the CS to induce either reconsolidation (1CS) or extinction (10CS), or to the intermediate numbers of 4 and 7 CS presentations. Increasing the number of CSs induced a proportionate decrease in freezing responses to the CS (extinction) and a gradual increase in basolateral amygdala levels of calcineurin. This newly synthesized calcineurin was then shown to be required for the extinction, but not the reconsolidation, of conditioned fear using a gene knockdown approach (Merlo et al., 2014). Intriguingly, during the transition from reconsolidation to extinction (the 4 and 7 CS presentation conditions), Merlo discovered an insensitive state of the fear memory, one in which NMDA receptor agonist and antagonist drugs were completely ineffective either in modulating calcineurin levels in the basolateral amygdala or in altering the reconsolidation or extinction processes. The demonstration that reconsolidation and extinction are mutually exclusive processes also generated the hypothesis of a previously unknown transitional, or “limbo,” state of the original memory between these two alternative outcomes of fear memory retrieval, when neither process is engaged (Merlo et al., 2014).

With this now firm evidence of fear memory reconsolidation and a demonstration of at least some of the neurochemical and molecular mechanisms involved, the big question that confronted us was whether appetitive, especially addictive drug, memories also undergo reconsolidation following reactivation, and whether they could be disrupted by knocking down zif268 in the basolateral amygdala or by interfering with key neurotransmitter mechanisms. It was immediately obvious that this might not be a trivial question to answer, not least given the major procedural differences between CS-fear and CS-drug conditioning. In typical fear conditioning experiments, only one or two pairings of a CS with shock are needed to establish an enduring fear memory. This is not the case for CS-drug conditioning except in the particular case of conditioned place preference procedures, for which a relatively small number of experimenter-administered drug injections could suffice.

I was convinced, however, that if preventing drug memory reconsolidation was to have any translational potential, it had to be demonstrated in a drug-seeking and -taking setting. Even in our most straightforward drug self-administration procedures, there were some 300 pairings of a CS with a cocaine infusion over the 10 days needed to obtain stable drug self-administration. We knew that the resultant CS arising from these multiple CS-drug pairings could sustain drug seeking under a second-order schedule or could induce relapse. I decided that the first experiment should involve the acquisition of a new response procedure that depended both on conditioned reinforcement and the basolateral amygdala, and where we had shown that cocaine-associated CS presentations increased zif268 expression. Lee, who is an exceptional behavioral neuroscientist, took on this challenge and trained rats to make nose-poke responses for intravenous cocaine infusions over 10 days, and then later exposed them to cocaine CSs alone to reactivate the cocaine memory (Lee et al., 2005). The problem was that we had no idea how many CS presentations would be required to reactivate the memory, but not initiate extinction processes. We began by adopting an informal 10% rule; if there had been 10 days of 30 cocaine infusions and pairings with a CS each time, meaning 300 discrete CS-cocaine conditioning sessions, then reactivation would involve 30 CS unreinforced presentations. This fortunately turned out to be effective. Cocaine memory reactivation was performed in conjunction with zif268 knockdown in the basolateral amygdala, with the same antisense oligonucleotide infusion in the absence of memory reactivation serving as a control. The rats then entered the all-important test phase during which we measured the efficacy of the cocaine CS to support the acquisition of a new instrumental response, the canonical test of its conditioned reinforcing property. Rather dramatically, we showed that the cocaine-associated CS could no longer act as a conditioned reinforcer and the knockdown rats did not acquire the new instrumental response (Lee et al., 2005). We then applied the zif268 knockdown in the amygdala at drug memory reactivation to show that it completely prevented the ability of a cocaine-associated CS to support cocaine seeking under a second-order schedule of reinforcement (Lee et al., 2005).

Therefore, we had shown in these experiments both that appetitive, drug-associated memories underwent reconsolidation and that preventing reconsolidation greatly diminished or prevented the effects of the drug CS to influence drug-seeking behavior subsequently, a finding that surely suggested translational potential. Amy Milton went on to demonstrate the involvement of both NMDA and ß-adrenoceptors in cocaine and alcohol memory reconsolidation, also linking the NMDA receptor to zif268 expression in the basolateral amygdala at cocaine memory reactivation (Milton et al., 2008b; Milton et al., 2008a; Schramm et al., 2016). Finally, Kim Hellemans, a visiting postdoc from Canada, showed that opiate conditioned withdrawal memories also underwent memory reactivation-dependent reconsolidation, suggesting that withdrawal memories also might be targeted in a treatment setting (Hellemans et al., 2006).

I am pleased that there has been some realization of the translational potential of this basic behavioral neuroscience research on memory reconsolidation to the clinic. Although the early promise of positive results in the treatment of post-traumatic stress disorder by reactivating traumatic memories under ß-propanolol treatment have not been followed by fully controlled trials, Merel Kindt has shown the extremely successful treatment of severe spider phobia following a single treatment with ß-propranolol at the time of phobic memory reactivation (Soeter and Kindt, 2015). As was always to be expected, successfully applying this approach to drug memories has been much more difficult, but even here, there have been signs of success in the treatment of nicotine and alcohol addiction (Xue et al., 2017; Das et al., 2019). The big challenge has always been and remains defining the precise conditions for memory reactivation that are sufficient to return the memory to a labile state, when amnestic agents can be used effectively, while not engaging extinction mechanisms (when an amnestic treatment actually will have the opposite outcome of memory persistence), or placing the memory in a “limbo” state in which it is impervious to any amnestic treatment. Discovering a biomarker of memory destabilization obviously would be of great utility, but to date, it remains elusive.

Some Final and More Personal Thoughts

Before being invited to contribute this chapter, I had not planned to reflect on my life and my more than 50 years of research in this way. I have enjoyed the opportunity to do so, not least because it has enabled me to reconnect in memory with many people who have had an impact on my life in research. I have been intrigued that many of the questions that interested me when I began my career continue to do so now. Although the detail has changed, my engrossing interest in the behavioral neuroscience of motivation, learning, and memory has been consistent throughout. I have referred to the irreplaceable importance of mentors at key moments in my life and also my interactions with graduate students, postdoctoral researchers, and collaborators, many of whom quite naturally became friends, really good friends who I know I could always turn to. Surely, a privilege of our academic research careers is that we encounter other researchers, both in our laboratories and also at meetings, to discover that we have more in common than just an academic interest, and we establish friendships. That is really rather special.

I was fortunate to have been appointed to an academic post at a great university at just the right time. I had always thought from my time as a graduate student that a career combining teaching and research would be optimal for me, and so it has turned out to be. I have loved the combination of undergraduate teaching, graduate mentorship, and research in a laboratory that has grown, and I have been very fortunate to have had many wonderful young researchers choosing to spend time in it. I was especially happy to have been promoted to professor at the same time as my close friend and collaborator in research, Trevor Robbins; we have shared much as well as supported each other as individuals throughout the past 40 years.

I have also done things during my career that were not planned and that are still genuinely surprising to me. These include playing an active role in the scientific societies I joined and that in some sense had sustained me in my early career. I found this to be very rewarding as well as, I hope, being of value to my colleagues around the world. I was extremely surprised to be nominated and then elected as president of the Federation of European Neuroscience Societies (FENS), an organization that I had helped to establish in 1998 and then had been privileged to lead during its 20th-anniversary year, culminating in an exceptional FENS Forum in Berlin in 2018. If that was not enough, in fact too much, for someone late in their career, being nominated and then elected as president of the Society for Neuroscience (SfN) in its 50th-anniversary year is something I still find to be frankly astonishing. I previously had served SfN as its first program chair from outside the United States, and in other volunteer roles, and am now proud to be its first president from outside North America. As I write this memoir, I am in the first third of my term, and while I find it extremely engrossing and enjoyable, it is also challenging not least because the world is in the accelerating phase of a coronavirus pandemic. The neuroscience discipline, the way that neuroscience research is funded, and the way scientific findings are published and disseminated are in a moment of great change.

In a quite different domain of my life in Cambridge, I was elected Master of Downing College in 2003, having been a fellow of the college since 1976 and the Director of Studies in Medicine for 20 years. Serving in this educational leadership role was never something I dreamed was possible for someone who grew up on a council estate in Dagenham, was not distinguished at school, and was not educated at either Cambridge or Oxford, where at least I would have grown to understand what collegiate education was all about. Living as a family with my wife Jane and daughter Jessica in the beautiful Georgian Master’s Lodge in the heart of this elegant college in the middle of Cambridge was a wonderful experience (and great for sleepovers of my daughter’s friends after late nights on the town). This role provided a special opportunity to engage with undergraduate and graduate students in a unique and supportive way at an important time in their lives. While living there, Jessica successfully navigated both school and university, graduating with distinction in psychology from Oxford University and then with a master’s degree from London University; she is now forging her career in Sydney, Australia. Jane has enjoyed a very successful career as a clinical dermatologist and molecular virologist, and she too is now serving her discipline as president of the Dermatology Section of the Royal Society of Medicine. My son Alex is a dedicated consultant neurologist and epileptologist at a major London teaching hospital and his three children, our grandchildren, are making their ways through school and university. Family, career, outside fulfilment, and enjoyment are always difficult to keep in balance, and this is as true now as it was in the 1960s when I was a graduate student. I have been quite fortunate to have received recognition of my contributions to research and scholarship. I have been equally fortunate to have worked with so many exceptional colleagues. I have been even more fortunate to have a wonderful family.

Acknowledgments

I would like to thank Tom Albright and Larry Squire for inviting me to contribute to The History of Neuroscience in Autobiography. I am so grateful to my mentors, but especially to Joe Herbert who rattled my cage at a critical moment and set me off on my academic career. It has been extremely gratifying to share a significant portion of my research life and an enduring friendship with Trevor Robbins. I will eternally be grateful to the many undergraduate and graduate students and postdoctoral researchers who have spent time in my laboratory and, in particular, David Belin for his immense contribution and for his friendship. In trying to present a coherent and relatively accurate time frame in my narrative, I have not been able to mention all of the individual contributions of many members of the lab, but I hope they know me well enough to realize that I truly appreciate everything that they have done. I am always thrilled to hear of the successes they have enjoyed in their careers. Finally, I would like to thank my wife Jane, daughter Jessica, and son Alex for their support and their love.

Selected Bibliography

Arroyo M, Markou A, Robbins TW, Everitt BJ (1998) Acquisition, maintenance and reinstatement of intravenous cocaine self-administration under a second-order schedule of reinforcement in rats: effects of conditioned cues and continuous access to cocaine. Psychopharmacology (Berl). 140: 331–44.

Balleine B, Liljeholm M, Ostlund S (2009) The integrative function of the basal ganglia in instrumental conditioning. Behav Brain Res. 199: 43–52.

Baum M, Everitt B, Herbert J, Keverne E (1977) Hormonal basis of proceptivity and receptivity in female primates. Arch Sex Behav. 6: 173–92.

Baum MJ, Everitt BJ (1992) Increased expression of c-fos in the medial preoptic area after mating in male rats: role of afferent inputs from the medial amygdala and midbrain central tegmental field. Neuroscience. 50: 627–46.

Beach FA (1976) Sexual attractivity, proceptivity, and receptivity in female mammals. Horm Behav 7: 105–38.

Belin D, Everitt BJ (2008) Cocaine seeking habits depend upon dopamine-dependent serial connectivity linking the ventral with the dorsal striatum. Neuron. 57: 432–41.

Belin D, Belin-Rauscent A, Murray JE, Everitt BJ (2013) Addiction: failure of control over maladaptive incentive habits. Curr Opin Neurobiol. 23: 564–572.

Belin D, Mar AC, Dalley JW, Robbins TW, Everitt BJ (2008) High impulsivity predicts the switch to compulsive cocaine-taking. Science. 320: 1352–55.

Cador M, Robbins TW, Everitt BJ (1989) Involvement of the amygdala in stimulus-reward associations: interaction with the ventral striatum. Neuroscience. 30: 77–86.

Cardinal R, Parkinson JA, Hall J, Everitt BJ (2002) Emotion and motivation: the role of the amygdala, ventral striatum, and prefrontal cortex. Neurosci Biobehav Rev. 26(3): 321–52.

Cardinal RN, Pennicott DR, Sugathapala CL, Robbins TW, Everitt BJ (2001) Impulsive choice induced in rats by lesions of the nucleus accumbens core. Science. 292: 2499–501.

Corbit L, Balleine B (2011) The general and outcome-specific forms of Pavlovian-instrumental transfer are differentially mediated by the nucleus accumbens core and shell. J Neurosci. 31: 11786–94.

Corbit LH, Balleine B (2005) Double dissociation of basolateral and central amygdala lesions on the general and outcome-specific forms of pavlovian-instrumental transfer. J Neurosci. 25: 962–70.

Dalley J, McGaughy J, O’Connell M, Cardinal R, Levita L, Robbins T (2001) Distinct changes in cortical acetylcholine and noradrenaline efflux during contingent and noncontingent performance of a visual attentional task. J Neurosci. 21: 4908–14.

Dalley JW, Fryer TD, Brichard L, Robinson ES, Theobald DE, Laane K, Pena Y, Murphy ER, Shah Y, Probst K, Abakumova I, Aigbirhio FI, Richards HK, Hong Y, Baron JC, Everitt BJ, Robbins TW (2007) Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement. Science. 315: 1267–70.

Das RK, Gale G, Walsh K, Hennessy VE, Iskandar G, Mordecai LA, Brandner B, Kindt M, Curran HV, Kamboj SK (2019) Ketamine can reduce harmful drinking by pharmacologically rewriting drinking memories. Nat Commun. 10: 5187.

Deroche-Gamonet V, Belin D, Piazza PV (2004) Evidence for addiction-like behavior in the rat. Science. 305: 1014–17.

Di Ciano P, Underwood R, Hagan J, Everitt B (2003) Attenuation of cue-controlled cocaine-seeking by a selective D3 dopamine receptor antagonist SB-277011-A. Neuropschopharmacology. 28: 329–38.

Dickinson A, Wood N, Smith J (2002) Alcohol seeking by rats: action or habit? J Exper Psychol Sec B. 55: 331–48.

Dunn LT, Everitt BJ (1988) Double dissociations of the effects of amygdala and insular cortex lesions on conditioned taste aversion, passive avoidance, and neophobia in the rat using the excitotoxin ibotenic acid. Behav Neurosci 102: 3–23.

Economidou D, Pelloux Y, Robbins TW, Dalley JW, Everitt BJ (2009) High impulsivity predicts relapse to cocaine-seeking after punishment-induced abstinence. Biol Psych. 65(10): 851–56.

Ersche K, Turton A, Pradhan S, Bullmore E, Robbins T (2010) Drug addiction endophenotypes: impulsive versus sensation-seeking personality traits. Biol Psych. 68(8): 770–73.

Everitt B, Herbert J (1969) Adrenal glands and sexual receptivity in female rhesus monkeys. Nature. 222: 1065–66.

Everitt B, Herbert J (1975) The effects of implanting testosterone propionate into the central nervous system on the sexual behaviour of adrenalectomised female rhesus monkeys. Brain Res. 86: 109–20.

Everitt B, Fuxe K (1977) Dopamine and sexual behaviour in female rats. Effects of dopamine receptor agonists and sulpiride. Neurosci Lett. 4: 209–13.

Everitt B, Fuxe K, Hokfelt F, Jonsson G (1975a) Role of monoamines in the control by hormones of sexual receptivity in the female rat. J Comp Physiol Psychol. 89: 556–72.

Everitt B, Fray P, Kostarczyk E, Taylor S, Stacey P (1987) Studies of instrumental behavior with sexual reinforcement in male rats (Rattus norvegicus): I. Control by brief visual stimuli paired with a receptive female. J Comp Psychol. 101: 395–406.

Everitt B, Cardinal R, Hall J, Parkinson J, Robbins T (2000) Differential involvement of amygdala subsystems in appetitive conditioning and drug addiction. In: The amygdala: a functional analysis (Aggleton J, ed.), pp. 353–90. New York: Oxford University Press.

Everitt B, Hokfelt T, Terenius L, Tatemoto K, Mutt V, Goldstein M (1984) Differential co-existence of neuropeptide Y (NPY)-like immunoreactivity with catecholamines in the central nervous system of the rat. Neuroscience. 11: 443–62.

Everitt BJ (1990) Sexual motivation: a neural and behavioural analysis of the mechanisms underlying appetitive and copulatory responses of male rats. Neurosci Biobehav Rev. 14: 217–32.

Everitt BJ (2014) Neural and psychological mechanisms underlying compulsive drug seeking habits and drug memories--indications for novel treatments of addiction. Eur J Neurosci. 40: 2163–82.

Everitt BJ, Stacey P (1987) Studies of instrumental behavior with sexual reinforcement in male rats (Rattus norvegicus): II. Effects of preoptic area lesions, castration, and testosterone. J Comp Psychol. 101: 407–19.

Everitt BJ, Robbins TW (1997) Central cholinergic systems and cognition. Ann Rev Psychol. 48: 649–84.

Everitt BJ, Robbins TW (2000) Second-order schedules of drug reinforcement in rats and monkeys: measurement of reinforcing efficacy and drug-seeking behaviour. Psychopharmacology. 153: 17–30.

Everitt BJ, Robbins TW (2005) Neural systems of reinforcement for drug addiction: from actions to habits to compulsion. Nat Neurosci. 8: 1481–89.

Everitt BJ, Fuxe K, Hökfelt T (1975b) Serotonin, catecholamines and sexual receptivity of female rats: pharmacological findings. J Pharmacol (Paris). 6: 269–76.

Everitt BJ, Cador M, Robbins TW (1989) Interactions between the amygdala and ventral striatum in stimulus-reward associations: studies using a second-order schedule of sexual reinforcement. Neuroscience. 30: 63–75.

Everitt BJ, Dickinson A, Robbins TW (2001) The neuropsychological basis of addictive behaviour. Brain Res Rev. 36(2–3): 129–38.

Everitt BJ, Morris KA, O’Brien A, Robbins TW (1991) The basolateral amygdala-ventral striatal system and conditioned place preference: further evidence of limbic-striatal interactions underlying reward-related processes. Neuroscience. 42: 1–18.

Everitt BJ, Cardinal RN, Parkinson JA, Robbins TW (2003) Appetitive behavior impact of amygdala-dependent mechanisms of emotional learning. Ann. NYAS. 985: 233–50.

Everitt BJ, Sirkia TE, Roberts AC, Jones GH, Robbins TW (1988) Distribution and some projections of cholinergic neurons in the brain of the common marmoset, Callithrix jacchus. J Comp Neurol. 271: 533–58.

Everitt BJ, Belin D, Economidou D, Pelloux Y, Dalley JW, Robbins TW (2008) Review. Neural mechanisms underlying the vulnerability to develop compulsive drug-seeking habits and addiction. Philos Trans R Soc Lond B Biol Sci. 363: 3125–35.

Falck B, Hillarp NA, Thieme G, Torp A (1962) Fluorescence of catechol amines and related compounds condensed with formaldehyde. J Histochem Cytochem 10: 348–54.

Flagel S, Clark J, Robinson T, Mayo L, Czuj A, Willuhn I, Akers C, Clinton S, Phillips P, Akil H (2011) A selective role for dopamine in stimulus-reward learning. Nature. 469: 53–57.

Gerber GJ, Wise RA (1989) Pharmacological regulation of intravenous cocaine and heroin self-administration in rats: a variable dose paradigm. Pharmacol Biochem Behav. 32: 527–31.

Giuliano C, Belin D, Everitt BJ (2019) Compulsive alcohol seeking results from a failure to disengage dorsolateral striatal control over behavior. J Neurosci. 39: 1744–54.

Giuliano C, Robbins TW, Nathan PJ, Bullmore ET, Everitt BJ (2012) Inhibition of opioid transmission at the mu-opioid receptor prevents both food seeking and binge-like eating. Neuropsychopharmacology. 37: 2643–52.

Giuliano C, Robbins TW, Wille DR, Bullmore ET, Everitt BJ (2013) Attenuation of cocaine and heroin seeking by mu-opioid receptor antagonism. Psychopharmacology (Berl). 227: 137–47.

Giuliano C, Goodlett CR, Economidou D, Garcia-Pardo MP, Belin D, Robbins TW, Bullmore ET, Everitt BJ (2015) The novel mu-opioid receptor antagonist GSK1521498 decreases both alcohol seeking and drinking: evidence from a new preclinical model of alcohol seeking. Neuropsychopharmacology. 40: 2981–92.

Giuliano C, Pena-Oliver Y, Goodlett CR, Cardinal RN, Robbins TW, Bullmore ET, Belin D, Everitt BJ (2018) Evidence for a long-lasting compulsive alcohol seeking phenotype in rats. Neuropsychopharmacology. 43: 728–38.

Goldberg SR (1973) Comparable behavior maintained under fixed-ratio and second-order schedules of food presentation, cocaine injection or d-amphetamine injection in the squirrel monkey. J Pharmacol Exper Therap. 186: 18–30.

Gradwell P, Everitt B, Herbert J (1975) 5-hydroxytryptamine in the central nervous system and sexual receptivity of female rhesus monkeys. Brain Res. 88: 281–93.

Groenewegen H, Wright C, Beijer A, Voorn P (1999) Convergence and segregation of ventral striatal inputs and outputs. Ann NYAS 877: 49–63.

Haber S, Fudge J, McFarland N (2000) Striatonigrostriatal pathways in primates form an ascending spiral from the shell to the dorsolateral striatum. J Neurosci. 20: 2369–82.

Hall J, Thomas K, Everitt B (2000) Rapid and selective induction of BDNF expression in the hippocampus during contextual learning. Nat Neurosci. 3: 533–35.

Hall J, Thomas K, Everitt B (2001a) Cellular imaging of zif268 expression in the hippocampus and amygdala during contextual and cued fear memory retrieval: selective activation of hippocampal CA1 neurons during the recall of contextual memories. J Neurosci. 21(6): 2186–93.

Hall J, Parkinson JA, Connor TM, Dickinson A (2001b) Involvement of the central nucleus of the amygdala and nucleus accumbens core in mediating Pavlovian influences on instrumental behaviour. Eur J Neurosci. 13: 1984–92.

Han JS, McMahan RW, Holland P, Gallagher M (1997) The role of an amygdalo-nigrostriatal pathway in associative learning. J Neurosci. 17: 3913–19.

Hansen S, Stanfield E, Everitt B (1980) The role of ventral bundle noradrenergic neurones in sensory components of sexual behaviour and coitus-induced pseudopregnancy. Nature 286: 152–54.

Hansen S, Stanfield E, Everitt B (1981) The effects of lesions of lateral tegmental noradrenergic neurons on components of sexual behavior and pseudopregnancy in female rats. Neuroscience. 6: 1105–17.

Hellemans KG, Everitt BJ, Lee JL (2006) Disrupting reconsolidation of conditioned withdrawal memories in the basolateral amygdala reduces suppression of heroin seeking in rats. J Neurosci. 26: 12694–99.

Hughes A, Everitt B, Herbert J (1990) Comparative effects of preoptic area infusions of opioid peptides, lesions and castration on sexual behaviour in male rats: studies of instrumental behaviour, conditioned place preference and partner preference. Psychopharmacology (Berl). 102: 243–56.

Hutcheson DM, Everitt B, Robbins T, Dickinson A (2001) The role of withdrawal in heroin addiction: enhances reward or promotes avoidance? Nat Neurosci. 4(9): 943–47.

Ito R, Robbins T, Everitt B (2004) Differential control over cocaine-seeking behavior by nucleus accumbens core and shell. Nat Neurosci. 7: 389–97.

Ito R, Dalley J, Robbins T, Everitt B (2002) Dopamine release in the dorsal striatum during cocaine-seeking behavior under the control of a drug-associated cue. J Neurosci. 22: 6247–53.

Ito R, Robbins T, Pennartz C, Everitt BJ (2008) Functional interaction between the hippocampus and nucleus accumbens shell is necessary for the acquisition of appetitive spatial context conditioning. J Neurosci. 28: 6950–59.

Ito R, Dalley J, Howes SR, Robbins TW, Everitt BJ (2000) Dissociation in conditioned dopamine release in the nucleus accumbens core and shell in response to cocaine cues and during cocaine-seeking behavior in rats. J Neurosci. 20(19): 7489–95.

Johnson MH, Everitt BJ (1980) Essential Reproduction. Oxford, UK: Blackwell Scientific Publications.

Jongen-Relo A, Voorn P, Groenewegen H (1994) Immunohistochemical characterization of the shell and core territories of the nucleus accumbens in the rat. Eur J Neurosci. 6: 1255–64.

Jonkman S, Pelloux Y, Everitt BJ (2012a) Drug intake is sufficient, but conditioning is not necessary for the emergence of compulsive cocaine seeking after extended self-administration. Neuropsychopharmacology. 37: 1612–19.

Jonkman S, Pelloux Y, Everitt BJ (2012b) Differential roles of the dorsolateral and midlateral striatum in punished cocaine seeking. J Neurosci. 32: 4645–50.

Kelley AE, Domesick VB, Nauta WJ (1982) The amygdalostriatal projection in the rat--an anatomical study by anterograde and retrograde tracing methods. Neuroscience. 7: 615–30.

Killcross S, Robbins TW, Everitt BJ (1997) Different types of fear-conditioned behaviour mediated by separate nuclei within amygdala. Nature. 388: 377–80.

Lee J, Di Ciano P, Thomas K, Everitt B (2005) Disrupting reconsolidation of drug memories reduces cocaine-seeking behavior. Neuron. 47: 795–801.

Lee JL, Everitt BJ, Thomas KL (2004) Independent cellular processes for hippocampal memory consolidation and reconsolidation. Science. 304: 839–43.

Lee JL, Milton AL, Everitt BJ (2006) Reconsolidation and extinction of conditioned fear: inhibition and potentiation. J Neurosci. 26: 10051–56.

Markou A, Arroyo M, Everitt B (1999) Effect of contingent and non-contingent cocaine on drug-seeking behavior measured using a second-order schedule of cocaine reinforcement in rats. Neuropsychopharmacology. 20: 542–55.

McGaughy J, Dalley J, Morrison C, Everitt B, Robbins T (2002) Selective behavioral and neurochemical effects of cholinergic lesions produced by intrabasalis infusions of 192 IgG-saporin on attentional performance in a five-choice serial reaction time task. J Neurosci. 22: 1905–13.

Merlo E, Milton AL, Goozee ZY, Theobald DE, Everitt BJ (2014) Reconsolidation and extinction are dissociable and mutually exclusive processes: behavioral and molecular evidence. J Neurosci. 34: 2422–31.

Miles F, Everitt B, Dickinson A (2003) Oral cocaine seeking by rats: action or habit? Behav Neurosci. 117: 927–38.

Milton A, Lee JLC, Everitt BJ (2008a) Reconsolidation of appetitive memories for both natural and drug reinforcement is dependent on {beta}-adrenergic receptors. Learn Mem. 15: 88–92.

Milton A, Lee J, Butler V, Gardner R, Everitt BJ (2008b) Intra-amygdala and systemic antagonism of NMDA receptors prevents the reconsolidation of drug-associated memory and impairs subsequently both novel and previously acquired drug-seeking behaviors. J Neurosci. 28: 8230–37.

Milton AL, Merlo E, Ratano P, Gregory BL, Dumbreck JK, Everitt BJ (2013) Double dissociation of the requirement for GluN2B- and GluN2A-containing NMDA receptors in the destabilization and restabilization of a reconsolidating memory. J Neurosci. 33: 1109–15.

Misanin JR, Miller RR, Lewis DJ (1968) Retrograde amnesia produced by electroconvulsive shock after reactivation of a consolidated memory trace. Science. 160: 554–55.

Mogenson GJ, Jones DL, Yim CY (1980) From motivation to action: functional interface between the limbic system and the motor system. Prog Neurobiol. 14: 69–97.

Muir JL, Dunnett SB, Robbins TW, Everitt BJ (1992) Attentional functions of the forebrain cholinergic systems: effects of intraventricular hemicholinium, physostigmine, basal forebrain lesions and intracortical grafts on a multiple-choice serial reaction time task. Exp Brain Res. 89: 611–22.

Murray JE, Belin D, Everitt BJ (2012) Double dissociation of the dorsomedial and dorsolateral striatal control over the acquisition and performance of cocaine seeking. Neuropsychopharmacology. 37: 2456–66.

Murray JE, Belin-Rauscent A, Simon M, Giuliano C, Benoit-Marand M, Everitt BJ, Belin D (2015) Basolateral and central amygdala differentially recruit and maintain dorsolateral striatum-dependent cocaine-seeking habits. Nat Commun. 6: 10088.

Nader K, Schafe G, Le Doux J (2000) Fear memories require protein synthesis in the amygdala for reconsolidation after retrieval. Nature. 406: 722–26.

Olmstead M, Lafond M, Everitt BJ, Dickinson A (2001) Cocaine seeking by rats is a goal-directed action. Behav Neurosci. 115: 394–402.

Olmstead M, Parkinson J, Miles F, Everitt BJ, Dickinson A (2000) Cocaine-seeking by rats: regulation, reinforcement and activation. Psychopharmacology. 152: 123–31.

Page KJ, Everitt BJ (1995) The distribution of neurons coexpressing immunoreactivity to AMPA-sensitive glutamate receptor subtypes (GluR1-4) and nerve growth factor receptor in the rat basal forebrain. Eur J Neurosci. 7: 1022–33.

Page KJ, Sirinathsinghji DJ, Everitt BJ (1995) AMPA-induced lesions of the basal forebrain differentially affect cholinergic and non-cholinergic neurons: lesion assessment using quantitative in situ hybridization histochemistry. Eur J Neurosci. 7: 1012–21.

Page KJ, Everitt BJ, Robbins TW, Marston HM, Wilkinson LS (1991) Dissociable effects on spatial maze and passive avoidance acquisition and retention following AMPA- and ibotenic acid-induced excitotoxic lesions of the basal forebrain in rats: differential dependence on cholinergic neuronal loss. Neuroscience. 43: 457–72.

Parkinson J, Willoughby P, Robbins TW, Everitt BJ (2000a) Disconnection of the anterior cingulate cortex and nucleus accumbens core impairs Pavlovian approach behavior: Further evidence for limbic cortical-ventral striatopallidal systems. Behav Neurosci. 114: 42–63.

Parkinson JA, Robbins TW, Everitt BJ (2000b) Dissociable roles of the central and basolateral amygdala in appetitive emotional learning. Eur J Neurosci. 12(1): 405–13.

Parkinson JA, Olmstead MC, Burns LH, Robbins TW, Everitt BJ (1999) Dissociation in effects of lesions of the nucleus accumbens core and shell on appetitive pavlovian approach behavior and the potentiation of conditioned reinforcement and locomotor activity by D-amphetamine. J Neurosci. 19: 2401–11.

Parkinson JA, Dalley JW, Cardinal RN, Bamford A, B. F, Lachenal G, N. R, K.M. H, Robbins TW, Everitt BJ (2004) Nucleus accumbens dopamine depletion impairs both acquisition and performance of appetitive Pavlovian approach behaviour: implications for mesoaccumbens dopamine function. Behav Brain Res. 137(1–2): 149–63.

Pelloux Y, Everitt BJ, Dickinson A (2007) Compulsive drug seeking by rats under punishment: effects of drug taking history. Psychopharmacology. 194: 127–37.

Pelloux Y, Murray JE, Everitt BJ (2015) Differential vulnerability to the punishment of cocaine related behaviours: effects of locus of punishment, cocaine taking history and alternative reinforcer availability. Psychopharmacology (Berl). 232: 125–34.

Pelloux Y, Dilleen R, Economidou D, Theobald D, Everitt BJ (2012) Reduced forebrain serotonin transmission is causally involved in the development of compulsive cocaine seeking in rats. Neuropsychopharmacology. 37: 2505–14.

Pilla M, Perachon S, Sautel F, Garrido F, Mann A, Wermuth CG, Schwartz JC, Everitt BJ, Sokoloff P (1999) Selective inhibition of cocaine-seeking behaviour by a partial dopamine D-3 receptor agonist. Nature. 400: 371–75.

Robbins T, Everitt B (1982) Functional studies of the central catecholamines. Int Rev Neurobiol. 23: 303–65.

Robbins T, McAlonan G, Muir JL, Everitt B (1997) Cognitive enhancers in theory and practice: studies of the cholinergic hypothesis of cognitive deficits in Alzheimer’s disease. Behav Brain Res. 83: 15–23.

Robinson TE, Berridge KC (1993) The neural basis of drug craving: an incentive-sensitization theory of addiction. Brain Res Rev. 18: 247–91.

Robledo P, Robbins TW, Everitt BJ (1996) Effects of excitotoxic lesions of the central amygdaloid nucleus on the potentiation of reward-related stimuli by intra-accumbens amphetamine. Behav Neurosci. 110: 981–90.

Schramm MJ, Everitt BJ, Milton AL (2016) Bidirectional modulation of alcohol-associated memory reconsolidation through manipulation of adrenergic signaling. Neuropsychopharmacology. 41: 1103–11.

Selden NR, Everitt BJ, Jarrard LE, Robbins TW (1991) Complementary roles for the amygdala and hippocampus in aversive conditioning to explicit and contextual cues. Neuroscience. 42: 335–50.

Soeter M, Kindt M (2015) An abrupt transformation of phobic behavior after a post-retrieval amnesic agent. Biol Psych. 78: 880–86.

Taylor JR, Robbins T (1986) 6-Hydroxydopamine lesions of the nucleus accumbens, but not of the caudate nucleus, attenuate enhanced responding with reward-related stimuli produced by intra-accumbens d-amphetamine. Psychopharmacology (Berl). 90: 390–97.

Thomas KL, Everitt BJ (2001) Limbic-cortical-ventral striatal activation during retrieval of a discrete cocaine-associated stimulus: a cellular imaging study with gamma protein kinase C expression. J Neurosci. 21: 2526–35.

Ungerstedt U (1971) Adipsia and aphagia after 6-hydroxydopamine induced degeneration of the nigro-striatal dopamine system. Acta Physiol Scand. Suppl 367: 95–122.

Vanderschuren L, Di Ciano P, Everitt B (2005) Involvement of the dorsal striatum in cue-controlled cocaine seeking. J Neurosci. 25: 8665–70.

Volkow N, Fowler J, Wang G (2004) The addicted human brain viewed in the light of imaging studies: brain circuits and treatment strategies. Neuropharmacology. 47(Suppl 1): 3–13.

Weiskrantz L (1956) Behavioral changes associated with ablation of the amygdaloid complex in monkeys. J Comp Physiol Psychol. 49: 381–91.

Whitelaw RB, Markou A, Robbins TW, Everitt BJ (1996) Excitotoxic lesions of the basolateral amygdala impair the acquisition of cocaine-seeking behaviour under a second-order schedule of reinforcement. Psychopharmacology (Berl). 127: 213–24.

Willuhn I, Burgeno LM, Everitt BJ, Phillips PE (2012) Hierarchical recruitment of phasic dopamine signaling in the striatum during the progression of cocaine use. Proc Natl Acad Sci USA. 109: 20703–08.

Xue YX, Deng JH, Chen YY, Zhang LB, Wu P, Huang GD, Luo YX, Bao YP, Wang YM, Shaham Y, Shi J, Lu L (2017) Effect of selective inhibition of reactivated nicotine-associated memories with propranolol on nicotine craving. JAMA Psych. 74: 224–32.

Zapata A, Minney V, Shippenberg T (2010) Shift from goal-directed to habitual cocaine seeking after prolonged experience in rats. J Neurosci. 30: 15457–63.

Ziauddeen H, Nathan PJ, Dodds C, Maltby K, Miller SR, Waterworth D, Song K, Warren L, Hosking L, Zucchetto M, Bush M, Johnson LV, Sarai B, Mogg K, Bradley BP, Richards DB, Fletcher PC, Bullmore ET (2013) The effects of alcohol on the pharmacokinetics and pharmacodynamics of the selective mu-opioid receptor antagonist GSK1521498 in healthy subjects. J Clin Pharmacol. 53: 1078–90.

Tamás F. Freund

BORN:

Zirc, Hungary

June 14, 1959

EDUCATION:

Loránd Eötvös University, Budapest, Hungary, Biologist (1983)

Semmelweis University, Budapest and Hungarian Academy of Sciences, PhD (1986)

APPOINTMENTS:

Postdoctoral Fellow, Anatomy, Semmelweis University–Hungarian Academy of Sciences (1986–1990)

Visiting Research Fellow, MRC Unit, Pharmacology, Oxford University (1986–1988)

Head of Department, Institute of Experimental Medicine, Hungarian Academy of Sciences (IEM-HAS), Budapest (1990–1994)

Professor, IEM-HAS, Deputy Director (1994–2002) and Director (2002–present)

Professor and Head of Department, Péter Pázmány Catholic University, Budapest (2000–present)

HONORS AND AWARDS (SELECTED)

Drs. C. and F. Demuth Swiss Medical Research Foundation Award, Switzerland (1991)

KRIEG Cortical Kudos Cortical Explorer Award of the Cajal Club (1991, USA)

KRIEG Cortical Kudos Cortical Discoverer Award and the Cajal Medal (1998, USA)

Dargut and Milena Kemali Foundation Award, FENS Forum, Berlin (1998)

Fellow, Hungarian Academy of Sciences (1998), Vice President (since 2014)

Bolyai Prize (2000), Széchenyi Prize, (2005), Prima Primissima Award (2013, Hungary)

Fellow, Academia Europaea (2000, London) and Academia Scientiarum et Artium Europaea (2001)

Fellow, German Academy of Sciences Leopoldina (2001)

President, Federation of European Neuroscience Societies (FENS, 2004–2006)

The Brain Prize (2011, Grete Lundbeck Foundation, Denmark)

Fellow, American Academy of Arts and Sciences (2014)

Doctor Honoris Causa, University of Southern Finland (2015)

Tamás Freund’s main achievements include the discovery of new molecular pathways in nerve cell communication, identity and principles of neuron connectivity fundamental to cortical circuitry, and the generation of network activity patterns underlying multiple stages of information processing and storage in the brain. He made significant discoveries relating to structure and function of cortical microcircuits, particularly the inhibitory components and their relationship to the oscillations that underlie different stages of memory formation in the hippocampus. He discovered that GABAergic (inhibitory) pacemaker neurons in the septal region selectively innervate GABAergic interneurons in the hippocampus, thereby synchronizing activity rhythmically at theta frequency. His results in the epilepsy field provided evidence that early loss of inhibitory interneurons leads to conditions that allow interictal spiking to generate hyperexcitable circuits and ultimately lead to the chronic phase characterized by spontaneous seizures. He described the pattern of ischemic vulnerability of different cell types and regions in the brain, and its correlation with excitotoxicity. With his research group, he discovered that CB1 cannabinoid receptor activation inhibits neurotransmitter release, described the structure and operational principles of this circuit breaker in several brain regions, and identified its relationship to the pathomechanisms of anxiety and epilepsy.

Tamás F. Freund

My ancestors were German immigrants, who moved to Hungary at the end of the 18th century, and settled as farmers in villages within 10 to 20 km of Veszprém, the capital of the county. Both of my parents grew up in one of these small German-speaking villages, Bánd, within four houses of each other. It did not therefore require much effort from my father to see my mother to her home when they were dating. In the 1950s, it was no longer possible to live from farming alone, due to the agricultural policies of the Communist regime (forced establishment of cooperatives, condemnation of successful, independent farmers, and so on) and my parents moved to Veszprém as soon as they married, in 1957. I grew up in this lovely small city 10 km from Lake Balaton, the largest lake in Central Europe, having plenty of opportunities to swim and to learn sailing and waterskiing from a young age.

Duality has always been present in my life, first my parallel loves of science and music. For a long time, I was unable to decide which field I should chose as a profession and which I should keep as a hobby. Let me share with you how this dual interest developed.

My Early Scientist Self

My parents could not afford higher education. My father’s parents’ house burned down and he had to leave the high school and go to work. My mother wanted to be a school teacher, but at the age of 15, she became seriously ill for almost a year and had to abandon grammar school. Thus, my father ended up in a chemistry research institute in Veszprém as a car dispatcher, while my mother worked in the adjacent chemistry research institute as a laboratory technician. Their workplace was responsible for my initial interest in research, mainly chemistry.

In elementary school, I went for lunch every day to my “mother’s institute,” where I could watch her do chemical reactions and measurements of concentrations, pH, and such, and where I could talk to scientists. This is how I gradually fell in love with the world of research in general, exploring what was new, seeing what nobody saw before. From age 12 to 15, I worked one month every summer in these institutes as a schoolboy, serving the scientists when they came to pick up various chemicals from the storehouse. This way I quickly became acquainted with the names of many chemicals, including their formulas, and with many basic reactions. I managed to rescue some leftover chemicals, a discarded Bunsen stand and light, glass test tubes, beakers, retorts, and alembics, and I established a serious-looking chemistry lab in the woodshed of my father’s vineyard at Lake Balaton. Of course, I did all of the reactions in the manner of a schoolkid with an experimental mind. Luckily, my eyes survived all the explosions. Once we even made some use of my hobby. My father bought a derelict wine cellar adjacent to our vineyard and planned to use the stones from its construction to build our own wine cellar. The older cellar had a very sturdy vaulted ceiling, however, which we were unable to break into even with a mallet or a hack. Fortunately, I had all the ingredients to make black gunpowder, with which we exploded the ceiling and caused the cellar to collapse. We soon had all the stones we required for our new wine cellar.

My elementary school teacher found me sufficiently talented in chemistry and sent me to various competitions, which I sometimes managed to win. My father’s friend, a chemical engineer, also gave me several practical lessons in analytical chemistry. Thus, I entered grammar school at age 14 with a rather broad knowledge of chemistry and was terribly bored during chemistry classes. However, biology began to interest me even more, especially in the third year of grammar school (age 17), when we learned about the brain for at least half a year. This biology textbook was written by Jozsef Hámori, a pupil of the famous anatomist, János Szentágothai, and contained several beautiful anatomical drawings by Szentágothai as illustrations. I was fascinated by the fact that activity in complex networks of billions of nerve cells can produce behavior, control all bodily functions, store memories, generate thoughts, and give rise to various disorders when malfunctioning. I decided then, at this young age, that I wanted to spend the rest of my life doing brain research.

My Early Musician Self

When I was 7, my parents entered me into music school. They did not ask my opinion, and I just did what I was told, as playing an instrument (mostly accordion) was a long tradition in my father’s family. My parents thought I should learn the violin, but luckily for me, the music school had no more violins available, and there were no slots in the violin teacher’s schedule either. They asked the music school director what he suggested, and he picked the clarinet for me, because they had one in stock, and there were open slots in the clarinet teacher’s schedule. I started rather enthusiastically and made visible—or should that be audible—progress day by day. But after a few years of this, I lost motivation and was annoyed by my parents forcing me to practice every day while my friends were playing soccer in the courtyard.

I was just about to abandon music school at age 12, when I saw a film on television about the life of Benny Goodman. I immediately fell in love with jazz, as well as with the improvisations of Goodman. The next day, I asked my clarinet teacher whether he had any sheet music from Goodman. Luckily he did. My teacher provided me with scores from “Rachel’s Dream” and “Variations on Paganini’s Caprice 24,” both including the improvisations written down, with piano accompaniment. The jury was rather amazed when we played these tunes at music competitions as elementary school kids at age 13–14, because they thought we really were improvising. Several invitations followed; we played at school celebrations, dancing clubs, and in the Veszprém Theater at public musical events, just to name a few.

Thus, I was already rather busy with music when I entered gymnasium (grammar school) at age 14, which further enriched my musical life. The director of the music school was an excellent conductor, he established the City Choir of Veszprém and the Veszprém Symphony Orchestra, and also conducted the choir of our high school. He knew me well as a clarinetist and convinced me to join the gymnasium choir, which I reluctantly did. I was not terribly enthusiastic about choir music. However, this changed instantly when I first participated in his choir practices, as the director was an amazingly charismatic person. Choir singing became my other lifetime passion, like clarinet, and I have been unable to stop singing in choirs ever since.

The director found my voice rather mature for my years, and I could read music. He therefore invited me to sing bass in the adult City Choir—at age 15. Also in the first year of the gymnasium, I began to play the tenor sax and established a jazz quartet with three schoolmates who played the piano, bass guitar, and drums. I left Benny Goodman’s world of swing and bebop and moved toward cool and free jazz, having John Coltrane and Miles Davis as my icons. When the leader and double-bass player of a top jazz quartet in Veszprém—Endre Nyitrai—heard us play, he invited me to join his professional band. I was 16. From then on, I played in two jazz quartets, sang in two choirs, and occasionally played second clarinet in the Symphony Orchestra of Veszprém. But I did not abandon classical music. I continued to play solo clarinet and won a couple of national competitions. My teachers wondered how I managed to study and gain good marks, with all of these musical engagements. I did not even dream, at that point, that my neurobiological studies to come a couple of decades later would shed some light on how music, and indeed, the arts in general, can enhance memory formation and creative thinking.

The Choice of a Professional Career

Up until the third year of gymnasium I was unable to make up my mind whether to become a professional musician or a scientist. My interest in chemistry gradually subsided, while music occupied all my free time. However, at age 17, my passion for neuroscience became dominant, and I made a decision for a scientific career. I thought that as a scientist I could maintain my musical activities as a hobby, but it would not work the other way around. Brain research could never be done as a hobby. There were other reasons. When touring the country with the Nyitrai Jazz Quartet, we often arrived back in Veszprém well after midnight, or even at dawn, and I hardly had time to get ready for school, sometimes without any sleep at all. I also realized that I would be working in the evenings as a musician and would not be able to participate much in raising children. I grew up in a very close and loving family and wanted to give at least as much love and care to my own kids. This seemed incompatible with a career in music. The only remaining question was how to get my scientist career started (i.e., whether to attend medical school or the Biology Faculty).

My biology teacher advised that if I wanted to do research, the Biology Faculty was the better choice, because there I would learn several subjects relevant for research. The medical school did not offer these subjects. Instead, medicine would require that I study subjects that would not be as important in research. This is how I ended up in József Attila University in Szeged, at the Biology Faculty. I chose Szeged because my girlfriend at the time expected to enter medical school there, whereas I had no special connections to any university. However, after the first year of study, I had a new girlfriend—my future wife—and moved to Budapest, where she was studying in the University of Applied Arts. No such faculty existed in Szeged. I graduated from Loránd Eötvös University in Budapest in 1983 as a biologist. This move to Budapest turned out to be crucial for my research career, because I found the best mentors of all times in Budapest, Péter Somogyi and János Szentágothai. I should thank my first wife for this decision. “Cherchez la Femme”!

The Early Years in Research as an Undergraduate

In September 1979, I enrolled in the Biology Department of Loránd Eötvös University. Serious research in the field of neuroanatomy did not exist there, and I was advised to start as a student research assistant at Semmelweis Medical School, in the Anatomy Department headed by the world-famous neuroanatomist, János Szentágothai. Péter Somogyi was a young scientist in the Szentágothai research group at the time. Because Somogyi was also a biologist by basic training, he welcomed biology students to his lab particularly warmly, including me. I spent all my spare time in his lab after the compulsory university lectures or practicals, and also most of my weekends and holidays. In a few months, I had gained the technical skills that allowed me to work on my own project, investigating the morphology and connectivity of Golgi-impregnated chandelier and double bouquet cells in the cat and monkey visual cortex by correlated light and electron microscopy. This technique had been invented by Péter, and scientists visited him from all over the world to learn it. I was lucky to learn it from him first hand.

Immunocytochemistry was not available to us in 1980, and we began to use high-affinity tritiated gamma-aminobutyric acid (GABA) or nipecotic acid uptake followed by autoradiography to identify GABAergic inhibitory neurons. Identification of the transmitter, and thereby the presumed inhibitory nature of a cell type, made our morphological studies much more interesting. However, the combination of nipecotic acid uptake, autoradiography, and Golgi impregnation had its own serious limits. We turned finally to immunocytochemistry when this technique became available, and obtained our first antisera against glutamic acid decarboxylase (GAD), the synthetizing enzyme of GABA. This coincided with my very first opportunity to visit Oxford University—for two months in the summer holiday in 1981—via a collaboration between Péter Somogyi and A. David Smith at the Department of Pharmacology. It was during this visit that I managed to solve one of the major technical problems of the lab, namely, to combine immunocytochemistry with Golgi impregnation.

Immunocytochemistry was needed to visualize chemically identified neurons or pathways. In most cases (e.g., in the case of GAD), however, the antibodies available to us did not reveal the dendritic processes or axonal arbors of the immunopositive neurons, and thus the cell type could not be identified. Conversely, Golgi impregnation revealed the processes allowing the identification of cell type, but it provided no information about the transmitter identity of the visualized neurons. Thus, a combination of Golgi impregnation with immunocytochemistry was required. All earlier attempts had failed, however, because immunostaining could be done only on 60- to 80-micron-thick sections because of the limited penetration of antibodies. Golgi impregnation, by contrast, always had been done on much thicker blocks of tissue, which were sectioned only after the impregnation procedure was performed. Immunostaining could not be done after the Golgi impregnation because of the osmium treatment.

The solution to this problem came to me from the physical chemistry practicals held at the university, a subject that I disliked the most. In these classes we used U-shaped glass tubes filled with agar to connect two electrolyte solutions. I realized that if we cut 60- to 80-micron—thick sections from a tissue block and immunostained them as usual, we then could reassemble the sections into the original block of tissue using agar to hold them together. This thin layer of agar allowed the diffusion of potassium dichromate, osmium tetroxide, and silver nitrate into the tissue blocks, as needed for Golgi impregnation. The use of this technique gave rise to several important discoveries, for example, the identification of the postsynaptic elements of dopaminergic fibers in the striatum and the classification of GAD-positive interneuron types in the cerebral cortex. These studies resulted in an invitation from Professor A. David Smith to come back to Oxford for an entire year as an undergraduate in 1982–1983. The dean of Eötvös University gave me permission to spend the fifth year of my undergraduate studies in Oxford, but only if I passed all the fifth-year exams in my fourth year. So I did.

The major project of the Oxford lab led by A. David Smith at that time was the connectivity of the basal ganglia in relation to Parkinson’s disease, with a particular emphasis on how the dopaminergic neurons that are known to degenerate in Parkinson’s influence striatal neurons. The dogma at that time was that dopaminergic fibers make hardly any synapses. They simply release dopamine nonsynaptically, and the dopamine diffuses to all potential target cells that carry the appropriate receptors. Thus, it was thought, that target selectivity was determined not by synapses terminating on certain cell types, or on their specific compartments, but rather by the cellular and subcellular localization of dopamine receptors. In contrast to this view, I found that dopaminergic fibers did make synapses. This discovery was made possible by my section-Golgi impregnation technique, which allowed for the combination of Golgi impregnation, immunocytochemistry for tyrosine hydroxylase (TH), and retrograde transport of horseradish peroxidase (HRP).

The synapses of dopaminergic fibers most often were established on the necks of dendritic spines of medium spiny neurons that projected to the substantia nigra. The heads of those spines received cortical or thalamic excitatory input. Thus, the dopaminergic fibers were in an ideal position to shunt the excitatory input selectively, at the level of individual spines. This discovery was published in 1984 in the journal Neuroscience (Freund et al., 1984) and has been cited extensively each year since publication. When I was just in the middle of these studies in 1982, Francis Crick—who at that time was working on dendritic spines as potential sites of memory storage and had just proposed a model in which spines twitch in response to synaptic stimulation—visited Oxford. David Smith invited him down to the electron microscopy lab, and gave me an opportunity to show Crick my results about dopaminergic fibers selectively innervating the necks of dendritic spines. Crick really liked what he saw and was amazed by this specificity, which led him to think immediately about how to incorporate this phenomenon into his model.

Meeting the Nobel laureate, who with Watson used the data obtained from Rosalind Franklin’s unique X-ray crystallography studies to make one of the greatest discoveries in the history of biology, was a really great experience for a young Hungarian, who had just managed to move out from behind the iron curtain. Crick and Watson had seemed unreachable stars, or demigods from my school desk when I made first the decision to become a biologist. But there I was only five or six years later in Oxford, one of the capitals of world science, discussing my discovery with one of these demigods. This was like a real fairytale. Similar experiences at a young age can seriously contribute to a lifetime motivation in science. I was even younger when Sir John Eccles visited János Szentágothai in Budapest, who guided him to our lab in the basement of the Anatomy Department. That was the time when I made my first drawings of double-bouquet and chandelier cells, which he looked at with interest, and gave us encouraging comments.

Another important encounter in 1983 in Oxford was with Anders Björklund, who was on sabbatical in Cambridge, working on transplantation of embryonic dopaminergic neurons into the denervated striatum (a rat model of Parkinson’s disease). Björklund popped over to visit David’s lab in Oxford. When he saw my data on the termination pattern of dopaminergic fibers in the normal striatum, and I saw his light micrographs of dopaminergic fibers reinnervating the denervated striatum, we raised the obvious question of whether the transplanted embryonic dopaminergic neurons would find the same targets in the host striatum. The results surprised us all. I had already shown that in the normal striatum dopaminergic fibers form synapses mostly with spines and dendritic shafts of medium spiny projection neurons (Freund et al., 1984), but no morphological signs of any interactions with other axon terminals had been observed. We therefore assumed that the pharmacologically demonstrated dopaminergic control of acetylcholine release in striatal slices can be brought about only by dopaminergic receptors located on cholinergic axon terminals, where the receptors bind nonsynaptically released dopamine.

All cholinergic axons in the striatum originate from the giant cholinergic interneurons. Although these account for only about 2 percent of all striatal neurons, they give rise to an extremely dense fiber meshwork. Dopaminergic axons form a similarly dense network. Thus, the conditions are ideal for a presynaptic nonsynaptic interaction between the two transmitter systems. What I found instead in the denervated striatum that had been reinnervated by embryonic dopaminergic neurons was really astonishing. Most of the synaptic contacts on the necks of dendritic spines were reestablished, but in addition, the cell bodies of the giant cholinergic interneurons had been selectively hyperinnervated by dopaminergic fibers! They formed dense basket-like arrays of axon collaterals, some of which even got folded into the cytoplasm of the giant cells. Nothing like that has ever been seen in the normal striatum. Our hypothetical interpretation was that the dopaminergic fiber meshwork originating from the transplanted embryonic nigra was too sparse for an efficient nonsynaptic–presynaptic control of cholinergic transmission. However, the dopaminergic fibers had been able to regain normal control over acetylcholine release by hyperinnervating the parent cell bodies of the vast cholinergic fiber networks (Freund et al., 1985a). This discovery led to the continuation of this exciting collaboration, also involving my good friend and colleague in Oxford, Paul Bolam, and a visit to Lund in 1985.

Motivation and commitment to research is also enhanced by having the opportunity to publish the results in leading journals. I was very lucky from that respect as well, since Péter Somogyi’s studies of GABAergic neurons and their roles in the columnar organization of cortex had reached the most exciting stage exactly at the time when I joined his lab. This led to my easily earned, and perhaps not really deserved co-authorship on a Nature (Somogyi et al., 1981) and a Proceedings of the National Academy of Sciences (Somogyi et al., 1983) paper as an undergraduate. During my undergraduate years, I also made sufficient contributions to be the first author in a Neuroscience and a Journal of Comparative Neurology paper, both of which came out in 1983 (Freund & Somogyi, 1983; Freund et al., 1983).

Back in Budapest in 1983, I defended my diploma work at Loránd Eötvös University and received my university doctorate one year later. I carried on with my studies in the Anatomy Department under the official supervision of János Szentágothai, since Péter Somogyi was already working as a visiting professor in Australia. The head of the department in the early eighties was also the head of the university’s Communist party section. She was afraid that over the weekends or in the late evenings, we were going to use the photocopying machine of the electron microscopy lab to copy various political samizdat literature and confiscated our keys to the lab. However, Péter and I borrowed the keys from the cleaning lady, took them to the workshop of the department, and chiseled copies for ourselves. This illustrates our determination and motivation at that time, and also the presence of a Communist dictatorship, although Hungary was regarded by the west as “the happiest barrack.”

Thanks to János Szentágothai’s good political connections, Hungarian scientists had a chance to travel to the west for conferences, or even for longer visits coupled to collaborations. Szentágothai has never been associated with the Communist party, but since he was a member of not only western Academies of Sciences, but also of the Soviet Academy, the Communist leadership was unable to push him aside, or prevent him becoming the president of the Hungarian Academy of Sciences. Szentágothai had to provide a written personal guarantee that I would come back from Oxford from my 1982–1983 trip. This was the condition under which the government would allow my wife to come with me. Just a funny illustration of the regime’s operations: My first student, Iván Soltesz—now the holder of an endowed chair in Stanford—went to work with Péter Somogyi in Oxford for she Summer holidays in 1984 by train. He took several microscope slides, tissue blocks, and camera lucida drawings of neurons with him to continue analyzing them with Péter. When the train arrived at the Austrian border, Hungarian border guards began checking passports, visas, and luggage. They searched Ivan’s plastic cylinder containing the drawings, and when Ivan said these were drawings of nerve cells, they snapped at him pointing to the cell body: “come on . . . , don’t be joking! Where is this meeting point? Who is going to meet there? And where are these roads to the meeting point coming from”—they asked pointing to the dendrites. We can hardly stop laughing at this now, but at that time, it was rather scary. Ivan was taken off the train by border police, and into custody, until I was able to reach Szentágothai by phone. He managed to get Ivan out and back on the next train.

In 1985, I went to Oxford again, this time to learn electrophysiology in the lab of Kevan Martin and David Whitteridge in the Experimental Psychology Department. I never learned enough to carry out electrophysiological experiments myself, especially not in vivo. Nevertheless, I learned what is possible with these techniques, as well as how to provide a functional interpretation of our anatomical findings. I also learned to always ask functional questions regardless of whether anatomical, electrophysiological, or pharmacological approaches are used. This visit also gave rise to a number of valuable discoveries in the visual cortex and the thalamocortical system in cats, combining in vivo electrophysiology with intracellular HRP filling and target analyses using immunocytochemistry at the electron microscopic level (Freund et al., 1985b, 1989b).

Switching to the Hippocampus and the Septohippocampal System

During my visit to Anders Björklund’s lab in Lund in 1985, I also met Fred (Rusty) Gage. Interestingly, it was this cooperation with Anders and Rusty that led to my lifelong friendship and collaboration with Gyuri Buzsáki, who also was involved in joint studies with Anders and Rusty at that time. Gyuri has always been an extremely charismatic, enthusiastic, and motivating person. Thus, it is not surprising that even a couple of conversations with him gave rise to my interest in the hippocampus and the septohippocampal system that remained in the focus of my research for the rest of my career. It all started with Anders sending to Budapest about 20 rats that had gone through transplantation of embryonic dopaminergic neurons into the denervated striatum, and one to two months of behavioral testing to demonstrate functional recovery of the nigrostriatal system. Rusty arrived on the same flight with the animals to assist in the anatomical experiments, and we went together to the air cargo depot in the airport to pick them up. However, all 20 rats arrived dead, since—as we learned later—they were left outside overnight in winter when transferred between planes in Copenhagen airport. We were obviously terribly disappointed, but wanted to make a good use of the free time and decided to visit Gyuri Buzsáki in Pécs until Rusty’s return flight a couple of days later. On the train toward Pécs, Rusty told me about the discrepancies in the literature concerning the role of septal cholinergic neurons in driving hippocampal theta activity. The slow metabotropic cholinergic actions seemed most unlikely to drive any rhythmic activity, but he mentioned a group of noncholinergic—presumably GABAergic—neurons in the medial septum that might be suited for a pacemaker job. At that time, nobody knew anything about the termination pattern or postsynaptic targets of this cell group in the hippocampus, nor had any direct evidence for its transmitter being produced. These questions stimulated my first experiments in the septohippocampal system, which I began to investigate when back in Oxford in 1986.

Having defended my candidate of sciences degree (equivalent these days to PhD) in the Hungarian Academy of Sciences, I went back to Oxford in 1986, this time for two and a half years. I was working in the MRC Anatomical Neuropharmacology Unit that had been established around that time under the co-directorship of A. David Smith and Péter Somogyi. My salary came from FIDIA, an Italian pharmaceutical company, to investigate the protective effects of gangliosides in ischemia. However, the ischemia models had to be established first, obviously in the hippocampus, not only because it was my newly found favorite region, but also because it was one of the most vulnerable areas in ischemia. Thus, instead of testing gangliosides, I investigated the basic mechanisms of delayed neuronal death and selective vulnerability of specific cell types in the hippocampus in various models of global forebrain ischemia (Freund et al., 1989a, 1990a; Schmidt-Kastner & Freund, 1991; Freund et al., 1992).

These studies, together with the newly formed friendship with Gyuri Buzsáki, led to my ultimate switch to the hippocampus and related structures. I had a lucky start in this field, given that the study that I had already planned on the train traveling with Rusty to Gyuri Buzsáki in Pécs produced really exciting results. I managed to demonstrate that GABAergic septohippocampal neurons selectively innervate GABAergic interneurons in the hippocampus, which seemed to be an ideal circuit to produce rhythmic population synchrony, and it gave an answer to the age-old question of how septal pacemaker units can induce theta activity in the hippocampus (Freund & Antal, 1988). This conclusion was confirmed later in vivo by Gyuri Buzsáki and in vitro in a joint study with Richard Miles in Paris, using the septohippocampal slice preparation I developed in his lab together with my former doctoral student, Katalin Tóth (Tóth et al., 1997). This discovery of the innervation pattern of GABAergic septohippocampal neurons stimulated numerous studies that revealed, for example, the neurochemical identity and connectivity of the target interneurons, and the existence of the septocortical pathway with the same target selectivity in the phylogenetically most ancient cortex—the dorsolateral cortex of the lizard (Martínez-Guijarro & Freund, 1992)—as well as in the monkey (Gulyás et al., 1991). We also described the existence of the GABAergic basal forebrain-neocortical projection in rat, cat, and money and demonstrated that these projections were also selective in innervating interneurons only (Freund & Gulyás, 1991; Freund & Meskenaite, 1992).

Most of this work was carried out in Budapest, where I returned in 1989 upon invitation of E. Sylvester Vizi, director of the Institute of Experimental Medicine (IEM) of the Hungarian Academy of Sciences (HAS). He offered me a head of department position in his institute, which was an offer difficult to refuse, since earlier department heads in this institute were usually senior academicians. Thus, for a scientist of 30 years of age, this was a really great opportunity. I believe that for a young scientist the most important issue, even more important than salary, is being able to test as many of his or her hypotheses as possible, which requires many hands and brains. At the IEM, I had the opportunity to build up a rather large lab in a short time, taking all my students and young postdocs with me from the Anatomy Department of Semmelweis Medical School. The Morphology Department at the IEM changed its focus under my leadership and was renamed the Department of Functional Neuroanatomy. The entire institute was slowly converted into a multidisciplinary brain research center under E. Sylvester Vizi’s directorship.

From the mid-1980s, major changes happened also in my private life. With my first wife, who is a talented painter artist, we had our first child, Éva, in 1985. Éva inherited her mother’s artistic vein and graduated from the University of Fine Arts in Budapest, as a sculptor. She tried to find some links to her father’s profession as well and obtained another diploma as art therapist, working with psychiatrists on the differential diagnosis and treatment of schizophrenic patients. She made excellent portrait sculptures of Santiago Ramon y Cajal and János Szentágothai, which stand in the Szentágothai square just in front of the main building of Semmelweis Medical School, facing each other as if they were debating serious anatomical questions. A copy of both sculptures also can be found in the entrance hall of our institute. Our son Adam, who was born in 1991, also tried to find a career as far as possible from his father’s, and graduated at the University of Theatre and Film Arts in Budapest. He became a successful film director. Adam’s diploma film, Earthly People, was among the 2017 Student Academy Awards Finalists in Los Angeles. The film is about a crazy scientist father, who works day and night in the barn of their countryside house, trying to make a spaceship from washing machine spare parts and similar bits and pieces. Only his son believed in him. The wife and daughter just scoffed at him until he successfully launched himself into outer space. The film is about how different family members relate to this unexpected event later on. One may wonder where Adam got the mad scientist idea from.

During the 1990s, our circuit and molecular-level anatomy, immunocytochemistry, tracing studies, and light and electron microscopy gave rise to numerous discoveries, mostly in the hippocampus and related structures. However, it was clear from the very beginning that the functional implications of these studies would remain speculative, unless we were to provide direct electrophysiological or pharmacological confirmation. Initially, we handled this shortcoming through collaborations with physiology labs—that is, with Gyuri Buzsáki’s in vivo lab during the mid-1980s, and later on with the in vitro labs of István Módy at the University of California, Los Angeles (UCLA) and Richard Miles of the Pasteur Institute in Paris. In addition to collaborating with us, each of these three colleagues and close friends took on the responsibility of training young scientists from my lab, so that high-standard electrophysiology could be started in Budapest as well. Most of my students and postdocs—including, for example, Katalin Tóth, Iván Soltész, Attila Gulyás, László Acsády, Norbert Hájos, Attila Sík, and Viktor Varga—had a chance to study for a couple of years in one of these labs, and more than half of them returned to Budapest, which is not a bad rate. In addition to training, we had joint grants with these three labs, which allowed us to build several well-equipped electrophysiology workstations in IEM and to become a truly multidisciplinary department. Young Hungarian talents, like Gábor Nyiri, in addition to some of those just mentioned, were fortunate to have the opportunity to work in Péter Somogyi’s lab in Oxford, while István Katona received excellent training in molecular biology while working in Hannah Monyer’s and Peter Seeburg’s lab in Heidelberg.

With such a research group, having Attila Gulyás as my deputy group leader, we were able to tackle complex questions, such as the electrophysiological characterization of individual, morphologically identified inhibitory and excitatory synapses using intracellular recording and filling of connected cell pairs in hippocampal slices (Gulyás et al., 1993a, 1993b; Miles et al., 1996). We also performed analysis and functional characterization of the hippocampo-septal and the septohippocampal projections, identification of new interneuron types, and localization of transmitter receptors with a molecular level resolution. Perhaps the most interesting finding in the interneuron classification field was the discovery of interneurons that selectively innervated other interneurons in the hippocampus, forming the basis of local circuit disinhibition. Such interneurons had not been mentioned in the literature earlier, not even at the conceptual level. Using immunostaining for vasoactive intestinal polypeptide (VIP) and calretinin (CR), we described three types of interneuron-selective interneurons (Acsády et al., 1996; Gulyás et al., 1996; Hájos et al., 1996). The most interesting type was a bipolar or bitufted cell in stratum radiatum, which sent its axon to the border of stratum oriens and alveus, where it selectively innervated the cell bodies and dendrites of somatostatin-containing GABAergic interneurons: the dendrites visualized using mGluR1a immunostaining. The CR-containing cells could be found in all layers and innervated a less-well-defined, and perhaps heterogenous, group of interneurons in stratum radiatum and oriens. Local disinhibitory interneurons subsequently have been described also in the neocortex.

An interesting finding in 1990 was that the serotonergic projection from the median raphe targeted a select population of interneurons in the hippocampus, a projection similar to the septohippocampal GABAergic projection (Freund et al., 1990b). This suggested that numerically sparse subcortical projections, which carry information about motivation, emotions, and autonomic state, gain powerful global control over cortical activity patterns by modulating inhibition. This hypothesis gave rise to another series of studies that bear fruit even today. The in vivo electrophysiology lab in my group led by Viktor Varga provided evidence that the median raphe input to the hippocampus co-releases glutamate and serotonin, and selectively activates certain interneuron types through both glutamate (AMPA and NMDA) and serotonin (5HT3) receptors (Varga et al., 2009), and thereby controls hippocampal population discharge patterns. Predictions of our hippocampo-septal anatomical studies (Tóth et al., 1993) have been successfully tested by Varga’s group. Using optogenetics combined with juxtacellular recordings and Ca²⁺ imaging, they demonstrated that hippocampo-septal GABAergic neurons are activated rapidly during movement onset, and in turn, inhibit septal pacemaker units.

Investigations of the median raphe also continue today. The team of Gábor Nyiri in my lab discovered a group of glutamatergic neurons in the median raphe that did not contain serotonin. These neurons represent the largest known output of the median raphe and serve as a key hub for the acquisition of negative experience. They showed that these cells receive an extensive convergence of inputs from aversion- and memory-related brain centers, and in turn, massively innervate both the lateral habenula/ventral tegmental area axis as well as the septohippocampal system. In vivo electrophysiological recordings confirmed that these neurons are activated selectively by aversive but not by rewarding stimuli. Their activation induced acute and conditioned place aversion, pathological aggression, depression-related anhedonia, and a memory acquisition-promoting change in the state of the septohippocampal system. In contrast, precise inhibition of these cells at the moment of the aversive stimulus strongly disrupted the expression of both contextual and cued fear memories and prevented fear generalization. These discoveries may have profound implications for normal and pathological processing of negative experience as well as for the development of new effective therapies for mood disorders (Szo˝nyi et al., 2019a).

The year 2019 was a really productive and serendipitous year for my lab, because the same group, led by Gábor Nyiri, managed to make another discovery that was found worthy for publication by the editors of Science (Szo˝nyi et al., 2019b). They showed that the nucleus incertus, a small cell group in the brain stem, sends a GABAergic (and relaxin3-containing) projection to the hippocampus, selectively innervating the somatostatin-containing interneurons that in turn inhibit the most distal dendrites of pyramidal cells. Thus, they control inhibition that terminates in conjunction with the entorhinal pathway and regulates its efficacy. Thus, the nucleus incertus, responding selectively to salient stimuli, reduces inhibitory control of entorhinal excitation of hippocampal pyramidal cells, thereby generating ideal conditions for memory formation—that is, they can efficiently influence the selection and sparsity of the group of memory-encoding pyramids.

The knowledge that accumulated in the 1980s and 1990s about inhibition, interneurons, and their subcortical control was assembled into a monograph by Gyuri Buzsáki and myself, titled “Interneurons of the Hippocampus” (Freund & Buzsáki, 1996), which is extensively quoted. It has received, so far, more than 2,000 citations and has been called by our colleagues worldwide the “Interneuron Bible.” Writing this review and preparing all the illustrations was a really hard but most enjoyable work, which I did together with Gyuri while I visited him at Rutgers University in Newark, New Jersey, for two months. It was published as an entire regular issue of the journal Hippocampus.

A successful new direction of research was opened in the lab in 1996, when Ken Mackie invited me to his poster at the Society for Neuroscience meeting showing his initial immunostainings with his CB1 cannabinoid receptor antibody. For the experienced anatomist eye, it was immediately apparent that a specific type of interneuron expresses the cannabinoid receptor protein at high levels in all cortical areas, most intensely in the hippocampus. We started a collaboration with Ken, and began a series of investigations on this topic, using correlated light and electron microscopy with his antibodies, in vitro electrophysiology, pharmacology, and behavior. István Katona, a very talented undergraduate student started research work in my lab around that time. He was ambitious and skillful enough to gain responsibility for the morphological aspects of the project. First, we demonstrated the selective presynaptic expression of CB1 on axon terminals of CCK-containing interneurons in the hippocampus.

Electrophysiological experiments, which paved the way to the discovery of retrograde synaptic signaling, were performed by Norbert Hájos, and pharmacology, demonstrating the CB1 receptor-mediated decrease in GABA release by Beáta Sperlágh and E. Sylvester Vizi (Katona et al., 1999; Hájos et al., 2000). In a review in Trends in Neuroscience titled “Rhythm and Mood in Perisomatic Inhibition” (Freund, 2003), I arrived at the conclusion that while parvalbumin-containing basket cells operate as a clockwork for hippocampal oscillations, CCK-containing basket cells fine-tuned the oscillations as a function of motivational and emotional state. If the clockwork malfunctions, cortical operations may collapse, but if CCK basket cells fail, the most likely outcome would be mood disorders.

The CCK basket cells seem to be the common denominators of several types of neurochemical impairments that ultimately lead to anxiety, because they are the only cell type that expresses receptors for all anxiolytics know so far. This gave me the idea that if CB1 is also expressed by CCK basket cells, they should definitely modulate anxiety, which we successfully proved in collaboration with József Haller’s group at the IEM, demonstrating that CB1 receptor knockout mice showed significantly high levels of anxiety in all models tested, whereas CB1 agonists were anxiolytic (Haller et al., 2002, 2004). Knowing that the doctor cannot prescribe marijuana for an anxious patient, at least not in Hungary at the moment, we had to find another way to exploit this discovery. We demonstrated that the endogenous cannabinoid that regulates GABA release from CCK basket terminals is 2-arachidonoylglycerol, or 2-AG, which is synthesized by diacylglycerol lipase and metabolized by monoacylglycerol lipase (Gulyás et al., 2004; Makara et al., 2005). We hypothesized that by inhibiting the metabolism of 2-AG we can achieve an enhancement of 2-AG levels, which is released specifically in space and time—that is, it continues to be synthesized only when and where it is demanded, but because it stays around longer, it may have effects similar to those of exogenous CB1 agonists, but without the well-known side-effects.

Our cannabinoid studies then changed gear, and—mostly with the direct supervision of István Katona—led to the discovery of CB1 receptors also on glutamatergic boutons, the subsynaptic localization of the synthesizing and degrading enzymes of endocannabinoids, the discovery of the perisynaptic signaling machinery with diacylglycerol lipase coupled to mGluR5 in the perisynaptic membrane to detect glutamate spillover, the retrograde endocannabinoid signaling at glutamatergic excitatory synapses that operate as a circuit breaker, and its role in the generation of epileptic activity (Katona et al., 2006). This series of studies led to the birth of two important reviews in the field, one we wrote together with István Katona and Daniele Piomelli in Physiological Reviews (Freund et al., 2003), and the other with István only in Annual Review of Neuroscience (Katona & Freund, 2012). In addition, in a paper in Nature Medicine, written with István, we postulated the existence of a perisynaptic signaling machinery that, in general, could control the release of several transmitters and could function as a circuit breaker in several neuronal or even non-neuronal systems (Katona & Freund, 2008). István then established his own lab and has since carried on with cannabinoid signaling-related work at very high standards.

During these two decades (1990s and 2000s), my administrative responsibilities also grew considerably. In 1994, Sylvester Vizi appointed me deputy director of the IEM, and when he became president of the Hungarian Academy of Sciences in 2002, I became his successor as director. In the year 2000, the Péter Pázmány Catholic University started the Faculty of Information Technology focusing on bioinformatics, infobionics, robotics, and computational neuroscience. The founding dean, Tamás Roska, and the rector, Cardinal Péter Erdo˝, invited me to chair the Department of Neuroscience, and organize a one-year curriculum for third-year students in neuroscience. In 1998, I was elected as corresponding member of the Hungarian Academy of Sciences, regular member in 2004, and vice president in 2014. I was also very lucky to gain recognition abroad, becoming a member of the Academia Europaea (London, 2000), the Academia Europaea Scientiarum and Artium (2001), the German Academy of Sciences Leopoldina (2001), and the American Academy of Arts and Sciences (2014). In 2019, I became a member of the Pontifical Academy for Life.

I also took my share of administrative responsibilities in scientific societies and organizations in Hungary as well as abroad. When IBRO reorganized its leadership, I was elected chair of the Central and Eastern European Regional Committee, and I was a member of the Executive Committee of IBRO from 1999 till 2005. I served as president of the Federation of European Neuroscience Societies (FENS) from 2004 to 2006 and of the Hungarian Neuroscience Society from 2009 to 2013. It was a great honor to become a member of President Barroso’s Science and Technology Advisory Council in the EU (2013–2014). I also served as a member of the Committee on Committees of the Society for Neuroscience of the USA (2011–2013) and served as chair of its Young Investigator Award Selection Committee.

I was fortunate to be presented with several awards both in Hungary and abroad, although I am fully aware that awards and prizes do not necessarily indicate the value of someone’s contribution to scientific knowledge. As a colleague of mine bitterly explained, “those get awards, who are given one.” Nevertheless, I would like to mention one, as it indicates the value of the long-term collaboration and friendship with my mentors. The Brain Prize was established in year 2011 by the Lundbeck Foundation in Denmark. This is a €1 million prize given to scientists who have made major contributions to any field of neuroscience. The first awardees were three Hungarian neuroscientists, Gyuri Buzsáki, Péter Somogyi, and myself. This was a great honor, indeed, particularly knowing that the prestige of a new prize is going to be set largely by those who receive it. We were proud of it also because this prize shed new light on Hungarian neuroscience, which had long traditions and had earned worldwide respect in the past. Thus, we considered it as a well-deserved award of our great ancestors: János Szentágothai, who was such an important mentor for Péter and myself, and Endre Grastyán, who was a mentor to Gyuri. The prize also indicated that long-term collaborations between research groups that have overlapping focus, but different approaches, can be very productive and successful. Péter was my first mentor in the first decade of my career, while joint studies with Gyuri began in 1985.

I believe that the greatest benefit Hungarian neuroscience has received from my activities was not my discoveries, but the lobbying for the Hungarian Brain Research Program (HBRP). When I served as president of FENS, I was automatically a member of the board of the European Brain Council (EBC), a lobby alliance that united all European organizations with an interest in neuroscience (i.e., besides FENS, the European societies of neurologists, psychiatrists, neurosurgeons, neuropharmacologists, patient organizations, alliances of drug companies, and medical device companies). One of the major achievements of EBC was that brain research became a priority in two successive EU funding cycles (Framework Programs 6 and 7). This probably also had an influence on the establishment of the Human Brain Project, the largest research funding by the EU in history. This success was brought about largely by the “Cost of Disorders of the Brain in Europe” study initiated by the EBC, which came up with scary figures that estimated the annual costs to be about €800 billion, which is larger than cardiovascular, cancer, diabetes, and rheumatoid arthritis combined, and still increasing. Using these figures, as well as EBC’s lobbying strategy and power, I was able to convince the Hungarian government about the importance of brain research for society, for the healthcare system, and for the economy. I also argued that—in contrast to Hungarian soccer—Hungarian neuroscience not only has great traditions but also remains successful even today (e.g., see winners of the first Brain Prize, and the high number of European Research Council grants won by Hungarian neuroscientists). Thus, numerous arguments suggest that it is worth investing in brain research in Hungary, developing further the successful laboratories, and even establishing new ones. In the first four-year period (2013–2017), the Hungarian Brain Research Program received €40 million in support from the government, and in the second (2018-2022), it received an additional €22 million, which were the largest grants ever given in Hungary in any field of research. About 120 labs have been supported by this funding. More than 30 labs were newly established, several of which are headed by scientists who have returned from abroad as a result of our invitation and the available HBRP funding.

Throughout my scientific career, I’ve put considerable emphasis on disseminating research achievements to the general public, trying to translate our results to lay language, and making stories relevant and enjoyable to everyone, often by somewhat overinterpreting the data. A favorite topic of mine when delivering such lectures, a topic that also bridged the gap between my neuroscience and music interest, was “brain waves, memory and creativity, the effects of our inner world and information explosion.” Our studies on the subcortical control of the hippocampus showed how selective innervation of interneurons by the pathways carrying information about motivation and emotions (i.e., our inner world) explains the great efficiency of these pathways in driving hippocampal oscillations and synchrony, which thereby can control the efficacy of storage and recall of memory traces. A slightly far-fetched conclusion from this discovery is that it also explains the well-known experience of everyone that we perfectly remember events, regardless of how long ago they happened, if they have intense emotional attributes. From this respect, it doesn’t matter whether it was a tragic or a joyful experience. Motivation appears to operate in the same way.

If all of this is true, then the most important tasks from the point of efficient storage, recall, and creativity are (1) to let our brain circuits have a chance to incorporate our inner world influences efficiently into processes of memory formation, and (2) to enrich this inner world by artistic impressions, cathartic experiences, positive thinking, a desire to better understand the material world, and our mental environment (i.e., observing moral and ethical values). Inappropriate handling of information explosion, bolting down nonselected information (e.g., surfing on the internet while gradually loosing initial motivation and emotional attitude) will result in the superficial storage of information from which no creative new ideas will emerge. Such memory traces lack a handle by which we could drag them out from unconscious storage sites during a creative thinking process. According to recent evidence, it is recall rather than storage that represents the bottleneck in making memories useful. In contrast, the involvement of our inner world in the processes of memory formation would not help much, if this inner world is poor and disbelieving. This has led to the conclusion that the inner world—particularly our range of emotions—has to be enriched and be maintained in such a state. Perhaps the easiest and most enjoyable way to achieve this is through artistic experiences, or even more efficiently by actively participating in artistic activities, in the creation of artistic values that could include playing in chamber orchestras, singing in choirs, participating in drama study groups, dancing, folk-art ensembles, and film clubs.

Music Accompanied My Entire Life

When someone regularly practices music in professional choirs or ensembles, or plays an instrument in a jazz band, it is hardly possible to abandon it even for a short period. Thus, wherever life took me, I searched for a possibility to sing or play the clarinet or sax, and if there were no such choirs or bands, we established one. For example, I had to go to the army for 11 months for a basic training at age 18, before starting university. This was the regular practice in Hungary in those years. We established a gospel quartet in our army base, singing Negro spirituals at quite high standards, even winning nationwide competitions that resulted in weeks of extra leave of absence. Thus, even this otherwise-wasted year, could not pass without musical activity. During the first year at the university in Szeged, our gospel quartet joined the Szeged University Choir, but in addition, we formed a chamber choir as well by inviting the best sopranos and altos from the main choir. This gave rise to the establishment of the Canticum Singers, which won the major nationwide cultural competition in Hungary as well as international festivals. At the Anatomy Department of Semmelweis Medical School, where I began my scientific work in 1980, we established a choir called the Budapest Anatomists Choir, which had the nickname “Body-washer’s Singers,” because, when there were no free rooms for choir practice in the department, we had to use the autopsy room.

Currently, I am singing in Ars Nova Sacra, which is a semiprofessional chamber choir consisting of professional musicians who graduated in the Music Academy of Budapest as instrumental soloists or conductors, as well as medical doctors, lawyers, and teachers. We have recorded three CDs, and we regularly perform in Hungary as well as occasionally abroad. My clarinet and saxophone skills slowly declined, since to keep that in shape, you must practice almost daily, for which I obviously had no time with all my professional and family obligations. Nevertheless, I had the opportunity to play occasionally with some of the greatest professional jazz musicians of Hungary, most often with George Vukán, a pianist genius and composer, who died in 2013. Two of his film scores have been nominated for Oscar, and he accompanied international jazz icons like Philly Joe Jones, Clark Terry, and Kenny Wheeler. Our joint performances usually began with my lecture on the neuronal mechanisms of learning, memory, and creativity, as well as the involvement of our inner world enriched by arts in these processes. He then would demonstrate the amazing creativity of the human brain by improvising on three or four notes given by the audience. We concluded the evening by playing together his compositions for clarinet and piano. Even today, I occasionally play in clubs or concerts as a guest with world-famous musicians like the Hot Jazz Band.¹ My motivation to practice on the clarinet was considerably increased recently by my fiancée, who is a superb semiprofessional soprano soloist and also is working as an otorhinolaryngologist and phoniatrist physician. We tremendously enjoy playing in a trio with János Balázs, a celebrated classical pianist in Europe, although it is not easy to find music for soprano voice, clarinet, and piano. We have performed in prestigious places, like the Music Academy of Budapest, and have broadcasted live on the major classical music radio channel of Hungary² https://www.youtube.com/watch?v=OK9ExM-E9pM and in various cultural centers.

I am convinced that if I ever had any creative and original thoughts in my research career, it was largely due to an intervention of my inner world enriched by music. Whether the mechanism of this involves the entrainment of synchrony through cortical oscillations that depend on subcortical pathways that carry information about motivation and emotions, I am not sure. Nevertheless, I believe every word of the famous Hungarian composer, Zoltán Kodály, who said, “The mission of music is a better understanding, revival and expansion of our inner world. And where we reach the barriers of knowledge, music goes beyond these limits, into another world, which cannot be known, only guessed or presumed.”

Our mission, as scientists, is to use the most developed, state-of-the-art technologies of our age to push the barriers of knowledge as far out as possible. But unless we can look behind these barriers, we’ll never find the next best hypothesis, or the most suitable approach to explore the unknown. Throughout my scientific career, music was the major guide of my instincts that allowed me to flash a glance behind the limits of knowledge and occasionally to come up with hypotheses that turned out to be realistic and useful.

Selected Bibliography

Acsády, L., Arabadzisz, D., & Freund, T.F. (1996) Correlated morphological and neurochemical features identify different subsets of vasoactive intestinal polypeptide-immunoreactive interneurons in rat hippocampus. Neuroscience, 73, 299–315.

Freund, T.F., Bolam, J.P., Björklund, A., Stenevi, U., Dunnett, S.B., Powell, J.F., & Smith, A.D. (1985a) Efferent synaptic connections of grafted dopaminergic neurons reinnervating the host neostriatum: a tyrosine hydroxylase immunocytochemical study. J. Neurosci., 5, 603–616.

Freund, T.F. (2003) Interneuron Diversity series: Rhythm and mood in perisomatic inhibition. Trends Neurosci., 26, 489–495.

Freund, T.F. & Antal, M. (1988) GABA-containing neurons in the septum control inhibitory interneurons in the hippocampus. Nature, 336, 170–173.

Freund, T.F. & Buzsáki, G. (1996) Interneurons of the Hippocampus. Hippocampus, 6, 347–470.

Freund, T.F., Buzsáki, G., Leon, A., Baimbridge, K.G., & Somogyi, P. (1990a) Relationship of neuronal vulnerability and calcium binding protein immunoreactivity in ischemia. Exp. Brain Res., 83, 55–66.

Freund, T.F., Buzsáki, G., Prohaska, O.J., Leon, A., & Somogyi, P. (1989a) Simultaneous recording of local electrical activity, partial oxygen tension and temperature in the rat hippocampus with a chamber-type microelectrode. Effects of anaesthesia, ischemia and epilepsy. Neuroscience, 28, 539–549.

Freund, T.F. & Gulyás, A.I. (1991) GABAergic interneurons containing calbindin D28K or somatostatin are major targets of GABAergic basal forebrain afferents in the rat neocortex. J. Comp. Neurol., 314, 187–199.

Freund, T.F., Gulyás, A.I., Acsády, L., Görcs, T., Tóth, K., Gulyás, A.I., Acsady, L., Gorcs, T., & Toth, K. (1990b) Serotonergic control of the hippocampus via local inhibitory interneurons. Proc. Natl. Acad. Sci., 87, 8501–8505.

Freund, T.F., Katona, I., & Piomelli, D. (2003) Role of endogenous cannabinoids in synaptic signaling. Physiol. Rev., 83, 1017–1066.

Freund, T.F., Martin, K.A., Soltesz, I., Somogyi, P., & Whitteridge, D. (1989b) Arborisation pattern and postsynaptic targets of physiologically identified thalamocortical afferents in striate cortex of the macaque monkey. J. Comp. Neurol., 289, 315–336.

Freund, T.F., Martin, K.A.C., Smith, A.D., & Somogyi, P. (1983) Glutamate decarboxylase-immunoreactive terminals of Golgi-impregnated axoaxonic cells and of presumed basket cells in synaptic contact with pyramidal neurons of the cat’s visual cortex. J. Comp. Neurol., 221, 263–278.

Freund, T.F., Martin, K.A.C., Somogyi, P., & Whitteridge, D. (1985b) Innervation of cat visual areas 17 and 18 by physiologically identified X- and Y- type thalamic afferents. II. Identification of postsynaptic targets by GABA immunocytochemistry and Golgi impregnation. J. Comp. Neurol., 242, 275–291.

Freund, T.F. & Meskenaite, V. (1992) γ-Aminobutyric acid-containing basal forebrain neurons innervate inhibitory interneurons in the neocortex. Proc. Natl. Acad. Sci. U.S.A., 89, 738–742.

Freund, T.F., Powell, J.F., & Smith, A.D. (1984) Tyrosine hydroxylase-immunoreactive boutons in synaptic contact with identified striatonigral neurons, with particular reference to dendritic spines. Neuroscience, 13, 1189–1215.

Freund, T.F. & Somogyi, P. (1983) The section-Golgi impregnation procedure. 1. Description of the method and its combination with histochemistry after intracellular iontophoresis or retrograde transport of horseradish peroxidase. Neuroscience, 9, 463–474.

Freund, T.F., Ylinen, A., Miettinen, R., Pitkänen, A., Lahtinen, H., Baimbridge, K.G., & Riekkinen, P.J. (1992) Pattern of neuronal death in the rat hippocampus after status epilepticus. Relationship to calcium binding protein content and ischemic vulnerability. Brain Res. Bull., 28, 27–38.

Gulyás, A.I., Cravatt, B.F., Bracey, M.H., Dinh, T.P., Piomelli, D., Boscia, F., & Freund, T.F. (2004) Segregation of two endocannabinoid-hydrolyzing enzymes into pre- and postsynaptic compartments in the rat hippocampus, cerebellum and amygdala. Eur. J. Neurosci., 20, 441–458.

Gulyás, A.I., Hájos, N., & Freund, T.F. (1996) Interneurons containing calretinin are specialized to control other interneurons in the rat hippocampus. J. Neurosci., 16, 3397–3411.

Gulyás, A.I., Miles, R., Hájos, N., & Freund, T.F. (1993a) Precision and Variability in Postsynaptic Target Selection of Inhibitory Cells in the Hippocampal CA3 Region. Eur. J. Neurosci., 5, 1729–1751.

Gulyás, A.I., Miles, R., Sik, A., Tóth, K., Tamamaki, N., & Freund, T.F. (1993b) Hippocampal pyramidal cells excite inhibitory neurons through a single release site. Nature, 366, 683–687.

Gulyás, A.I., Seress, L., Tóth, K., Acsády, L., Antal, M., & Freund, T.F. (1991) Septal GABAergic neurons innervate inhibitory interneurons in the hippocampus of the macaque monkey. Neuroscience, 41, 381–390.

Hájos, N., Acsády, L., & Freund, T.F. (1996) Target selectivity and neurochemical characteristics of VIP-immunoreactive interneurons in the rat dentate gyrus. Eur. J. Neurosci., 8, 1415–1431.

Hájos, N., Katona, I., Naiem, S.S., MacKie, K., Ledent, C., Mody, I., & Freund, T.F. (2000) Cannabinoids inhibit hippocampal GABAergic transmission and network oscillations. Eur. J. Neurosci., 12, 3239–3249.

Haller, J., Bakos, N., Szirmay, M., Ledent, C., & Freund, T.F. (2002) The effects of genetic and pharmacological blockade of the CB1 cannabinoid receptor on anxiety. Eur. J. Neurosci., 16, 1395–1398.

Haller, J., Varga, B., Ledent, C., & Freund, T.F. (2004) CB1 cannabinoid receptors mediate anxiolytic effects: Convergent genetic and pharmacological evidence with CB1-specific agents. Behav. Pharmacol., 15, 299–304.

Katona, I. & Freund, T.F. (2008) Endocannabinoid signaling as a synaptic circuit breaker in neurological disease. Nat. Med., 14, 923–930.

Katona, I. & Freund, T.F. (2012) Multiple Functions of Endocannabinoid Signaling in the Brain. Annu. Rev. Neurosci., 35, 529–558.

Katona, I., Sperlágh, B., Sík, A., Kőfalvi, A., Vizi, E.S., Mackie, K., & Freund, T.F. (1999) Presynaptically located CB1 cannabinoid receptors regulate GABA release from axon terminals of specific hippocampal interneurons. J. Neurosci., 19, 4544–4558.

Katona, I., Urbán, G.M., Wallace, M., Ledent, C., Jung, K.M., Piomelli, D., Mackie, K., & Freund, T.F. (2006) Molecular composition of the endocannabinoid system at glutamatergic synapses. J. Neurosci., 26, 5628–5637.

Makara, J.K., Mor, M., Fegley, D., Szabó, S.I., Kathuria, S., Astarita, G., Duranti, A., Tontini, A., Tarzia, G., Rivara, S., Freund, T.F., & Piomelli, D. (2005) Selective inhibition of 2-AG hydrolysis enhances endocannabinoid signaling in hippocampus. Nat. Neurosci., 8, 1139–1141.

Martínez-Guijarro, F.J. & Freund, T.F. (1992) GABA-immunoreactive basal forebrain afferents innervate GABA-immunoreactive non-pyramidal cells in the cerebral cortex of the lizard podarcis hispanica. Neuroscience, 51, 425–437.

Miles, R., Tóth, K., Gulyás, A.I., Hájos, N., & Freund, T.F. (1996) Differences between somatic and dendritic inhibition in the hippocampus. Neuron, 16, 815–823.

Schmidt-Kastner, R. & Freund, T.F. (1991) Selective vulnerability of the hippocampus in brain ischemia. Neuroscience, 40, 599–636.

Somogyi, P., Cowey, A., Halász, N., & Freund, T.F. (1981) Vertical organization of neurones accumulating 3H-GABA in visual cortex of rhesus monkey. Nature, 294, 761–763.

Somogyi, P., Cowey, A., Kisvarday, Z.F., Freund, T.F., & Szentágothai, J. (1983) Retrograde transport of γ-amino[3H]butyric acid reveals specific interlaminar connections in the striate cortex of monkey. Proc. Natl. Acad. Sci. U. S. A., 80, 2385–2389.

Szo˝nyi, A., Sos, K.E., Nyilas, R., Schlingloff, D., Domonkos, A., Takács, V.T., Pósfai, B., Hegedüs, P., Priestley, J.B., Gundlach, A.L., Gulyás, A.I., Varga, V., Losonczy, A., Freund, T.F., & Nyiri, G. (2019b) Brainstem nucleus incertus controls contextual memory formation. Science, 364. eaaw0445.

Szo˝nyi, A., Zichó, K., Barth, A.M., Gönczi, R.T., Schlingloff, D., Török, B., Sipos, E., Major, A., Bardóczi, Z., Sos, K.E., Gulyás, A.I., Varga, V., Zelena, D., Freund, T.F., & Nyiri, G. (2019a) Median raphe controls acquisition of negative experience in the mouse. Science, 366, eaay8746.

Tóth, K., Borhegyi, Z., & Freund, T.F. (1993) Postsynaptic targets of GABAergic hippocampal neurons in the medial septum-diagonal band of broca complex. J. Neurosci., 13, 3712–3724.

Tóth, K., Freund, T.F., & Miles, R. (1997) Disinhibition of rat hippocampal pyramidal cells by GABAergic afferents from the septum. J. Physiol., 500, 463–474.

Varga, V., Losonczy, A., Zemelman, B. V., Borhegyi, Z., Nyiri, G., Domonkos, A., Hangya, B., Holderith, N., Magee, J.C., & Freund, T.F. (2009) Fast synaptic subcortical control of hippocampal circuits. Science, 326, 449–453.

¹“A Hot Jazz Band vendége Freund Tamás, klarinét,” Alexander’s Ragtime Band, MOMKult, December 30, 2018, video, 4:24, https://www.youtube.com/watch?v=jni5sGPTe14, https://www.youtube.com/watch?v=UpqGgHQbDr8.

²“Schubert: Der Hirt auf dem Felsen, D.965,” Bihari, Freund, Balázs, video, 11:49, https://www.youtube.com/watch?v=OK9ExM-E9pM.

Uta Frith

BORN:

Rockenhausen, Germany

May 25, 1941

EDUCATION:

Universität des Saarlandes, Saarbrücken, Vordiplom in Psychology (1964)

University of London, Diploma in Abnormal Psychology (1966)

University of London, PhD (1969)

APPOINTMENTS:

Medical Research Council Scientific Staff (1969–2006)

Professor of Cognitive Development University College London (1996–present)

Visiting Professor University of Aarhus, Denmark (2006–2015)

HONORS AND AWARDS (SELECTED)

President British Science Association (2017)

Jean Nicod Prize CNRS ENS, jointly with Chris Frith (2014)

William James Fellow Lifetime Achievement Award, APA (2013)

Foreign Associate National Academy of Sciences US (NAS) (2012)

DBE (Honorary Dame Commander of the British Empire) (2012)

European Latsis Prize “Brain and Mind” jointly with Chris Frith (2009)

Member Leopoldina National Academy of Germany (2009)

Lifetime Achievement Award International Association for Autism Research (2007)

Samuel T. Orton Award International Dyslexia Association (2007)

Fellow Royal Society (2005)

Fellow Academy of Medical Sciences (2001)

Fellow British Academy (2001)

Honorary Doctorates from Universities of Lincoln, Bath, Cambridge, Nottingham, Aston, York, St. Andrews, Palermo, Göteborg (1998–2018)

Uta Frith began her science career studying experimental psychology in Germany. She continued her training in clinical psychology at London University. Her doctoral thesis on pattern detection in typically developing and autistic children started her lifelong fascination with the study of neurocognitive mechanisms, which can fail, and if so, result in developmental disorders, such as autism or dyslexia. Uta Frith and her collaborators developed and tested innovative theories to explain the characteristic behavioral features of both these conditions, such as “mentalizing problems” and “weak central coherence” to explain the social and nonsocial features of autism, and phonological processing problems in dyslexia, respectively. Mentalizing, the ability to attribute mental states to others, such as intentions and beliefs, proved to be a particularly fruitful notion, and her group was the first to identify the circumscribed brain network that underpins this ability. Uta Frith is currently writing a book with Chris Frith on “What makes us social” and a graphic novel on the same topic. She is concerned about the future of science and is advocating for Slow Science. Her aim is to promote a research culture that values quality more than quantity, with the motto “less but better.” She is passionate about the role of women in science and science communication and has presented a number of BBC Horizon documentaries.

Uta Frith

I accepted the invitation to narrate my life for this volume with apprehension, knowing that I would be in the company of celebrated psychologists and neuroscientists. This is the company of dreams. But I have qualms that are hard to shake off. Who am I? My story is a story that I believe to be true, and that I would like the reader to believe in, too. Still, I am bound to be biased by a natural wish to present myself in a good light. As a scientist, I am skeptical of autobiographical accounts. Nevertheless, I have found them invaluable in helping me understand the mental world of autistic individuals. With this preamble off my chest, it turns out that I have always wanted to tell this story about my life, my favorite ideas, and my favorite people.

A Kind of Fairy Tale

Nothing predestined me to become a scientist, and the environment of my childhood was as far removed as possible from where I am today. I can’t help thinking that the unpromising beginning, the unexpected turns, and the happy ending are marks of a fairy tale.

I was born in Germany in the middle of World War II, in Rockenhausen, a very small town in the Donnersberg region of Rhineland-Palatinate. I had an idyllic childhood. It seems a miracle that it was possible for me to live untouched by the dreadful events happening at the time. My mother managed to keep me and my younger sister safe, and I well remember her singing a popular song with the refrain “Keine Angst, keine Angst, Rosmarie.” I grew up in my grandparents’ house, playing all day in the street or garden, and roaming the surrounding fields with the children from the neighborhood. My mother ran her father’s shop, known in the region as Zigarren-Gödel. From a young age, I fetched bread from the bakery that also belonged to the Gödel family.

When I was four years old, I was surprised that a strange man, my father, suddenly arrived and stayed. I learned much later that his experiences of the war had been horrific and deeply traumatizing. Wilhelm Aurnhammer was an artist and art teacher. As part of a group of expressionist artists in Munich, he was forbidden to exhibit. He trained as a teacher and was lucky to get a job in a village school in the back of beyond, not far from Rockenhausen, where he met my mother. His father had been an accountant with the BASF chemical industries in Ludwigshafen am Rhein. My Aurnhammer ancestors came from Augsburg in Southern Germany. My two grandmothers were quite different from each other, one associated with town, the other with the country.

Rockenhausen Streetview, etching by Wilhelm Aurnhammer, 1947.

The little town where I grew up was embedded in a soft landscape with meadows, hills, woods, orchards, and vineyards. I was proud to know that Hildegard von Bingen, the 12th-century polymath, was a child of the region. On each hill, there would likely be the ruin of a medieval castle. For each castle, there was a story, and the ones I remember had a heroine who withstood a siege and saved everyone by a clever ruse. Who told the stories? Mainly my mother. She also had a special love of poems, which I picked up without effort. I fondly remember an old relative, known as fairy-tale aunt, who lived on a remote farm. She had a knack for entrancing us children with her wonderfully elaborated versions of Grimm’s fairy tales.

I started primary school in 1947, but it might as well have been 1847. Horse and cart, endlessly reworked clothes, and oil lamps were part of daily life. There were old books and old toys, and not enough paper for drawing and scribbling. We learned to write using a slate, with a sponge attached to wipe it clean. My father produced a children’s book, making wood cuts for the illustrations, which accompanied verses by my uncle, and were colored thanks to the help of a local printer. A funny incident occurred on my first day at school, for which I have no memory, but a family friend, the mother of another child, told me about many years later. All the mothers were present, except mine. She had sent me along on my own, in line with her principles of instilling independence. At the time, I was unaware that this was a bit unusual. A school inspector welcomed the new intake and asked the rhetorical question: “Which of you children is the cleverest?” Apparently, I stepped forward without hesitation. Everyone laughed, but this startling self-confidence was a gift that never left me, even though it went underground on many occasions. Maybe it was a self-fulfilling prophecy, enhanced by my mother’s claim that, as I was born on a Sunday, I was bound to be lucky. It so happened that throughout my school years, I got top marks.

When I was eight years old, we moved to the nearest big town, Kaiserslautern. My father taught art at several of the secondary schools, as there was a shortage of teachers. There was also a shortage of school buildings and of everything else. Children and teachers brought logs of wood to heat schoolrooms on the coldest days. Bombing raids had destroyed much of the town, as was the case with any other town I visited. I later realized that my concept of town was of a gigantic building site of rubble and ruins. As a teacher, my father obtained a coveted apartment, when most apartments in the area were shared by several families. Large numbers of refugees had to be accommodated. We children benefited directly from the Marshall Plan as hot meals were given out at schools. I remember everyone being inventive with scarce resources. This was the best of times, as many said afterward. The terrible war was over, and the 12-year reign of terror of the Third Reich had ended, although there would be lasting wounds and lasting guilt. Remarkably, within a few years, the economic miracle converted West Germany into a modern democratic society.

The ruins disappeared gradually under rebuilt houses, but in the meantime, they furnished a tempting playground. Despite barbed wire and broken glass, every unsafe step was a thrill. There were other exciting places I was eager to explore. The woods were only minutes away from where we lived, woods that quickly turned into deep dark forest. Unsupervised, my sister and I went there carrying little baskets to bring back blueberries. We climbed up steep paths through mossy valleys and over pink sandstone rocks. I still hanker after these woods. I had started a nature diary, where I entered “observations,” with little drawings, each ending with the question, “Why was it interesting?” Was I aware that only some things drew my attention and other things didn’t? Perhaps it was the start of a phase in my own cognitive development in which I realized that it was thrilling to observe nature, and even more thrilling to observe the observer.

I fondly imagine that I reached peak energy when I was between 10 and 12 years old. Learning and memory came easily to me, and I could count on friends to play with and go on adventures. In my limited environment, I felt I could take on anything. I did not mind that other people called me ambitious, because I wanted to excel, and I craved approval. Soon enough, I found my limits and discarded various interests, such as sports, drawing, and chess, all very much to my father’s regret. Instead, I preferred reading and looking at art, listening to music, and joining in the conversation with eccentric artists and colorful relatives, when they visited the family. I was becoming “encultured” in a bourgeois-cum-bohemian home.

My parents allowed me immense freedom. They agreed readily to my wish to change from the modern secondary school where all my friends were, to the “Altsprachliches Gymnasium.” My choice was unusual because this particular school had a long tradition of preparing boys for university and was attended by only a handful of girls. I was befriended by one of the older girls, who went on to read classics at Heidelberg. One day she invited me to get a taste of what it was like to be a student. I loved everything about it. But something took me aback. She told me that she considered doing a doctorate, like her older sister before her. However, her admired professor advised her against it, as ‘she wasn’t the type’, which, he stressed, she should take as a compliment. Suprisingly, she was flattered by this response. She became a classics teacher, a job thought to be highly suitable for a clever girl, and as it turned out, she was very good at it. But somehow, I knew that Heidelberg had to go from my list of desirable universities, and classics from my list of desirable subjects.

Little did I know that my willful change of schools was tantamount to challenging well-established gender roles. Gradually, I realized I had traded in traditional femininity to become an intellectual bluestocking. What on earth made me do this? Well, I did enjoy showing off with recondite knowledge and getting better grades than the boys. I also liked the fact that the curriculum was so wide that I did not have to make any decision on whether I would take up arts or sciences at university. I was curious about everything and soaked up an indiscriminate mixture of information, especially when it went against expectations and overturned previously unquestioned beliefs. Disenchantment was enlightenment. It felt far more exciting than the enchantment of earlier times. Fairy tales were lies! There was an exhilarating frisson in the possibility that everything might be questionable. This was getting nearer to a scientific mind-set, but I still had no idea of what I was going to do when I grew up.

Into the Big Wide World

What could be more splendid than being hostess of a salon in 19th-century Paris? Drifting among intellectuals and artists for perpetual entertainment was my idea of winning life’s lottery. It was a fabulous aim to strive for, if somewhat unrealistic, but being a student at the Sorbonne seemed the next best thing. My parents accepted this plan with their customary laissez-faire. But first, I reckoned, a university near home, yet close to France, the University of the Saarland at Saarbrücken, would be a more practical idea. I knew lots of people who studied there. It was a modern university with a distinct French presence. I was 20 when I left school, but I was still a provincial girl, far more backward and naïve than young people today would be able to imagine.

What was it like to be a student with no fixed aims? I sampled lectures and seminars in a whole range of subjects. I was thrilled to get to know professors who had written books that you could find in a bookshop. I was dreaming of being an eternal student, sampling all of the disciplines on offer. Still, I focused on history of art, which quickly became my favorite subject. And no wonder. Those students were interesting, and moreover they went on trips to see art and architecture at first hand. There were trips to Paris and visits to the churches of Lorraine and of Champagne. I recommend study tours! They are far more instructive than lectures, especially about the people who study with you, not to mention the senior academics. Professor Schmoll genannt Eisenwerth lectured on captivating topics, such as the idea of the torso in Rodin’s work, the history of photography, or exquisite 14th-century sculpture. I tried to impress him with seminar presentations and preparing slides for his lectures.

Gradually, my attention was drawn to students who were following a structured career, doing exams and doctoral dissertations. Slowly, I realized that they were the ones to emulate. It was a random piece of luck that this got me into psychology. Out of curiosity, I attended a lecture, given by an earnest professor, about factor analysis and intelligence. Despite the dry delivery my interest was captured. I felt there were serious questions, and serious methods to answer them. What actually was intelligence? Did it change during development? Why were there individual differences? I eagerly offered to take part in psychometric tests, which reminded me of party games. It was fun going to the Psychology Department: it was attractively furnished, and there were original works of art on the walls. The people were cool, too. Furthermore, there was a proper course structure, very unlike what I had seen in the other subjects I had sampled.

The course involved learning about anatomy and physiology as well as statistics, which to me only made it more attractive. Ernst Boesch, a Piaget pupil, was head of department and gave lectures on development and cultural anthropology; these subjects were totally new to me and utterly absorbing. Paul Baltes was already an established student and teaching assistant and encouraged me to continue in psychology. He later became well known for his studies in life-span psychology. The course work was all novel, and some of it slightly horrifying, like the lab class that involved killing frogs to record spinal nerve activity using smoked drums. But none was as fascinating as the grand ward rounds in psychiatry. They were given by an inspiring professor, who presented patients suffering from schizophrenia, depression, phobia, obsessive-compulsive disorder (OCD), and other disorders. I could not wait for these presentations, which were by far the most mindboggling thing that I had ever come across. I desperately wanted to know what caused these disorders of the mind and, all of a sudden, I knew that I had to become a researcher in clinical psychology.

There was one big hurdle. To follow the course in experimental psychology I had to use a textbook, a standard American textbook, in English! I decided to go on an immersive language course for students in London. It was tough. But London enchanted me. Much to my own surprise, I liked it even better than Paris, and I began to wonder whether I should go to London University instead of the Sorbonne. I had read Uses and Abuses of Psychology (Eysenck, 1953) and Sense and Nonsense in Psychology (1958)—but in translation. These books had been quite a shock to me, because at that time, few people had dared to criticize psychoanalysis, and Eysenck’s books promised a better way to treat patients by applying the principles of learning theory. I was thrilled to learn that Behavior Therapy was being practiced and taught at London’s Maudsley Hospital. Clearly, this was the place for me! I applied for an internship during the summer vacation and was lucky to be taken on. I was able to help on a project on OCD led by Reg Beech, working out correlations on a massive calculator. I learned about the diploma course in abnormal psychology, which provided a wonderful and unique opportunity to train alongside clinicians and researchers. I so wished I could get on that course. As my time ended and my suitcase was already half packed, I found out that somebody had dropped out, and a place had become vacant. I will always be grateful to Monte Shapiro, who was head of the course, for his faith in me and taking me on as a trainee.

Happy Ending

This stroke of luck was nothing compared with the miraculous good fortune that led me to my future husband, Chris Frith. He was a trainee in the year before and had just started on a doctorate. It did not take us long to know that we were made for each other, a couple of days at most. The similarity of our interests, tastes, likes, and dislikes astonished us. But, perhaps these wonderfully coinciding interests were actually created and shaped by our interactions. For example, we both developed an interest in British constructionist art and enjoyed meeting the artists, to whom we were introduced by our art historian friends. One of the earliest works we acquired, a white circular relief by Susan Derges, can be seen in the background of our double portrait, which is shown at the end.

In this painting, you also can glimpse some of the influences that made me “me,” but that had nothing to do with science. They have everything to do with the beautiful things in life. I have an irrepressible desire to collect things that touch me as especially pleasing, from Persian rugs to Chinese porcelain, from Old Master prints to anonymous alphabet samplers. They fill our large Victorian home. Everything is intermingled, perhaps reflecting my omnivorous mind. As I am writing this piece, I am listening to classical music on BBC Radio 3, something I cannot do without. My favorite composers are as predictable as my favorite colors. I enjoyed talking about them on the BBC’s legendary Desert Island Disks program.

I adapted to English culture fast, but I had a lot to learn, and not just the language. I was delighted to be welcomed into the Frith family, as Chris was welcomed into the Aurnhammer family. We were married in 1966 and remain harmoniously united to this day.

Uta and Chris Frith, 1966.

We had two sons: Martin, born in 1975, and Alex, born in 1978. Neither of them took up psychology—in case you are curious, Martin is a computational biologist living in Tokyo, and Alex is a children’s book editor living in London. With three wonderful grandchildren, I cannot imagine a happier ending.

For my story to end happily, some crucial foundations had to be laid, and it was Chris who laid them. He taught me about information processing and about neuropsychology and he tutored me in statistics. He continuously kept me up to date with all the exciting developments in methods, from the very first crude computers to the very first positron emission tomography (PET) scanners. His career in research was independent of my own. We specialized deliberately, thereby enlarging our research activities, rather than doubling up skills. We were lucky enough to pursue research in distinct areas, and we avoided working in the same department. This provided enough room for dissent, as well as common ground for productive argument and discussion. We were always curious about each other’s work and talked about it constantly. We read each other’s drafts with a critical eye. I believe the continuous exchange of new information and willingness to give and take criticism was by far the most important factor in our apparently successful scientific career. At first, we only occasionally wrote a paper together, and it was not until later years that this became our favorite mode. Looking back, I feel we could feature in an advertisement for scientific collaboration. It is perhaps no coincidence that we recently have been writing mainly about social communication, cooperation, and the role of diversity in making joint decisions.

After my last Medical Research Council (MRC) program grant finished, having reached the then-normal retirement age of 65, I was touched that my colleagues and students put together a Festschrift with a meeting and subsequent volume of the papers presented (Bishop & Snowling, 2008). But now a new exciting phase of life started. Both Chris and I had been offered visiting professorships at the University of Aarhus, which we held until recently. We regularly drove to Harwich and crossed the usually stormy North Sea by ferry. For our extended stays in Denmark, we loved living in the Scandinavian style. Being able to take walks in stupendous beech woods on the Baltic provided a refreshing contrast to our London life. The Interacting Minds Centre (IMC) with Andreas Roepstorff at the helm, still serves as a multidisciplinary hub with many offshoots. Now that our positions have officially ended, we continue to visit Aarhus every year.

Breakfast of the Interacting Minds Group at the Yellow Villa at Aarhus University, ca. 2007. From left to right: Ethan Weed, Peter Vust, Giacomo Rizzolatti (invited seminar speaker), Chris Frith, Uta Frith, Kristian Tylen. Andreas Roepstorff is outside the picture.

I will now leave behind the true tale of the country mouse who ventured into a foreign land, grew fat and famous, and was even invited to one of the Queen’s garden parties. I next try to give a condensed account of the main preoccupations that dominated my work—dyslexia and autism. I will mention only some of the people who have influenced me, because if I mentioned all of them, this section would turn into a long, long list. There is more information about my life, interests, and passions on the frithmind.org website.

Obsessed with Literacy

The paradox that there are individuals who are excellent readers but atrocious spellers, excited me because it was something very dear to me: Chris was one of these individuals. I was amazed by the speed of his reading. He solved fiendishly difficult crosswords, yet he often asked me how to spell a word when entering it into the grid. How could it be that my own still quite shallow command of English included orthographic knowledge, without even trying? I made it my project to find out.

It was not long before I found similar people, whom I termed type B spellers, and I developed tests to find out whether memory representations for written words were used differently for reading and for writing. I was following the notion that we read by eye but write by ear, and there was no single lexicon in the brain that efficiently bridged both channels (Frith, 1979). The reading lexicon could be built with incomplete spelling patterns, allowing very fast recognition, but the writing lexicon needed the complete word forms, given that writing is a slow sequential process. Other researchers were interested in similar questions, and I thought it would be fun to edit a book on spelling that brought this new work together (Frith, 1980). And it was fun. First, because I was in close contact with the process of production with the long-defunct publisher, Academic Press. Apparently, it was one of the last books to be typeset and printed by an artisan printer. Second, it was great to meet up with the authors to talk about their chapters, accompanied by strawberries and fizz in the summer and gingerbread and mulled wine in the winter. Oh for the good old days, when we were happy with such simple pleasures.

Although there were plenty of books on teaching reading, there was not a lot of theory about the development of reading and spelling. I thought of it as a stepwise process, with the use of three different strategies (Frith, 1986). First, I proposed, reading would be accomplished by holistic (logographic) impressions; second, this strategy would be opposed by another (alphabetic) one, which would automatically arise from learning to write, a sequential process; third, both strategies would be integrated in a mature (orthographic) strategy of the skilled normal reader. The type B spellers would manage to get to only the second step. The dyslexics (i.e., those who were poor readers as well as poor spellers) presumably would not manage step two. This may all sound simpleminded, but it served as a framework to carry out experiments that addressed the question of how children acquire literacy, and sometimes fail to do so.

Letter reversals that are typical of beginners, were of particular fascination to me (Frith, 1974), and I first thought of reading as part of visual perceptual development. However, I completely changed my mind about this. And this dates from a summer school run by the Society for Research Child Development at the University of Delaware in 1974. I applied and was amazed and delighted to be accepted. The experience was truly “formative”: my first time in the United States, first time being among like-minded young researchers, and first time meeting famous psychologists. Lila Gleitman left an indelible impression, and it was her presentations that convinced me that learning to read and write had far more to do with language development than with visual perception. However, the most lasting influence on me were my fellow students, with Linnea Ehri, George Marsh, Rod Barron, Rob Kail, and Lynn Waterhouse among them.

Listening to Isabelle Liberman and Don Shankweiler I remember the frisson of insight, when I realized that the way I thought about spoken language had been indelibly “corrupted” by my own literacy. Words and the sounds of letters are rather unnatural segments to cut out from the natural flow of speech, and yet we feel them as natural segments. I took this as a striking lesson in how culture shapes our thought processes.

In the 1960s and 1970s, many people claimed that dyslexia had no biological basis and that a medical model for the condition only played into the hands of middle-class parents trying to explain away their children’s poor school achievements. I was not convinced. The children’s difficulties were “specific,” that is, their other cognitive abilities were seemingly intact. The contrast would be general intellectual impairment, where difficulty in learning to read (as difficulties in other areas) was only to be expected. Furthermore, there were strong indications that dyslexia ran in families and a genetic predisposition seemed likely. I had an inkling that some unknown and possibly subtle brain abnormality, dating from before birth, could have long-lasting but circumscribed effects. This was somewhat at odds with the prevailing assumption that the heightened plasticity of young brains would readily enable reorganization and compensation. It was very much at odds with the then-popular assumption that psychosocial factors caused disorders, such as dyslexia and autism.

My interest in dyslexia was fired up by the arrival of my first doctoral student, Maggie Snowling, in the 1970s. Maggie’s research was foundational in putting grapheme-phoneme skills at the center of investigations and putting the focus on phonological deficits. Later, we set up a study with children at genetic/family risk for dyslexia. We found telltale signs of phonological problems even at the preschool age (Gallagher, Snowling & Frith, 2000). Franck Ramus, of the next generation of dyslexia researchers, joined me as a postdoc in 2000. He systematically compared the three then prevailing theories of dyslexia (Ramus et al., 2003). It was a tense contest, but the phonological deficit theory won. Sadly, we still don’t know precisely what phonological deficit, at a cognitive and neural level, actually means. More work is needed.

I believe that my forays into literacy development and disorder were hugely propelled by the possibility of brain imaging. This was an exciting moment in my personal history, and a turning point in my growing collaborations with Chris. Could we see what was wrong in the brain of dyslexics? This was at the time when PET scanning had just become available. Unfortunately, it was suitable only for adults given the potential risks of this method. This meant finding adult dyslexics when previously I had studied only children. The same applied to autism. It was clear to me that dyslexia and autism did not disappear in adulthood, even if behavioral symptoms improved markedly. Dyslexics, in particular, tended to achieve “average” scores on standard reading and spelling tests. For a behaviorist it was unthinkable that they could still be dyslexic. Poor reading and spelling were the very definition of dyslexia, and this was the model I resolved to overturn.

The argument was won with the demonstration that dyslexia manifests differently in behavioral tests in different languages but bears the same brain signature (Paulesu et al., 2001). Italian, for example, is a language with a transparent orthography, so that almost anyone with knowledge of the grapheme-phoneme rules, can pass a reading test, even dyslexics. Guided by the phonological deficit theory, my colleagues and I developed tests that tap into phoneme manipulation (think “pig Latin”) and naming speed (e.g., colors or numbers) and thus could act as behavioral markers of dyslexia, in Italian as well as in French and English. The cross-language work in Italy was led by Eraldo Paulesu and, in France, by Jean-François Démonet, with a grant from the European Union. As a result of this project, we were able to show that culture-specific writing systems not only shape the way we read, but also shape the relevant regions of the brain (Paulesu et al., 2000).

My interest in reading, spelling, and dyslexia ran along a parallel track to my interest in autism (Frith, 2013). I justified these parallel research streams with the firm belief that I might be able to understand cognitive development better if I understood what could go wrong in development, and that I might be able to do this by comparing the apparent fragility of different cognitive abilities, both resulting in lifelong, if sometimes subtle, impairments. But how did this way of thinking start? How did I get there?

One inspiration was the ground-breaking work by Elizabeth Warrington and Tim Shallice with neuropsychological patients. For example, they studied in depth two patients recovering from encephalitis and found significant discrepancies in their ability to identify or define different categories of objects (Warrington & Shallice, 1984). Remarkably, they were much better at identifying inanimate than animate stimuli, whether from pictures or words. They were also better at defining abstract words (e.g., caution) compared with concrete words (e.g., cabbage). I was struck that it was possible to find such dissociations and eager to learn if it was possible to find them also in children with developmental disorders. My ambition was nothing less than to “cut nature at the joints” (Frith, 2012) to identify “modules of the mind.”

But it was not just the fantastic idea of circumscribed mental modules that might be glimpsed when they have faults. I also believed that such modules could relate to very abstract capacities. I was never drawn to investigate low-level acoustic processes in dyslexia, and likewise, low-level sensory processes in autism. Perhaps under the nostalgic influence of Gestalt psychology, I was not convinced by a simple forward processing model, and in order to explore cognitive impairments I did not feel I had to start at the bottom level of the processing hierarchy. Instead, I was excited by the idea that primary problems might originate at quite high levels with top-down effects on lower-level perception.

It might have seemed obvious, but it took my brilliant young colleague, Sarah-Jayne Blakemore, to make me think about implications of my work for education. Our book (Blakemore & Frith, 2005) was the result of an intensely enjoyable collaboration.

Incurably Drawn to Autism

I now rewind back to 1965–1966 when any of this was still far from my mind. I was training in clinical psychology and eager to do research. I had already earmarked OCD as a possible topic for a doctorate. But the unexpected happened. As part of the rotation to different departments, I found myself on the Children’s Ward. Michael Rutter led a ward round discussion of an autistic child whose parents had come to consult him from as far away as South Africa. I was immediately struck by the little five-year-old boy. He had a bright expression, but did not talk, and I was deeply puzzled about what tests to use to find out what he was or was not able to do. I found an article about perceptual abilities of autistic children by Beate Hermelin and Neil O’Connor (1964) and was astonished to learn that the authors were right there at the Maudsley Hospital. Someone pointed them out to me in the lunch queue of the canteen. They stood out by their almost exotic chic. With great trepidation I approached them, and to my amazement, they invited me not just once but twice to discuss some of their work. I reveled in the privilege. I learned that they had already started on a whole series of psychological experiments on autism that they were to summarize in a monograph (Hermelin & O’Connor, 1970).

This encounter changed everything. The glamorous duo, Beate Hermelin and Neil O’Connor, were to be my most important role models. I compared them to the Avengers, heroes of a then-popular television series (Frith, 2009). I have to talk about them together because they carried out all their research in collaboration and alternated authorship of their papers.

I was overjoyed when Beate, known as Ati, offered to take me on as a doctoral student. She later told me that she had made the decision on the grounds that I had been very critical of one of her experiments. She was unconventional in many ways and never went along with received opinion. I, on the other hand, was shocked that I could have been so forward when I had been overawed by her. The most thrilling part of our discussion was not about autism at all, but about the possibility of a back door into understanding intelligence, precisely by studying individuals who were of very limited intelligence. For example, by comparing children who either did or did not speak, it might be possible to find out something about the role of language in learning and memory.

Beate Hermelin and Neil O’Connor, ca. 1980.

I started as an apprentice, observing Neil and Ati, while doing a replication and follow-up of an experiment that contrasted recall of random and meaningful sequences (O’Connor & Hermelin, 1967). The astonishing finding was that there was no advantage in meaningful sequences for autistic children. They could repeat back as many of the random as of the meaningfully arranged words. If their memory did not take advantage of meaning, did they not get the meaning?

My doctoral thesis was meant to be about problems of motor coordination in autistic children, but I felt so passionately about the recall paradigm and the promise to find out something about the secret of “meaning” in the brain, that I begged to be allowed to continue along these lines. I embarked on a series of experiments that used binary patterns as stimuli, words and colors. This work gave rise to the rather vague notion of a drive for meaning or “central coherence,” which I proposed was weak in autism. I did not know about Bayes at the time, but if I had, I would have used the term “weak priors.”

I did not get any further however, until Amitta Shah, one of my early doctoral students, came up with the idea of testing autistic children’s ability to find hidden figures (Shah & Frith, 1983). Much to our amazement, they were very good at it, far better than the comparison group of nonautistic intellectually impaired children. This allowed us to put the spotlight on cognitive strengths in autistic children. Their excellent attention to detail might explain why they paid more attention to an earring than to the person wearing it. It might also explain savant skills, such as excellent rote memory or absolute pitch. These ideas were taken up and refined by a later doctoral student, Francesca Happé (Happé & Frith, 2006). More recently, this work has been extended in terms of Bayesian models (Lawson, Mathys & Rees, 2017). Even before I finished my thesis, Neil O’Connor asked me if I would join him at his research unit, funded by the MRC, and to be located at University College London (UCL). This was my dream job, and I didn’t even have to apply for it.

Uta Frith and Neil O’Connor, ca. 1971.

Neil also hired psycholinguist Rick Cromer, fresh from his doctoral work with Roger Brown at Harvard. We bonded straight away. I was incredibly sad that Rick became an early victim of the AIDS epidemic without having had a chance to fulfill his promise. The MRC Developmental Psychology Unit, to give it its full name, was highly productive given its tiny size with two senior and two junior researchers, a research assistant, a technician, and a secretary (Bryant, 1983). Rick and I were given utmost freedom to do the research we wanted to do. We benefited from visitors who stayed for sabbatical periods, such as Jacques Mehler and Jerry Bruner. Rick, Neil, and Ati had a huge influence not only on my work but also on my outlook on life. The four of us went to lunch together every day, and our conversation was mostly about art, theater, and literature. There was always time to visit one of the major London museums and browse antiquarian bookshops. It now seems a golden age in which pressure to publish was felt far less than pressure to cultivate style.

Rick Cromer, ca.1985, demonstrating a psycholinguistic experiment: “The wolf is eager to bite” versus “The wolf is easy to bite. Who does the biting?” Young Sarah-Jane Leslie has to act out what the sentences mean and demonstrates who bites whom.

Theory of Mind (Mentalizing)

Neil O’Connor retired in 1982 and John Morton became director of the MRC Cognitive Development Unit. This was a much larger unit, with a distinctive ethos that emphasized theory over data collection. In intense discussions, new ideas emerged, and arguably the most startling of these was “Theory of Mind” as an explanation of the social difficulties in autism.

Mentalizing was the name we coined for the awkward “attributing mental states” and for avoiding the awkward expression “having a Theory of Mind.” How do we best characterize and explain this novel ability? Is there a brain basis for mentalizing? When does mentalizing originate in development and in evolution? Does a fault in the mentalizing system lead to autism? We tried to answer some of these questions (Frith, Morton & Leslie, 1991). Actually, they are so hard that they are still waiting for answers more than 30 years after Alan Leslie and I discussed them over endless cups of tea. Alan was the key person in proposing a putative mechanism that might underlie this ability. His innovative and ingenious idea was that the ability to process mental states presupposed the “decoupling” of representations of the world from their actual state in the physical world (Leslie, 1987): why does John take an umbrella? Because he thinks “it is raining,” not because it is actually raining.

Alan Leslie and Uta Frith, ca. 1985, in front of Wilhelm Aurnhammer abstracts.

Alan had observed his own baby daughter laughing with delight when her mother picked up a banana to use it like a telephone. He had something like a lightbulb moment. Little Sarah-Jane, who, after all, relied on getting reliable information about the world from her parents, did not learn that bananas are for speaking into, nor that telephones are for eating. Even at age 18 months, she understood make-believe actions. By inference, she was able to distinguish physical reality from what Alan called “having an attitude to reality.” (I cannot resist mentioning that she is now a prominent philosopher at Princeton).

Now, I knew of a study that found that autistic children did not show pretend play (Wing et al., 1977). Perhaps there could be a failure somewhere along the complex path of having and recognizing an attitude to reality, perhaps a decoupling failure. So far, so circular. To get further, we needed to test this hypothesis with a novel task that required mentalizing, which if the hypothesis held up, autistic children should be unable to perform. Probably, it was part of the Zeitgeist that other groups were also interested in testing the development of “Theory of Mind” in children, and its presence or absence in other animals. Premack and Woodruff (1978) had led the way with their paper “Does the Chimpanzee Have a Theory of Mind?” We wanted to ask, “Does the Autistic Child Have a Theory of Mind?” and chose it as the title of our first paper (Baron-Cohen, Leslie & Frith, 1985). We were extremely fortunate to be able to use the false belief task invented by Heinz Wimmer and Josef Perner (1984). Heinz and Josef were to become both lifelong friends and collaborators, cemented by mutual sabbatical visits and co-supervised students. Thus, I was able to work with Josef on theory of mind (Perner et al., 1989) and with Heinz on cross-language studies of literacy acquisition (e.g., Landerl, Wimmer & Frith, 1997).

Simon Baron-Cohen was the exceptional doctoral student who did the testing and later developed his own influential theory of “mindblindness” in autism (Baron-Cohen, 1995). He used the Sally-Ann task, which goes like this: Here are two dolls, Sally and Ann. Sally has a basket; Ann has a box. Sally has a marble; she puts it into her basket. Then she goes outside to play. While she is outside, Ann takes the marble out of the basket and places it in her own box. When Sally comes back, she wants to play with her marble. Where will Sally look for her marble? Typically developing five-year-olds immediately grasp the situation and can explain readily that Sally will look in her basket because she couldn’t know that Ann put the marble into her box. She wasn’t there when the marble was moved. The interpretation is that they take into account Sally’s false belief when they predict where she will look. Amazingly, even quite able autistic children did not reliably predict Sally’s behavior on the basis of her belief.

Our hypothesis that autistic children lacked the ability to predict behavior on the basis of mental states did not rely on a single experiment, but was tested with a wide variety of paradigms. For instance, we used a picture-sequencing task, contrasting events involving mental states, and events involving physical states (Baron-Cohen, Leslie & Frith, 1986). Consistent with our claim, autistic children were superior at reconstructing physical cause-and-effect sequences. A favorite task of mine brought out the dark side of mentalizing: Beate Sodian and I contrasted (physical) sabotage with (mental) deception (Sodian & Frith, 1992). Deception, but not sabotage, depends on the ability to attribute beliefs to others and to manipulate them for one’s own advantage. Autistic children turned out to be well able to put a lock on a box to prevent a thief from stealing the contents, but they were pretty much unable to keep the thief away by (falsely) stating that the box was locked.

The comparison of good understanding of physical cause and effect and, at the same time, poor understanding of mental cause and effect is an example of “cutting nature at the joints.” These are dissociations that lay bare the circumscribed nature of a cognitive problem, and that, following Shallice and Warrington, may help us begin to understand the architecture of the mind. I felt incredibly excited that a fault in a cognitive mechanism could explain a range of diverse and demonstrably impaired behaviors in autism at one fell swoop: poor joint attention, delayed language learning, and failure in conversational turn taking are all behaviors that critically depend on taking into account others’ intentions. Other explanations of these features were either too piecemeal, or too sweeping to be useful.

Francesca Happé propelled the research on mentalizing by designing “Strange Stories,” which contrast content that does and does not require mentalizing. These stories were the basis of the first functional imaging PET study of Theory of Mind (Fletcher et al., 1995) and the first imaging study with adults with Asperger syndrome—that is, autism without language or intellectual impairment (Happé et al., 1996). Subsequently, we developed short videos of animated triangles, who interacted either in a way that provoked mentalizing (e.g., tricking one another) or else were perceived as being merely goal directed (e.g., copying) or random. This idea was based on the famous Heider and Simmel animation (1944), which had demonstrated the overpowering urge of observers to attribute desires and intentions even to geometric shapes, as long as they moved interactively. Fulvia Castelli, for her doctoral project, conducted PET scan studies with adults with Asperger syndrome who watched these videos (Castelli et al., 2000, 2002). The imaging studies highlighted a distinct network of brain regions involving medial prefrontal regions as well as regions at the junction of temporal and parietal lobes. We suggested that our results with able autistic adults showed weaker connectivity between these regions. There have been a number of similar studies in other labs, but we still do not know precisely what is different in the brain activity during mentalizing in autism. Nor do we have a computational model for the cognitive mechanism. There is lots more work to do.

But oh—the problems that met my attempts to convey this exciting science story. Even now, I despair at the misunderstandings of mentalizing that stubbornly resist attempts at clarification. I need to make clear, over and over again, that failing or passing a test is not by itself informative, because there are different ways of achieving the same behavior. It is for good reason that we need to keep our focus on cognition and not on behavior. I will come back to this point.

After several years, I realized that it was not just other people who had problems understanding mentalizing, but that I myself had a problem. A very big problem. All the mentalizing tasks we produced, in principle, could be solved within the realm of conscious deliberate thought. So, they could be solved slowly by logic and not necessarily by an automatic process served by a presumably innate mentalizing module. Intellectually able autistic people would be able to “hack” the tests. Indeed, they often performed perfectly, if somewhat slowly, suggesting that they might well apply conscious problem-solving strategies. The question was whether they would be able to show implicit (i.e., automatic) tracking of mental states.

Only after infant researchers had developed ingenious tasks that relied on automatic processes, such as eye gaze, did it become possible to answer this question. We selected autistic adults whose performance on false belief type tasks was perfect. Amazingly, they did not show the systematic anticipatory looking pattern that was shown by ordinary adults (Senju et al., 2009). These are tantalizing results, and it remains to be seen how they hold up and what they tell us. I would not be surprised if only a subgroup of individuals currently diagnosed autistic displayed a profound inability to track mental states. Would this mean the death of the mentalizing hypothesis for autism? Not just yet. If mentalizing isn’t what it used to be, autism isn’t what it used to be either.

The Changing Concept of Autism

For all questions about autism Lorna Wing and Margaret Dewey, both mothers of autistic children, were my gurus. Lorna convinced me with her arguments that led to the concept of the autism spectrum. Margaret acted as a vital advisor for my book (Frith, 1989) since I wanted to share what I knew about autism with parents like her. My book turned out to be only the first of a flood of books that are now on the market. Rainman, the popular film with Dustin Hoffman’s well observed portrayal of an autistic adult, may well have been one of the drivers of the surge in autism awareness.

At around this time, people became first aware that there were not only children but also adults with autism. Adults had been ignored by clinicians as well as researchers, and there were hot arguments about whether a person who was verbally fluent and intellectually able could have a diagnosis of autism. Lorna Wing had no doubt that they could, and she encouraged me to look at Hans Asperger’s early descriptions of such cases. It was a belated but exciting discovery, which led me to edit a book (Frith, 1991). It contained my annotated translation of Asperger’s seminal paper (1944) as well as contributions from the few people I knew who had experience of such individuals, that is, Lorna Wing, Christopher Gillberg, and Francesca Happé. Digby Tantam, a young psychiatrist whose doctoral thesis I was supervising, was another contributor, interested in both autism and schizophrenia. I was also able to persuade Margaret Dewey to contribute a chapter that, through the use of vivid vignettes, laid bare the shattering social problems of even highly intelligent autistic people.

The public response to the concept of Asperger syndrome was overwhelming. Everyone seemed to know someone who was “on the spectrum.” This trend is still continuing, but I have to confess that I am not entirely sanguine about it. It is hard for me to look in the same way at the very disabled children who participated in the early experiments and the amazingly accomplished people who are today’s favorite experimental subjects. Are they even autistic? I often wonder.

Undeterred by the fact that able autistic people can pass explicit false belief tasks, I remain attached to the hypothesis that there is at least a subgroup, whose social interaction problems are due to implicit mentalizing failure, independent of intelligence. My belief is undiminished that this is the basis for a cognitive phenotype and free from the vagaries of constantly changing diagnostic criteria (Frith, 2012). But for this to be tested robustly, we need psychometrically validated tests of mentalizing. What a pity that such tests don’t exist—yet.

Cognitive Neuroscience: A Revolution and a Revelation

Historical change is neatly marked in the names of the three centers where I was fortunate enough to have worked. The information processing revolution, which changed the course of experimental psychology had deeply influenced my work at the MRC Developmental Psychology Unit. The influence of the cognitive revolution was evident in the MRC Cognitive Development Unit. Finally, I moved to the Institute of Cognitive Neuroscience, which, as the name implies, was part of the neuroimaging revolution.

Throughout my career, I was always able to carry out my own research without any interference. However, it was only between 1998 and 2006, that I had a research group of my own, with two postdocs, a research assistant, and several doctoral students.

Some members and friends of the Institute of Cognitive Neuroscience Developmental Group, ca 2000. Front row from left to right: Francesca Happé, Tim Shallice, Uta Frith, Maria Tallandini-Shallice. Back row from left to right: Eamon McCrory, Frances Abell, Lauren Stewart, Fulvia Castelli.

What was new? We strongly felt a new beginning: a systematic approach to linking brain and mind was surely facilitated by the location of the new institute. Tim Shallice, the founding director, had managed to persuade the provost of UCL to acquire the lease of a substantial building in Queen Square, opposite the National Hospital for Nervous Diseases and Institute of Neurology, and almost next door to the innovative and already world-leading Functional Imaging Laboratory (FIL), equipped with a state-of-the-art PET and magnetic resonance imaging (MRI) scanners. We shared the building with the Gatsby Centre for Computational Neuroscience, which allowed for many fruitful interactions.

The founding members of the institute included John O’Keefe, Jon Driver, Paul Burgess, and Patrick Haggard, all of whom had their own research groups. All collaborated with the members of the FIL, which included Richard Frackowiak, Chris Frith, Karl Friston, and Ray Dolan, among others. I believe that this intense collaboration resulted in an innovative strand of work with many “firsts.” It was inspired by rigorous psychological experiments, animal and human, as well as by neuropsychological case studies. It was only natural that my collaborator in all of the imaging experiments was Chris. A constantly replenished and diverse pool of talented postdocs and doctoral students, many from countries outside the United Kingdom, was an essential ingredient in our success.

Not every cognitive scientist was happy to embrace brain imaging as the method of choice to advance our understanding of cognitive processes. I, on the other hand, could not wait to try out and learn about this new method. The rewards dazzling before my eyes were nothing less than solving the paradoxes of dyslexia and of autism, and perhaps even understanding how the mind creates meaning from information. My enthusiasm was still some years away from the inevitable disenchantment, when it became clear to me that the questions I was asking were simply too difficult to expect to result in quick answers. Worse still, perhaps I didn’t have the right questions. Nevertheless, to be able to be among the pioneers of the field was a priceless experience.

John Morton, ca 1998.

John Morton was highly skeptical of what brain imaging could contribute to cognitive models and had prepared me well for disenchantment. Already when he started his unit, he managed to shake me out of my happy-go-lucky attitude to theory and experiments. For a long time, I had been content to be led by strange phenomena, such as the paradox of being a good reader but a poor speller. I claimed that theories were airy-fairy things and that all I wanted to do was to follow up the phenomena to be rewarded by glimpses of a hidden truth. Eventually, I had a revelation. I suddenly could see that trusted data can turn out to be ephemeral and unreliable, while theories, even if proved wrong, can be important and memorable. Through marathon lab meetings that John had instituted, it had become clear to me that theories and testable hypotheses would make or break the new field of cognitive developmental neuroscience. It was exciting to think that hypotheses created by different theories could be tested against each other, even if it was hard to find the right way to test them. In particular, I was taken by the strikingly simple but controversial idea of innate mechanisms that might be the causes of specific impairments in developmental disorders. It testifies to the strong influence of Chomsky’s idea of an innate capacity for language development, which I had absorbed from Rick Cromer. Of course, it is still a bold claim that needs to be questioned continuously (Frith, 2013).

Framework for explaining developmental disorders.

John Morton and I tried to find the simplest possible framework that we could use to evaluate such radical claims and speculate about causes of developmental disorders (Morton & Frith, 1995). It was true back-of-the-envelope stuff. Basically, at the top is the level of the brain. In the middle is the level of cognition. At the bottom is the level of behavior. We suspected that there were many different, presumably genetic, causes lurking at the top level and influencing brain development, but we assumed that they converged on a bottleneck, the place of cognitive mechanisms. It seemed okay to speculate about one mechanism at a time and how it affected a whole range of behaviors. In fact, if you draw this out, it makes an X-shape.

This simple framework turned out to be useful. This was mainly because drawing lines and pointing to spaces was a way of avoiding words, which are often the main cause of misunderstandings. For example, mentalizing is just a node you can point at, occupying a particular space in the model. Of course, we’d like to have a computational model eventually, but we are not anywhere near that yet. Nevertheless, the node becomes more tangible when it is assayed by tailor-made tasks at the behavioral level and physiological measures at the brain level. I feel happy and hopeful when I can fill the ovals with putative content, starting from cognition and tracing lines in both directions, linking brain and behavior

The framework made it apparent that the distinction between cognition and behavior was often deceptively difficult, because behavioral descriptions disguise themselves as explanations. For example, the explanation of poor reading test performance by poor reading ability! Poor reading can have many causes—think of poor teaching or truancy. We saw examples of circularity everywhere. The trick was to take a counterfactual stance: If a key mechanism was missing, what kind of seemingly unrelated behaviors would be affected?

Sunset

Now I am retired and I can do what I like best: read the latest research papers on cognitive development, autism, and dyslexia. I am also feeling passionate about diversity and promoting women in science. Worried by the current replication crisis, I started campaigning for Slow Science (Frith, 2019). By this I mean upholding quality over quantity and standing up against the publish-or-perish culture. In the spirit of this, I am taking time to think and write. Jointly with Chris, we have supplied the content for a graphic novel—a nonfiction book on social cognitive neuroscience. This was then scripted by our son Alex and illustrated by the artist Dan Locke. In a parallel project, we are slowly writing an academic monograph, which is meant to provide the scientific backstory.

I spend most of my time in front of my computer. I check Twitter on my favorite topics. I follow up on new research papers. I have a to-do list that always includes writing a reference, reviewing a paper, preparing a talk, writing a blurb, or arranging speakers for a conference. It is a nice life. I recommend it to those of my colleagues, who wish to never retire. The best is the luxury to critically reflect on research I did in the past, when I did not take enough time to think. The worst is failing health, the inevitable burden of aging. There remains one important goal, and that is a good death. I would be very happy if neuroscience research could be creatively extended to obtain more information on what this means.

If I were to sum up my life in a sentence: I changed country, language, and culture and found happiness in marriage and in work far beyond anything that the fairy tales of my childhood could have prepared me for.

Portrait of Chris and Uta Frith, painted by Emma Wesley, 2008 (https://emma-wesley.co.uk/section/429750-Portraits.html).

Selected Bibliography

Asperger, H. (1944). Die ‘autistischen psychopathen’ im kindesalter. Archiv für Psychiatrie und Nervenkrankheiten 117: 76–136. Translated by U. Frith. In U. Frith (Ed.) (1991), Autism and Asperger Syndrome (pp. 36–92). Cambridge: Cambridge University Press.

Baron-Cohen, S. (1995). Mindblindness: An Essay on Autism and Theory of Mind. Cambridge, MA: MIT Press.

Baron-Cohen, S., Leslie, A.M. & Frith, U. (1985). Does the autistic child have a “theory of mind”? Cognition 21: 37–46.

Baron-Cohen, S., Leslie, A.M. & Frith, U. (1986). Mechanical, behavioural and intentional understanding of picture stories in autistic children. Br. J. Dev. Psychol. 4: 113–125.

Bishop, D.V.B. &Snowling, M. (Eds.). (2008). Neurocognitive approaches to developmental disorders: a Festschrift for Uta Frith. Q. J. Exp. Psychol. 61(1): 3–181.

Blakemore, S.J. & Frith, U. (2005). The Learning Brain. Lessons for Education. Oxford: Blackwell.

Bryant, P. (1983). Editorial: The Passing of the MRC Developmental Psychology Unit. Br. J. Dev. Psychol. 1: 303–306.

Castelli, F., Happé, F., Frith, U. & Frith, C. (2000). Movement and mind: a functional imaging study of perception and interpretation of complex intentional movement patterns. NeuroImage 12: 314–325.

Castelli, F., Frith, C.D., Happé, F. & Frith, U. (2002). Autism, Asperger syndrome and brain mechanisms for the attribution of mental states to animated shapes. Brain 125: 1839–1849.

Eysenck, H.J. (1953/1958). Uses and Abuses of Psychology. Sense and Nonsense in Psychology. London: Penguin.

Fletcher, P., Happé, F., Frith, U., Baker, S., Dolan, R., Frackowiak, R. & Frith, C.D. (1995). Other minds in the brain: A functional imaging study of “theory of mind” in story comprehension. Cognition 57: 109–128.

Frith, U. (1974). A curious effect of reversed letters explained by a theory of schema. Percept. Psychophys. 16: 113–116.

Frith, U. (1979). Reading by eye and writing by ear. In R.A. Kolers, M.E. Wrolstad & H. Bouma (Eds.), Processing of Visible Language (pp. 379–390). New York: Plenum Press.

Frith, U. (1980). Cognitive Processes in Spelling. London: Academic Press.

Frith, U. (1986). A developmental framework for developmental dyslexia. Annals of Dyslexia 36: 69–81.

Frith, U. (1989/2003). Autism: Explaining the Enigma. Oxford: Blackwell.

Frith, U. (Ed.). (1991). Autism and Asperger Syndrome. Cambridge: Cambridge University Press.

Frith, U., Morton, J. & Leslie, A. M. (1991). The cognitive basis of a biological disorder: Autism. Trends Neurosci. 14(10): 433–438.

Frith, U. (2009). Looking back: The Avengers of psychology. The Psychologist 22(8): 726–727.

Frith, U. (2012). Why we need cognitive explanations of autism. Q. J. Exp. Psychol. 65(11): 2073–2092.

Frith, U. (2013a). Autism and dyslexia: A glance over 25 years of research. Perspect. Psychol. Sci. 8(6): 670–672.

Frith, U. (2013b). Are there innate mechanisms that make us social beings? In A. Battro, S. Dehaene & W. Singer (Eds.), Neurosciences and the Human Person: New Perspectives on Human Activities (pp. 215–236). Vatican City: Pontifical Academy of Sciences.

Frith, U. (2019). Fast lane to Slow Science. Trends Cog. Sci. (24)1: 1–2.

Gallagher, A., Frith, U. & Snowling, M. (2000). Precursors of literacy delay among children at genetic risk of dyslexia. J Child Psychol Psychiat, 41, 203–213.

Happé, F. & Frith, U. (2006). The weak central coherence account: detail focused cognitive style in autism spectrum disorders. J. Autism Dev. Disord. 36(1): 5–25.

Happé, F., Ehlers, S., Fletcher, P., Frith, U., Johansson, M., Gillberg, C., Dolan, R., Frackowiak, R. & Frith, C.D. (1996). “Theory of mind” in the brain. Evidence from a PET scan study of Asperger syndrome. NeuroReport 8: 197–201.

Heider, F. & Simmel, M. (1944). An experimental study of apparent behavior. Am. J. Psychol. 57: 243–249.

Hermelin, B. & O’Connor, N. (1964). Effects of sensory input and sensory dominance on severely disturbed, autistic children and on subnormal controls. Br. J. Psychol. 55(2): 201–206.

Hermelin, B. & Frith, U. (1971). Psychological studies of childhood autism. Can autistic children make sense of what they see and hear? J. Spec. Educ. 5: 107–117.

Hermelin, B. & O’Connor, N. (1970). Psychological Experiments with Autistic Children. Oxford: Pergamon.

Landerl, K., Wimmer, H. & Frith, U. (1997). The impact of orthographic consistency on dyslexia: A German-English comparison. Cognition 63: 315–334.

Leslie, A.M. (1987). Pretense and representation: The origins of “theory of mind.” Psych. Rev. 94(4): 412–426.

Morton, J., Frith, U., Johnson, M. & Karmiloff-Smith, A. (1998). Work from the MRC Cognitive Development Unit. Dev. Sci. 1(2): 213–214.

Morton, J. & Frith, U. (1995). Causal modeling: Structural approaches to developmental psychopathology. In D. Cicchetti & D. Cohen (Eds.), Developmental Psychopathology (pp. 357–390). New York: Wiley.

Palmer, C., Lawson, R.P. & Hohwy, J. (2017). Bayesian approaches to autism: towards volatility, action and behavior. Psych. Bull. 143(5): 521–542.

Paulesu, E., McCrory, E., Fazio, F., Menoncello, L., Brunswick, N., Cappa, S.F., Cotelli, M., Cossu, G., Corte, F., Lorusso, M., Pesenti, S., Gallagher, A., Perani, D., Price, C., Frith, C.D. & Frith, U. (2000). A cultural effect on brain function. Nature Neurosci. 3: 91–96.

Paulesu, E., Démonet, J., Fazio, F., McCrory, E., Chanoine, V., Brunswick, N., Cappa, S., Cossu, G., Habib, M., Frith, C. & Frith U. (2001). Dyslexia: cultural diversity and biological unity. Science 291: 2165–2167.

Perner, J., Frith, U., Leslie, A.M. & Leekam, S. (1989). Explorations of the autistic child’s theory of mind: Knowledge, belief and communication. Child Dev., 60: 689–700.

Premack, D. & Woodruff, G. (1978). Does the chimpanzee have a theory of mind? Beh. Brain Sci. 1(4): 515–526.

Ramus, F., Rosen, S, Dakin, S., Day, B.L., Castellote, J.M., White, S. & Frith, U. (2003). Theories of developmental dyslexia: insights from a multiple case study. Brain 126: 841–865.

Senju, A., Southgate, V., White, S. & Frith, U. (2009). Mindblind eyes: an absence of spontaneous theory of mind in Asperger syndrome. Science 325(5942): 883–885.

Shah, A. & Frith, U. (1983). An islet of ability in autistic children: A research note. J. Child Psychol. Psychiat. 24(4): 613–620.

Sodian, B. & Frith, U. (1992). Deception and sabotage in autistic, retarded and normal children. J. Child Psychol. Psychiat. 33: 591–605.

Warrington, E.K. & Shallice, T. (1984). Category specific semantic impairments. Brain 107(3): 829–853.

Wimmer H. & Perner, J. (1983). Beliefs about beliefs: representation and constraining function of wrong beliefs in young children’s understanding of deception. Cognition 13(1): 103–128.

Wing, L., Gould, J., Yeates, S.R. & Brierly, L. (1977). Symbolic play in severely mentally retarded and autistic children. J. Child Psychol. Psychiat. 18(2): 167–178.

Mary B. Kennedy

BORN:

Pontiac, Michigan

July 4, 1947

EDUCATION:

St. Mary’s College, Notre Dame, IN

Johns Hopkins University, Baltimore, MD

APPOINTMENTS:

Assistant Professor of Biology, California Institute of Technology (1981–1984)

Associate Professor, California Institute of Technology (1984–1987)

Associate Professor with tenure, California Institute of Technology (1987–1992)

Professor of Biology, California Institute of Technology (1992–2002)

Allen and Lenabelle Davis Professor of Biology, California Institute of Technology (2002–2020)

Director of the Moore Center for Integrative Study of Cell Regulation, California Institute of Technology (2006–2012)

HONORS AND AWARDS (SELECTED)

McKnight Neuroscience Development Award (1984)

Faculty Award for Women Scientists and Engineers, National Science Foundation (1991)

Fellow of the American Association for the Advancement of Science (1991)

Javits Neuroscience Investigator Award, National Institutes of Health (1992)

Fellow of The American Academy of Arts and Sciences (2002)

Fondation Ipsen Prize in Neuronal Plasticity (2006)

Mary Kennedy is a pioneer in the elucidation of biochemical mechanisms underlying learning and memory. She was trained in traditional biochemistry, studying lipid metabolism in bacteria. After receiving her degree, she moved into the study of biochemical regulation in the nervous system and for the past 40 years, has studied control of synaptic plasticity in the postsynaptic spines of glutamatergic synapses. She first purified and studied calcium/calmodulin-dependent protein kinase II (CaMKII), showing that it is highly concentrated in the brain, particularly in the postsynaptic density, and becomes calcium-independent upon autophosphorylation, resulting in switch-like enzymatic behavior. She showed that CaMKII is a major target of calcium ion entering through N-methyl-D-aspartate (NMDA)-type glutamate receptors during induction of long-term potentiation. She expanded her study of the postsynaptic density by using microchemical tools and genetic engineering to discover new protein constituents, including PSD-95, the major scaffold protein of the postsynaptic density. She discovered PDZ domains within PSD-95 and, with Peter Seeburg, was the first to show the importance of PDZ domains for protein localization, including anchoring of NMDA receptors at the postsynaptic site. She has studied the roles of CaMKII and other synaptic proteins in the regulation of the number of AMPA-type glutamate receptors located at the synapse during activity-induced changes in synaptic strength.

Mary B. Kennedy

Like the Tale of Two Cities, my early life in science is two parallel stories. One is about the best that a scientific career has to offer. The other is a sad tale of the misogynistic barriers faced by women scientists of my generation. In my case, the latter tale is particularly grotesque; however, my story is not complete without it. I chose to use this autobiographical chapter to reveal how I got from Pontiac, Michigan, to Caltech, and to recount my experiences in the first six years there. Much of this material was difficult to write and may be difficult to read. But it is a story that should be told.

I have been blessed with many wonderful students and postdocs, most of whom don’t appear in these pages. I hope they know that I appreciate their friendship, support, and hard work in the lab. I also fervently hope that I did more to help them along the way than some of my early mentors did for me. I also won’t do justice to the many scientific friends and colleagues with whom I have shared meetings, dinners, and long satisfying talks. These are the people who kept me going. They include Eric Schwartz, Marge Livingstone, Kristen Harris, Eve Marder, Carol Barnes, Martha Constantine-Patton, Susan Goelz, Manfred Baetscher, Dana Aswad, Eric Nestler, Pietro DeCamilli, Tom Reese, Dan Johnston, Nelson Spruston, Ron McKay, Susan Catalano, Peter Seeburg, Hannah Monyer, Anne Young, Nancy Wexler, Barbara Wold, Judy Campbell, Pamela Bjorkman, Henry Lester, Kai Zinn, Marianne Bronner, and Leah Goentoro; most recently, they also include Regina Dugan, Marga Behrens, Bill Loomis, Tom Bartol, Terry Sejnowski, and Jost and Susanne Vielmetter. My four sisters and my brother—Beth, Janet, Nancy, Jean, and Tom—have been my secret weapon, providing me strength and sustenance when I most needed it.

Childhood

I was born in Pontiac, Michigan, in 1947 where my father, with a degree in educational administration, was a high school principal and my mother, although trained as an artist and teacher, was a homemaker. We lived outside Pontiac on Green Lake in a lovely house that my father built with a picture window looking out over the lake. When I was five years old, my parents’ family had grown to three girls, and his principal’s salary was no longer sufficient, so they moved to South Bend, Indiana, where my father opened a StrideRite shoe store.

My parents firmly believed that their primary parental role was to foster their children’s independence. They allowed us to explore the woods and fields around Twyckenham Hills, our suburban housing development, at will, and to find our own friends among our schoolmates and the many children who gathered at the community pool in the summer. I now realize that this early independence gave me a self-confidence and inner strength that served me well in my later career. Indeed, I would not have survived as a scientist without it.

In the 1950s, the Catholic grammar school that I attended taught “reading, writing, and arithmetic” well, but there was little education about science. Nonetheless, I became fascinated with the plants and creatures that I encountered in the woods and found library books to learn about them. At the age of about 10, I announced to my friends at the pool that I wanted to be a naturalist when I grew up. The older children politely told me that they didn’t think that was a job. A naturalist was a person who walked naturally and talked naturally. Undaunted, I found an advertisement in a comic book that promised a microscope as a prize for selling a certain number of flower and garden seeds. I wrote away for the seeds and went door to door trying to sell them. I was not an outgoing child, and this task soon exhausted me. I had not specified flower seeds, and so I had a large number of vegetable seeds to sell in a neighborhood where home gardens were nonexistent. Tired of hearing me complain at the dinner table about not being able to sell the vegetable seeds, my father finally told me that he had found a “farmer friend” who would buy the seeds. I protested, but he assured me that this was true. The microscope was delivered, and I reveled in finding tiny creatures in ground water. This early curiosity, one could say passion, drove my interest in science. The passion was internal, and I can’t point to any family history or single event that ignited it. I will add, though, that the seed-selling experience engendered a strong disinterest in business and selling, which persists to this day.

I attended St. Joseph’s High School, a Catholic school across town near University of Notre Dame and run by the Holy Cross religious order. (Yes, this is the same high school attended by 2020 democratic presidential candidate Pete Buttigieg three decades later.) The classes were uneven in quality, but many were taught by student teachers from Notre Dame and were excellent. These included stellar courses in English literature and composition, an excellent introductory course in biology, and an “enrichment” course in mathematics during the summer at Notre Dame. During the years I was there, St. Joe was “co-institutional,” meaning that girls’ and boys’ courses were taught separately in separate wings of the building. After-school activities and lunch period were “mixed.” The only physics course was offered by a religious brother (the male equivalent of a nun) on the boys’ side. In a sign of changing mores (this was 1968), several fathers of girl students (including mine) went to the men’s and women’s principals and informed them that it was not acceptable that girls were not offered a physics course. Unfortunately, the physics teacher informed them that he did not want to teach girls. This was my first introduction to the unique machismo associated with the discipline of physics. So, instead, the school offered to arrange for girls to take their physics courses at local public schools in the last period of the day. Attending this course would have meant that I couldn’t participate in any of the after-school activities. I was a cheerleader; so I declined the offer rather than give up cheerleading.

This segregated high school education had undeniable psychological effects on me and on the other girls. I believe that our teachers were committed to offering the best possible education to girls as well as boys. Fortunately for me, the classes at St. Joe, at that time, were “tracked” according to perceived academic ability. I was placed into college prep courses, populated, presumably, by those who tested well or had high grades. Whatever one might think of this practice now, it meant that I received a high-quality education (except in physics). However, by my senior year, I realized that many of my male friends, mostly also in “college-prep” courses, had internalized a notion of male dominance that made me uncomfortable. I was a pretty teenager and was often pressured for dates with maneuvers that I now understand were meant to demonstrate this dominance. I kept a distance from such behavior. However, in my senior year, I finally found a boyfriend whom I could talk to easily and who respected my intelligence. When his male peers discovered that we were an item, he was awarded a “lumber-jack shirt” for his “achievement” by a group that called themselves the “steady-fist club.” (The idea was that their outstretched fists remained steady until they had kissed a girl.) This embarrassed him and even made him angry. We remained a young couple for two and a half years until his growing interest in religion, and my alienation from religion, led us to break up.

One last anecdote from this period of my life involves a conversation at a high school reunion that took place about three years after I graduated. A tall, pleasant young man whom I had known slightly struck up a conversation and asked me what I was planning to do after college. I said that I was going to attend graduate school in biochemistry. He smiled, looked down at me, and said, “Better be careful, no-one will want to marry you.” I have never forgotten that. It was the first time I began to think that marriage might not be such a good idea for me.

College

I was faced with a difficult choice when I was admitted to the Unified Science program at the University of Michigan. My new boyfriend was going to attend Notre Dame, which at that time didn’t admit women. I was also admitted to St. Mary’s College, the girls’ school across the road from Notre Dame. I had a starry-eyed impression of the University of Michigan because my mother had gone there; however, at the last minute, I decided that I didn’t want to be that far away from my boyfriend, so I enrolled at St. Mary’s. My parents found a way to pay for me to live on campus beginning in my sophomore year.

Fortunately, St. Mary’s has a well-deserved strong reputation as a liberal arts college. In retrospect, my preparation for later graduate work at Hopkins was strong. When I arrived at St. Mary’s, it had just become possible for “St. Mary’s girls” to major in physics by taking the advanced courses at Notre Dame. I decided to try a physics major because, I think, the denial of physics courses in high school made me anxious to try it when the opportunity arose. An incident in my sophomore year, when I took the first major’s course in classical mechanics at Notre Dame, illustrates once more the atmosphere I faced as a young girl studying science in the mid-1960s. I enjoyed the mechanics course; the professor was a good teacher and supportive of the two girls who were enrolled in his class. I studied hard for the first test and worked together with some of the young men in the class to do homework problems and prepare for the test. The draconian practice at Notre Dame at that time was to post all the students’ grades outside the door of the class after each test. When the grades were posted, I found I had scored the highest grade. Of course, this should have been a happy occasion. However, one of the young men with whom I had studied said to me, “Well, I’m not going to help you anymore.” Again, that remark was seared into my memory. It is a perfect example of the negative feedback for a positive achievement that I would experience often in my career. I realized that I would be quite intellectually isolated if I majored in physics by taking the Notre Dame classes. This incident, together with a bewildering course in quantum mechanics, also at Notre Dame, soon sent me happily back to work on a chemistry major at St. Mary’s.

Most of the chemistry professors at St. Mary’s were exceptional teachers. The advanced classes and labs were small, numbering perhaps 10 students. I loved learning the science and came away with a strong grounding in organic and physical chemistry, along with supporting courses in mathematics and genetics. Though I will never know for sure, the small size of the classes at St. Mary’s might even have given me a better preparation than would the larger, more diverse classes at Michigan.

The curriculum at St. Mary’s included a set of rigorous courses in English literature, philosophy, history, and languages. Critical reading and writing skills were emphasized in all of the classes. I have never regretted taking the time to acquire a liberal arts background. It gave me a broad perspective and has enriched every aspect of my life.

My nonacademic life at St. Mary’s was more complicated. This was the late 1960s. The Civil Rights Movement had just culminated with the passage of the Civil Rights Act of 1964, the Vietnam War was heating up and young men of my age were being drafted. I had a strong interest in the public sphere and took my role as a citizen seriously. By my junior year, I had parted ways with my high school boyfriend and was spending time with a relatively small group of students at Notre Dame and St. Mary’s who actively opposed the war. While a few professors supported and encouraged us, we found ourselves in political conflict with many professors and other students. The fraught atmosphere of that time pervaded my college and graduate school years until the war ended. Because I was able to articulate political arguments clearly and easily, I often became an impromptu spokesperson. Many professors and administrators interpreted my words as intolerably brazen. On the one hand, these experiences deprived me of a significant portion of a socially comfortable young adulthood. On the other, they taught me how to fight for social change and honed a toughness that would stand me in good stead in my later career.

The Summer of 1969

In my junior year near the beginning of 1968, I began a relationship with a Notre Dame senior who was a student activist majoring in political science. Like many in that generation, he was wrestling with his own political views and what he wanted to do with his life. He moved to Georgetown to study for a degree in foreign affairs and soon joined the local chapter of Students for a Democratic Society (SDS), which was the foremost student organization opposing the war. We kept in touch and I visited him through my senior year and his first year of graduate school.

1968 was a turbulent year on most college campuses. I was passionately opposed to the war and traveled to Washington, D.C., to attend large “Mobilization” anti-war rallies. I also traveled to attend national meetings of SDS with my boyfriend, getting to know the other members of the “Washington D.C. collective.” These were interesting, even somewhat bizarre experiences. The SDS leadership in Chicago had begun to explore far-left “revolutionary” ideologies. I watched, with what I now realize was scientific detachment, as individuals like Bernadine Dorne and Bill Ayres debated which ideological “line” was correct. I remember one meeting in a rural setting in which young people strutted across a stage, one after another, debating whether SDS should “take up the gun.” In one vivid memory, I was riding on the passenger side of a car driven by my boyfriend with rain sliding off the windshield wipers. He asked me what I had thought about the discussion of “taking up the gun.” I answered that it seemed to me the problem was that even if their wildest dreams came true and one million people took up the gun with them, there would be one hundred ninety-nine million people shooting back. He answered, “Well, see you’re just a liberal.”

By the end of my senior year, my boyfriend had “broken up” with me for another SDS member, but I had accepted a graduate school position in the Biology Department at Johns Hopkins and I wanted to maintain contact with the other individuals in the Washington collective. Most of them were not interested in fomenting violence, but rather wanted to live and work in the poorer “working-class” communities and try to find a way to organize them to oppose the worst excesses of capitalism. I felt a commitment to remain in touch with their political movement, but I was also still committed to becoming a scientist. It seemed to me (naively) that I could be a connection between the scientific community and the left-wing student movement. These dual commitments led me to live for the summer before starting graduate school in a collective house with a group of SDSers from Washington who had decided to move to Baltimore to establish a movement there. Baltimore was still quite rigidly segregated; we moved into a row house in west Baltimore in the middle of a poor white neighborhood. The idea was to get to know our neighbors. I was much too introverted to do this well, and I recognized immediately that the neighbors thought we were quite odd. By the end of June, it was clear that I should get a summer job to help contribute rent and food for the group. I answered an ad and applied to work in a plastics factory in northwest Baltimore, using my real name. I did not mention my education beyond high school. On my first day, the foreman asked me solicitously why I wasn’t going to college. (I realize now that he could tell right away that I was not from the same Appalachian background as most of the other workers.) I replied that my father wanted me to go to college, but I didn’t like to read. He replied very kindly that I could major in something like chemistry. To this day, I don’t know whether he knew my actual identity and my plans to attend Hopkins in the fall. This was well before the internet was invented, so a search of my name would have been difficult. He remained friendly and fair during my time working there.

My job was to work with others at various stations to assemble plastic trees for toy electric railroad train sets. We would be given a pile of cast tree trunks with wire branches, dip the wires into molten plastic and then roll them in brightly colored small foam shapes to mimic leaves. I didn’t discuss politics at all, but rather approached this as a learning experience. One of my favorite co-workers was a middle-age Appalachian lady named Lily. She chatted happily with me as we worked. She learned that I was 21 years old and asked about my husband.

When I told her that I wasn’t married, she looked genuinely surprised and said, “You’s twenty-one and you ain’t never been married?”

Before I could answer, the assistant forewoman, Hatty, who didn’t want Lily to hurt my feelings, shushed her and said, “Now, Lily.”

Lily answered, “Hell, Hatty, Ah didn’t mean nothin’. If Ah ‘uz twenty-one and knowed what Ah know now, Ah wouldn’t be married neither!”

By the end of the summer, most of the workers seemed to accept me. When I confessed, just before I quit, that I was leaving to go to graduate school at Johns Hopkins, they seemed incredulous. Hatty just nodded knowingly, as if to say, “Sure. Sure.”

My commitment to the student movement, and my time living in West Baltimore, set the stage for my nonacademic life at Hopkins. I maintained my ties with the anti-war, left-wing student movement throughout my time in graduate school, although I quickly found the student movement at Hopkins and became less directly involved with SDS.

Graduate School

My years in graduate school, from the fall of 1969 through the summer of 1975, were truly “the best of times and the worst of times.” I loved the academic work in the vibrant Biology Department on the Homewood campus of Hopkins and later in the Biochemistry Department at the Medical School. The coursework was exactly what I was looking for, preparing me to study the molecular mechanisms of individual cells, the basic units of life. As I entered graduate school, I had a strong interest in studying the cells of the nervous system, which enthralled me with their power and complexity. However, interdisciplinary study of “neuroscience” was still very new. I was advised to get a strong foundation in biochemistry to prepare me for later more specialized research. This seemed sensible to me. I still have the large blue cloth binders that I filled with detailed notes about “biochemistry and biological oxidation,” “carbohydrate chemistry,” and mechanisms of “gene expression,” which were still mostly mysterious at that time. I took an optional course in advanced organic chemistry to better understand the chemical reactions of enzyme catalysis and metabolism, and a rigorous course in biophysical chemistry, which was actually an introduction to the young field of X-ray crystallography and the study of protein atomic structures.

In those years, the fields of biochemistry and cell biology were sufficiently cohesive that the Biology Department at Homewood held monthly evening symposia at which each of the faculty presented their latest work; their principal aim was to educate the graduate students. These were held in a large well-lighted hall with tiered seats facing a lab bench and blackboard. Saul Roseman was chair of the department and a leader in the study of membrane transport. Like most basic mechanisms, transport systems were first worked out in bacteria from which the constituent enzymes could be purified and studied in detail. Roseman’s lab discovered and elucidated the enzyme system responsible for adenosine triphosphate (ATP)-driven sugar transport in E. coli (the “phosphotransferase system”). I clearly remember his evening presentation in my first year. He began by explaining that there are two kinds of scientists. One kind wants to posit simple models that might account for a given cellular process, and then design experiments to test whether the model might be correct. The other kind believes that “No biochemist is smarter than an E. coli cell.” This statement had a strong influence on me. He was emphasizing that the best approach is often to let experiments guide your conceptual models of cellular mechanisms in a highly fluid manner. Saul Roseman was a brilliant teacher. He showed us how to see the meaning and the limitations of data. I recall another time after a class in which we had examined the classic papers of Hodgkin and Huxley on the ionic basis of the action potential. One of the students insisted that those papers showed definitively the mechanism underlying the action potential. Roseman said, “No, what does that data actually show?” I realized that he wanted us to see that the data showed only the kinetics of the voltage-dependent fluxes of sodium and potassium ion across the membrane, but not the underlying protein mechanisms. When I said so, he answered, “That’s right.” It was many years later that biochemists, including Bill Catterall and Rod MacKinnon, demonstrated how the movements of transmembrane voltage-dependent ion channels generate action potentials. I gradually found that the questions that interested me most involved the intricate systems of protein mechanisms that underlie cellular function. These hours spent learning how to think about biochemical experiments were “the best of times” for me.

At the same time, the Vietnam War was spinning out of control and Walter Cronkite announced the infamous “body counts” every night during the evening news. These were “the worst of times.” History was unfolding around us as the Berrigan brothers led a draft resistance; Daniel Ellsberg, in an act of conscience, released the Pentagon Papers to the Washington Post; Cronkite began reporting that the nightly “body counts” were generally considered to be unreliable; and we all knew that the war was a disaster and our government was lying to us about it. I somehow found time to affiliate myself with the student movement on campus, and with a loose confederation of left-wing groups in greater Baltimore that opposed the war.

I will relate a few vignettes that illustrate the flavor of my activism during the first three years of graduate school (1969–1972). One of my lab rotations in the first year was with Dr. Doug Fambrough. I chose his lab because I was already interested in neurons and neuroscience. In the nearby affiliated Carnegie Institute, he was studying the cell biology of neuromuscular development and was affiliated with the Biology Department. I started out learning such basic procedures as how to measure protein concentration by the Lowry method. I was given a small desk in the lab and personalized the space by putting some pictures and newspaper clippings on the wall immediately in front of it. One of these was a clipping from the Guardian newspaper showing a five- by three-inch picture of Ho Chi Minh with a poem titled “Poem from Prison” below it. (Ho Chi Minh wrote dozens of poems in prison. I don’t remember which of these it was; the poems usually expressed his love of the countryside of Vietnam and his desire to be free to help his people.) After a few days, Dr. Fambrough came to my desk and asked me, “Who’s that ugly face?” I answered with a smile that it was Ho Chi Minh. He said that I should take it down because not everyone in the lab was against the war, and he didn’t want politics in the lab. I took it down, but then thought about it overnight. I realized that if I allowed myself to be censured at this stage of my career, the compromising of principles might never end. The desk space was, after all, assigned to me. I put the clipping back up. The next day, I found it taken down and put into my top drawer. I put it up again. The next day, Dr. Fambrough came to my desk and told me that it would be best if I found another lab to work in. I said that was a good idea. It was easy to move to another lab because I was still a first-year student and because several faculty members were more sympathetic to the anti-war movement than Dr. Fambrough. I recount this incident because it later became well known, in an exaggerated form, in the small neuroscience community surrounding the Harvard Neurobiology Department, which I later joined. I think it was spread by Paul Patterson whom I met later in my graduate career. Zach Hall once told me, with great amusement, that he had heard that I had put a poster of Mao Tse Tung on the lab refrigerator. That didn’t happen.

At the beginning of my second year, the anti-war movement was at its peak and there had been a short but tumultuous student strike at the undergraduate Hopkins (Homewood) campus after the invasion of Cambodia in May 1970, demanding an end to military recruitment on campus. After a vote of the student body, military recruitment was ended, but only briefly. It was later reinstated after congress banned military spending at universities that didn’t allow military recruiting. Later in June, in a display of hubris (as I judge looking back), the Hopkins SDS chapter decided to protest the sizable investment of the Hopkins endowment in South African Krugerrands. The Apartheid policy had not yet ended and there was a national movement for divestment in South Africa. It was mid-summer and many of the undergraduates had left campus, so the remaining students decided to stage a sit-in at the meeting of the governing executive committee of the university that was occurring on campus. A group of about 20 of us somehow opened the door of the meeting room, filed in, and sat down on the floor around the perimeter of the boardroom. Someone announced to the committee why we were there and what we wanted (divestment in South Africa). Needless to say, the committee was not pleased. Eventually, after stating our concerns, and after an angry dialogue, we left the room. The president of the university at that time was Lincoln Gordon, who had been an ambassador to Brazil under Presidents Kennedy and Johnson. He was fed up with student protests and ordered a faculty “trial” to decide how to punish those who had “invaded” the executive committee meeting. I have a few clear memories from this “trial.” The faculty members picked as “judges” sat in front behind some tables and appeared intensely uncomfortable (head down, chairs pushed away from the table). The proceedings were recorded by a male court reporter on a small steno machine. Near the end, the student chaplain, Chester Wickwire, gave a short speech lauding the social consciences of the students and recommending no disciplinary action. Wickwire was eloquent; at the end of his speech, I recall clearly, the court reporter took his hands off the steno machine and clapped. I found this moving. In the end, the faculty judges recommended no disciplinary action. However, Dr. Gordon was not satisfied with this recommendation and decided to suspend all of us for the summer academic period. For the undergraduates, this had little consequence. I was one of the few (perhaps only) graduate students who had participated. The consequence for me was that I lost my student housing for the summer, and I technically couldn’t be paid a stipend or work in a lab for the summer. The faculty quickly figured out how to circumvent this problem for me. A history professor let me stay in a guest bedroom in his large home for the summer. I had met, and briefly dated, Paul Patterson who was a fifth-year graduate student working in the Medical School Biochemistry Department. His adviser, Dr. William Lennarz offered to have me rotate in his lab for the summer and eventually arranged to pay me after the summer ended. I remember Saul Roseman telling me in his chair’s office that “he didn’t know what I was doing for the summer.” It was clear that he meant that he would not reveal that I was working at the medical school. I also remember Roseman quoting Thomas Jefferson to me, saying something about listening to the young people. Eventually, I decided to do my thesis work in the Lennarz lab and switched to the Medical School graduate program after my second year.

Another incident while I was still rotating at the Homewood campus, is worth retelling in the age of “Me, too.” Because of my interest in neuroscience, I wanted to see how electrodes were used to record electrically from individual cells. A professor in the Carnegie Institute was routinely recording electrical signals from individual heart cells in culture. I asked if I could observe a recording session. He agreed and told me to come by late one afternoon. I detected something a little strange right away as he hovered over me while I was looking through the microscope. It was raining that day. After the recording session, he offered to drive me over to my dorm, which was a few blocks away. He put his hands on me as he helped me with my raincoat. When he parked his car at my dorm and got out of the car with me, I became quite uncomfortable. He asked if I wanted to get some coffee in the graduate student cafeteria on the ground floor. After we had coffee, he followed me up to my room. At this point, I knew what was happening. He followed me in the door. I sat in a single chair in the living room and he sat on the couch. He began talking about how we had a “chemistry.” He was rather insistent about staying. Finally, I stood up and told him that he should “leave now,” which he did. I was later told by a friendly faculty member that this same professor had stated in a faculty meeting about graduate students that I was spending too much time on “political stuff.” The faculty member told me that this was inconsequential for the moment, but wanted me to know who had said it. The friendly faculty member didn’t know about the incident in my dorm and I didn’t tell him. In retrospect, I’m grateful for the strong sense of boundaries and relative fearlessness that my parents instilled in me, and that I believe my Celtic heritage reinforces, because they allowed me to stand up to the offending professor.

The four years (1971 through 1975) during which I carried out my thesis work in the Lennarz lab were occupied with research on lipid metabolism in Bacillus subtilis. I learned fundamental procedures of biochemical research and experimental design. I also benefited enormously from the weekly journal clubs that were held in the department and for which attendance was mandatory. Learning to read, interpret, and present original research papers was at the center of my education in these years.

At the same time, I lived in a large community of leftist and feminist young people, living in the typical Baltimore row houses near the Homewood campus. During these years, the feminist movement was changing women’s thinking throughout the country. In my community, I participated in “consciousness-raising groups” in which groups of women from different backgrounds shared experiences, worked through problems and read books together. I also participated in a small leftist reading group in which we read some of the fundamental “radical” literature, ranging from the Port Huron Statement (an idealistic statement of goals written by Tom Hayden at the forming of SDS) to the Communist Manifesto. When I had time, I went to demonstrations and teach-ins sponsored by various political groups. I was never a leader in these groups because my first priority was still my graduate work. However, these groups formed my social life and taught me how to be a political activist.

I recall one of the more exciting events, which illustrates the prevailing issues and tumult of these times. Someone at the Homewood campus, perhaps the chaplain, Dr. Wickwire, had gotten word that the Baltimore police planned to raid the home of some of the leaders of the Baltimore chapter of the Black Panther Party. A few years earlier, Fred Hampton, a leader of the Chicago Black Panther Party had been killed in his bed, along with several others, during a raid by the Chicago police and the Federal Bureau of Investigation (FBI). The students were determined that we would not allow this kind of night-time murderous raid to happen “on our watch.” The Baltimore Black Panther house was located in the largely black residential area north of the Medical School campus. A large group of us decided to sit on the sidewalk outside the Panther house beginning in the early evening and staying through the night to prevent an attack on the Panthers. Someone cleverly decided to post a few students in parked cars on the routes that the police cars might use. They were to begin honking if they saw police cars approaching. I have a few clear isolated memories from that night. One involves hearing the sound of honking long after dark that warned us that police were approaching. I remember seeing two police cars pull up about a block and a half away from us across a vacant lot. Officers opened the trunk of one the cars and in the light from street lamps I saw them remove two large rifles from the trunk and hold them up high in front of them. I stood up and moved to the edge of the group near the street where I could be seen. I was wearing my usual “uniform” consisting of a green surplus army shirt and jeans. At the time, I had long dark blonde hair and looked younger than my 23 years. A bit later, I recall seeing a police car move slowly down the street passing our gathering. The police chief, a familiar face to all of us, stared gloomily out the window of the back seat and looked right at me.

It is interesting to me that I felt no fear at that time. I felt pride that we were able to put our “white privilege” in the way of what could have been another tragic killing. I knew that the police were not going to shoot past a person that looked like me. The raid was apparently called off and all of the police cars left. Dr. Wickwire told us later that the police chief had chastised him for bringing all these young Hopkins kids into such a situation. I don’t know whether any legitimate arrests were ever made. I do know that there was no shoot out. I believe the attention we brought to the situation may have caused the police to act with more caution. Several years later, in 1982, after a series of legal actions that went back and forth from district court to the 7th circuit court, to the Supreme Court, and back to district court, relatives of the murdered Chicago Black Panthers were awarded a total of 1.8 million dollars in damages. These law suits and others revealed illegal spying on Black Panthers and liberal student activists by J. Edgar Hoover’s FBI in an elaborate and now infamous operation called COINTELPRO.

As I was finishing the last year of my thesis work, I arranged a postdoctoral fellowship with Dr. Edward Kravitz in the Harvard Medical School Neurobiology Department. I knew about this unique department because Paul Patterson had done his postdoctoral work there with Drs. Furshpan and Potter and subsequently had become a junior faculty member. After defending my thesis, I moved to Boston during the summer of 1975, driving a U-Haul to a group house in Woods Hole, on Cape Cod, rented by the Kravitz lab members. Ed and his lab were leading a portion of the summer course in neurobiology at the Woods Hole Laboratory.

Harvard Postdoc (mid-1975–1978)

The transition to the Neurobiology Department felt magical to me. I had long wanted to study the biochemistry of nerve cells and finally would have a chance to do so in the renowned Harvard Department. This interdisciplinary department was the first of its kind in the United States, perhaps in the world. It was founded by Dr. Stephen Kuffler, a pioneering cellular electrophysiologist, and its other senior members included Drs. Hubel and Weisel representing systems neurophysiologists; Drs. Furshpan and Potter, developmental cellular electrophysiologists; and Dr. Kravitz, an invertebrate neurochemist. Junior faculty members in each of these disciplines and in neuroanatomy were added gradually, including many future leaders of the newly integrated field of neuroscience; Zach Hall, Story Landis, Paul Patterson, Ann Stuart, Ursula Drager, John Hildebrand, and Simon LeVay. Similarly, the list of students graduating from the department reads like a roster of leading figures in neuroscience. The magical feeling was accentuated by the ambience of Woods Hole, located on Vineyard Sound at the base of Cape Cod. The Marine Biological Library on the Woods Hole Oceanographic Institute campus is a repository of original work on marine species many of which have become model experimental systems for the study of nervous systems. It is also a quiet space where one can hide away and study in one of its many cubicles.

At the end of the summer, we moved back to the Harvard Medical School labs on Longwood Ave. Ed’s lab worked on the lobster nervous system, focusing on discovering the identity and roles of neurotransmitters in the large identifiable neurons in lobster ganglia. Ed’s early work had established the inhibitory role of gamma-aminobutyric acid (GABA) in the lobster nervous system. When I arrived, he was focused on understanding the biochemistry and actions of the biogenic amines octopamine, dopamine, and serotonin, which are secreted into the lobster hemolymph by specific neurons and appeared to play a modulatory role in the nervous system. Ed patiently taught me to use a dissecting microscope to remove lobster ganglia and leg nerves and prepare them for experiments. Because of my background in organic biochemistry, I was assigned to determine how the biogenic amines were inactivated and metabolized after they were released. For the first several months, applying my expertise in this way seemed a reasonable trade-off for the feast of new learning that I enjoyed as a member of the department.

The postdoctoral fellows from all the labs met weekly for “shadow” reading sessions in which we studied the course material and original papers that made up the department’s graduate courses. This curriculum was brilliantly organized and included critical reading of a series of original papers by Hodgkin and Huxley, Bernard Katz, Ricardo Miledi, and others, covering the electrophysiology of axons and synapses. I also read early papers describing the cellular and subcellular anatomy of the brain, which I found particularly fascinating, and I developed a strong curiosity about the molecular composition of the various structures that could be seen within synapses in the electron microscope. We studied papers of Hubel and Wiesel in which they used extracellular single-cell recording in the visual cortex to map out the receptive field properties of neurons in the cortical layers, including ocular dominance columns, work for which Hubel and Wiesel would eventually be awarded the Nobel Prize. During the time that I was in residence, Hubel, Wiesel, and Simon LeVay were working out the physiology and anatomy of “orientation columns” in the visual cortex. Because the understanding of neuronal biochemistry was still quite rudimentary at this time, reading in this area included mostly papers about the properties of basic neurotransmitters (glutamate, GABA, acetylcholine, peptides, and biogenic amines) and Dale’s principle, which held that each neuron synthesized and used only one transmitter. We now know that Dale’s principle is an oversimplification and that many neurons release both a “major transmitter,” such as glutamate, GABA, and acetylcholine, and a modulatory “co-transmitter” peptide or biogenic amine. The nature of the acetylcholine receptor at the neuromuscular junction was still unknown; indeed, some still speculated that it was not a protein at all but rather a configuration of lipids that was perturbed by release of acetylcholine.

The two and a half years that I spent in the Kravitz lab and the Harvard Neurobiology Department offered the richest and most dense learning experience of my life. I moved into a shared house with Marge Livingston, Josh Sanes, David Furster, and Charlie Gilbert, all of whom became major figures in the neuroscience community. We shared many meals and stimulating conversations. Socially, I dated Eric Schwartz, a retinal physiologist, from whom I also learned a great deal. In my research, I succeeded in showing that octopamine, dopamine, and serotonin were inactivated by two processes in the lobster bloodstream, β-alanine substitution at the amine group, and sulfation of the ring hydroxyl groups. I believe that I also contributed to the biochemical sophistication of the members of the department through various group presentations. I particularly remember being proud of a presentation that I made on Peter Mitchell’s “chemiosmotic hypothesis” for ATP synthesis in mitochondria, for which he was soon awarded the Nobel Prize in 1978. This mechanism is now, of course, standard textbook fare. In 1977, however, it was just becoming accepted.

Unfortunately, despite all that I was learning, I became increasingly anxious about my future because I knew that I wanted to be prepared to investigate more fundamental biochemical processes, such as synaptic regulation, and I increasingly felt that I wanted to work in a mammalian system. I had been trying to arrange a project in Dr. Wiesel’s lab with Charlie Gilbert to identify neurotransmitters in the retina. Charlie seemed to agree to this project, but then began it with no communication with me. When I objected that I would like to be included in the planning for the project, he became angry and it was clear that the collaboration would not be possible. I wasn’t able to find a way to satisfy my research desires within the neurobiology department and eventually left on a somewhat sour note. Around the same time, I had become interested in the work of Paul Greengard, who was beginning to study regulatory protein kinases in the brain. This field was in its absolute infancy but seemed promising because of the important role that protein phosphorylation had been shown to play in glucose metabolism in the liver and heart. In early 1978, Josh Sanes, who had been an undergraduate student in Dr. Greengard’s lab at Yale, invited him to give one of the lunch-time seminars that were an important part of the intellectual life in the Neurobiology Department. I spoke with Dr. Greengard after his talk, and he immediately responded to my interest in his work. A few months later, he returned to Boston and invited me to dinner. In my very unsettled state, Dr. Greengard’s interest became a possible salvation. Thus, began an association that both defined my future career and later badly damaged it.

Yale Postdoc (1978–1980)

In 1978, I was a relatively naive and rather unhappy 30 year old, looking for a way to work in a mammalian system on neuronal biochemical mechanisms, a field that I loved. Therefore, the attention that I received from Paul Greengard was like warm sunshine after a cold rain. It soon became apparent that his interest was both scientific and romantic; at least that is how I saw it. He was a charming man, when he chose to be, and I was completely hooked. We spent a great deal of time talking about his research and about neuroscience, in person and on the phone, but also began spending an equal amount of social time together in the last few months of my time in Boston. I knew that he was married, but rationalized that his wife, whom I later came to like very much, appeared to me to be preparing herself to leave the relationship. When I was unable to find a satisfactory position in the Harvard Neurobiology Department, Greengard agreed that it seemed logical for me to move to his lab to do a second postdoctoral fellowship. I had little experience to prepare me for the problems that can arise when one is involved in a personal relationship with one’s mentor.

I was very good at hiding the personal side of my relationship with Dr. Greengard from those in his lab. I found a nice apartment and maintained a normal social life with my peers, making time for trysts with Greengard when he traveled or when his wife was away. I often visited museums with him and very much enjoyed learning from his cultural experience as well as scientific conversations. Looking back, I realize that this affair offered me a widened view of both the scientific and cultural world that would not have been available to me otherwise. Intense intellectual relationships between men and women easily lead to sexual attraction, and are too easily disrupted by it, especially when the attraction is not mutual. As a result, in a male-dominated profession, women are often denied access to the kind of ongoing, informal intellectual exchange that occurs naturally among male mentors and students, and even among male peers. To this day, I don’t believe that anyone in the Greengard lab knew of our personal relationship. Indeed, I told no one about it, and it remained hidden. A few in the lab seemed to notice that I appeared to be a “favorite” and, I think, resented it. For the most part, I got along well with others in the lab and acquired several life-long colleagues and friends.

In the 1970s, the National Institutes of Health (NIH) were well funded and laboratories like Greengard’s at Yale were large and amply supported. Ten to twelve postdocs, three or four students, and several technicians were crowded into a suite of five laboratory rooms and offices surrounding a walk-in cold room, instrument rooms, and larger offices for Dr. Greengard and his secretary. I arrived in the lab after postdoc Howard Schulman had published two papers establishing the presence in rat brain homogenates of a calcium-dependent protein kinase activity that depended on the recently discovered calcium-dependent regulatory protein (CDR, later named calmodulin). Many brain “substrate proteins” for this kinase activity could be seen as bands in the phosphate-labeled gels published in Howard’s papers. Calmodulin-dependent protein kinases had only recently been discovered in other tissues. Thus, Howard’s papers received a lot of attention. Howard had accepted a job as assistant professor at Stanford and Greengard wanted me to continue with the task of characterizing the brain calcium-dependent protein kinases. I readily agreed because this was exactly the kind of mechanistic research that most interested me, and I wanted to learn more about techniques of protein biochemistry and enzymology. At this juncture, I learned that Greengard had “forbidden” Howard to work on calcium-dependent protein kinases in the brain at Stanford, apparently believing that he somehow owned the field of calcium-dependent phosphorylation in the brain. This was my first indication of Greengard’s extreme territoriality about his scientific work and it seemed odd to me because there was so much to be done. At Stanford, Howard decided to investigate the role of calcium-dependent phosphorylation in regulating biogenic amine metabolism, and eventually, appropriately, resumed work on brain calmodulin-dependent kinases. I proceeded to develop an assay to measure phosphorylation of “protein I” (now known as synapsin I) by calcium/calmodulin-dependent protein kinase. I used the assay to fractionate distinct brain calcium/calmodulin-dependent protein kinases by chromatography, distinguished by their specificity for phosphorylation of different parts of the synapsin protein. The goal was to understand how many such protein kinases we could detect, and, eventually, how and where they carry out their regulatory roles.

I shared a small office with Dana Aswad, now at the University of California–Irvine, and Annette Dolphin, now at University College London. In a nearby room, Wieland Huttner and Pietro DeCamilli were working out ways to purify synaptic vesicles. They soon showed with cell biological and electron microscopic techniques that synapsin I is a peripheral synaptic vesicle protein. Susan Goelz, who became a close friend and later led the development at Biogen of the first biologic treatment for multiple sclerosis, worked in another of the Greengard rooms next to Eric Nestler, who was finishing up his thesis work. At that time, the Greengard lab was a seedbed for future leaders in research on neuronal biochemical mechanisms.

As I had done at Harvard, I worked six- and seven-day weeks in the lab, reading, planning procedures, and carrying out experiments to understand more about the molecular characteristics and specificity of brain calcium/calmodulin-dependent protein kinases. This pace of work was my own choice; I found it exhilarating to be able to focus completely on solving puzzles that I had been curious about for so long. Immersing oneself in scientific benchwork is, I suspect, rather like working in an art studio. I became oblivious to potential distractions because the creative process was intensely rewarding. After a year of work, I had identified two distinct protein kinases, which later were called CaMKI and CaMKII. CaMKII seemed to be the most abundant, so I focused on the trial-and-error process of purifying it by then-standard protein chemistry techniques. As I examined increasingly purified fractions, I noticed that two of the prominent brain substrate proteins, a doublet of 50 and 60 kDal proteins present in approximately a 2:1 ratio, co-purified with the protein kinase activity. I recognized this as a clue that these might be autophosphorylated subunits of the kinase itself, and I shared this possibility with the lab.

Just before I arrived in the Greengard lab, Dr. Phil Siekevitz’s lab at Rockefeller had published two important papers reporting the isolation and characterization of a subcellular fraction that he termed the postsynaptic density (PSD) fraction. It was prepared by centrifugation from synaptosomes after lysis and removal of lipids with mild detergent. Siekevitz et al. presented evidence that the fraction was derived from the dense structure seen at postsynaptic membranes in electron micrographs of the brain. The work was anchored in the tradition of George Palade with whom Phil Siekevitz had studied; and I found the papers to be elegant and convincing. Of course, many skeptics complained that the isolated structures observed by electron microscopy were simply nonspecific aggregates produced by the treatment of synaptosomes with mild detergents. However, I thought the structures were too regular to be completely nonspecific and I was excited because the method opened up the possibility of studying in detail the protein composition of this mysterious organelle. In 1980, Siekevitz followed up with a study of PSD fractions in different brain regions. His group had seen the Schulman papers, and they included an autoradiogram showing that the PSD fraction contained a calcium/calmodulin-dependent protein kinase. The two most prominent substrate proteins for the calcium/calmodulin kinase had the same pattern in gels as the two phosphorylated proteins that were co-purifying with CaMKII. Interpreting scientific data often involves pattern recognition. I began to suspect that a portion of CaMKII might be immobilized in the PSD fraction and mentioned this to the M.D./Ph.D student who had begun working with me. A few years later, she and Greengard would race to try to publish this finding ahead of my lab at Caltech.

In mid-1979, as I was finishing up the first project that I would publish from the Greengard lab, I was contacted by Jim Hudspeth, a professor at Caltech, who asked if I would be interested in applying for an assistant professorship at Caltech. I hadn’t yet applied for any faculty jobs because my research output was still small. However, I had presented my recent work at various meetings, and Jim had heard about me from former colleagues at Harvard where he had been a graduate student. At that time, the number of young people who had interdisciplinary training in biochemistry and neuroscience was still small and the Harvard Neurobiology Department was a popular source of new faculty in neuroscience. Caltech wanted to build its faculty in neuroscience having hired Hudspeth and David Van Essen, both of whom were graduates of the Harvard department. I felt this was an offer I couldn’t ignore, although I had never lived on the west coast and felt some trepidation about moving so far from family and friends. Greengard was cautiously supportive of my applying for the job. After a visit and a seminar, I was offered the job and eventually accepted the offer in early 1980, agreeing to start the appointment in January of 1981. I was convinced by the quality of the Caltech faculty, the beautiful campus, and the generous start-up package that would allow me to build my own well-equipped and well-funded lab.

In the months after I accepted the Caltech appointment, both the personal and the professional relationship with Greengard deteriorated. We were seeing much less of each other and I had begun casually dating postdocs from other labs. To my surprise, this seemed to enrage him, and he began criticizing my work in the lab and trying to insert new lab members into the work that I was finishing up. The most egregious problems occurred when I tried to discuss with him the work that I would begin at Caltech. I explained a few ideas that I had about related areas of investigation, but Greengard finally insisted that the entire field of protein phosphorylation in the brain was his field. I recognized this as an attempt to fatally wound my ability to begin a new lab on strong footing. I had come to his lab, bringing my expertise in neuroscience, to establish myself in the field of regulatory biochemistry in the brain. During one final discussion in the Yale lunchroom, I told him that since he didn’t seem to want to agree to any of the proposals that I had made, I would continue with the project I had been working on in the lab. I was passionate about the work, and I had come to the lab to enter that field. He stood up from the table in a rage and stalked off. The next months were unpleasant, but I finished enough work for a second paper, and wrote a grant that eventually was funded, enabling me to arrive at Caltech in January of 1981 with an NIH grant.

First Six Years at Caltech (1981–1986)

The six years of my assistant professorship at Caltech best epitomize “the best of times and the worst of times” that I alluded to earlier.

I arrived at Caltech in early January 1981, leaving New Haven after a snowfall. Mid-winter in Los Angeles means mild temperatures from 50 to 70 degrees and occasional rainfall. I remember seeing a lighted sign on the freeway reminding drivers to “Drive safely in winter weather.” Being a seasoned snow driver, I wondered what winter weather they were referring to, until I realized with amazement that it was the rain! Another immediate impression upon moving from the east coast was how clean the cities were compared with Boston, New York, or New Haven. In Pasadena, I found flowering trees along with tall palms and desert succulents. I rented an apartment near Caltech and started on my new job with no close friends or colleagues nearby for support. Thus, the first year was both exhilarating and lonely. I had designed the layout of my new lab myself, and it was finished by the time I arrived; the major equipment was already in place, installed by Bill Lease, the divisional equipment manager. My second-floor office, which I still occupy, has a large window overlooking a lily pond, jacaranda trees, and the administration building. I quickly began staffing the lab with a technician and students. During the first years, I also worked every day at my own bench. My first student, Mark Bennett, finished the purification of CaMKII and used biophysical measurements of its Stokes radius and sedimentation coefficient along with other biochemical measurements to show that the kinase is a dodecamer composed of alpha (50 kD) and beta (60 kD) subunits in a 3:1 ratio. This quantitative analysis has stood the test of time. We were lucky that Jeremy Brockes, who occupied a lab near mine, was an expert in methods to generate monoclonal antibodies with selected specificity, a technique that had been invented only recently. My second student, Ngozi Erondu, generated a high-affinity specific monoclonal antibody against the alpha subunit and used it to document the extremely high concentration of CaMKII in the hippocampus (2%) and cortex (1%), and lower concentrations in other brain regions. The three of us worked together to show that a 50 kD protein in Siekevitz’s PSD fraction, which he had termed the “major PSD protein,” was the alpha subunit of CaMKII. In 1984, I was invited to give a major talk at a well-attended symposium on calcium regulation in the brain at the annual meeting of the Society for Neuroscience. These first five years were happy ones in which I was able to build on the work I had started in New Haven and to teach bright young people, in the lab and in the classroom, about both protein biochemistry and neuroscience.

However, the wolves were gathering. I didn’t know, and didn’t think about, what was being pursued in the Greengard lab, 2,000 miles away. Our work on the presence of CaMKII in the PSD fraction was published in the Proceedings of the National Academy of Science USA in December 1983. Two months later, in February 1984, a very similar paper by Kelly, McGuinness, and Greengard appeared in the same journal. I knew that the fortuitous appearance of our paper in the last month of 1983, followed by his paper in 1984 would infuriate Greengard, who hated to be “scooped” even more than most of us. In the next few years, I would confront the perils of working in an interdisciplinary, male-dominated, and emotionally overheated field.

A third graduate student, Stephen Miller, began examining the possible effects of autophosphorylation on the enzymatic activity of CaMKII and soon noticed that after the two subunits became fully phosphorylated, the rate of protein kinase activity was somewhat reduced, but it was also independent of the addition of calcium or calmodulin. We first submitted the work to the Journal of Biological Chemistry, but we were told, correctly, that we needed to show that the effect of autophosphorylation was reversible by dephosphorylation by a protein phosphatase. Steve set out to do these experiments. In the interval, John Lisman visited Caltech from Brandeis to give a neuroscience seminar. He saw Steve’s work and pointed out, with excitement, that this property of the kinase might match a situation he had written about in a theoretical paper in which he postulated that such a kinase activity could “outlast protein turnover.” He thought that this situation might allow protein phosphorylation to encode long-term memories and was thrilled to hear about an autophosphorylating kinase located in the PSD. Steve eventually showed that protein dephosphorylation did, in fact, reverse the calcium-independent activity. We then proceeded to show that the autophosphorylation occurred essentially entirely within a single dodecameric holoenzyme and not between holoenzymes. This result disappointed John. Nonetheless, we had shown that several sites were phosphorylated, and we postulated that the resulting slow pace of dephosphorylation might allow the kinase to act as a kind of switch, maintaining its activity for a brief period of time after a transient rise in postsynaptic calcium had triggered the initial activity. Two minor dramas followed from this work.

The first involved a long delay in the review of our revised manuscript by the Journal of Biological Chemistry. While we were waiting to hear about the manuscript, I was invited to present the work at MIT. During the dinner after the talk, I mentioned that the revised work had been stuck in re-review at Journal of Biological Chemistry for longer than normal. I recall Professor Frank Solomon looking alarmed; he told me to pull the paper immediately and send it to Cell. It had not occurred to me that reviewers might be holding up the manuscript to allow someone else to submit the finding. At the time, Cell was a growing niche journal that I, correctly, thought of as a kind of club. However, I did as Solomon suggested and our paper appeared in Cell four months later in March 1986. To my amazement, a short paper from another lab reporting the same reversible calcium-independent activity after autophosphorylation, appeared in the Journal of Biological Chemistry three months after ours appeared in Cell, having been submitted in February 1986. The senior author of that paper was indeed a reviewer at the Journal of Biological Chemistry. Frank Solomon was wiser than I about what can happen with reviews in a competitive field.

This unsettling incident echoed another that had occurred during review of an earlier paper of ours in the Journal of Biological Chemistry, also authored by Stephen Miller, reporting purification of a cerebellar form of CaMKII and documenting a difference in its subunit composition. The paper was rejected for reasons that had little to do with its accuracy. Then a few month later, a very similar paper was published from the Greengard lab in the same journal. Steve was furious and completely disillusioned. I called the editor of the Journal of Biological Chemistry and asked how this could have happened. He checked into it and discovered that Ed Krebs had handled the review of both papers. Our paper was submitted three months later than the Greengard paper, which hadn’t yet appeared in print, so Krebs had rejected ours. The editor explained to him that this was not the correct procedure and told us that the journal would publish our paper as quickly as possible. A few days later, I received a call from Dr. Krebs, who apologized for the mistake. I will never know whether or not either of these two incidents involved deliberate reviewer misconduct.

The second minor drama was the reaction in the neuroscience community to the notion that CaMKII might act as a “switch,” as we suggested in the Cell paper. Before about 1970, the term neurobiology had referred to anatomical and electrophysiological studies of the vertebrate brain, nerve ganglia of invertebrates, or individual neurons. In 1966, Steven Kuffler established the interdisciplinary Harvard Department of Neurobiology that included physiology, biochemistry, histology, neuroanatomy, and electron microscopy in a single department. Kuffler was a visionary and he recognized that the field of biochemistry, which had its roots in microbiology, was on the verge of great progress in understanding molecular mechanisms in specialized cells of multicellular organisms. However, as is often the case in interdisciplinary fields, electrophysiologists usually had superficial training in molecular disciplines. Similarly, those trained in biochemistry and cell biology had often been taught to avoid studying the most complicated cells, and knew little about the most salient mechanistic questions in neurobiology. With my years of training in both areas, but principally in classical biochemistry, I was still a rare bird.

A prominent group of cellular electrophysiologists were studying the phenomenon of long-term potentiation (LTP), which they believed to be a substrate of memory formation. In the mid-1980s, the hypothesis that LTP was triggered by a transient influx of calcium ion into individual synapses through N-methyl-D-aspartate (NMDA)-type glutamate receptors was gaining favor. In our paper in Cell, we had discussed the mechanistic possibilities and limits of the switch-like behavior of CaMKII in the synapse in relation to synaptic potentiation. John Lisman began to talk about CaMKII as the memory molecule, and to my amazement, many neurobiologists lauded this idea. John even suggested to me that we should collaborate: he would be the theorist and I would be the experimentalist. That was a gross misperception of my intellectual stance. I still believed Saul Roseman’s maxim that “no biochemist is smarter than an E. coli cell.” Certainly, no scientist is smarter than a neuron! I knew that the mechanism we had uncovered, together with the abundance of CaMKII in the cortex and PSD, meant that CaMKII was likely an important player in mechanisms of synaptic plasticity. However, my previous training had taught me that biochemical mechanisms in cells are comprised of highly interconnected networks of reactions that provide flexibility in response to the environment as well as robust homeostatic adjustments. Surely, a function as critical to evolution as memory does not reside in the properties of a single enzyme. I believed it was much more important to probe the synapse, and the PSD structure, for the other proteins that are regulated by CaMKII, and thus to begin to unravel the biochemical network regulating memory formation. Most electrophysiologists were not primed to listen to this argument. It probably didn’t help that I was female, and that Paul Greengard had spread the notion that I had somehow stolen all my ideas from him. Unfortunately, the brief frenzy about CaMKII as the memory molecule led to some ugly scenes. For example, when Stephen Miller presented his work at a large meeting of the Society for Neuroscience in 1985, Professor Jimmy Schwartz stood up and berated him saying that he had already discovered this mechanism in Aplysia. He was referring to a recent paper from his lab that had been influenced by a discussion I had had with him at an earlier Cold Spring Harbor meeting. Schwartz had shown me an autoradiogram of proteins that were phosphorylated in a calcium-dependent manner within an Aplysia homogenate. It showed a prominent pattern resembling the alpha and beta subunits that we had identified in mammalian brain. I pointed to these bands and told him that they might well be the Aplysia CaMKII. No good deed goes unpunished. Schwartz apparently took this suggestion as fact; his student carried out some studies in the Aplysia homogenate and suggested that autophosphorylation might make the Aplysia calcium-dependent kinase “autonomous.” We cited his suggestion in our Cell paper, but only as a suggestion. No biochemist would consider studies on an enzyme in a protein mixture adequate to define such a mechanism. After all, we had appropriately been required to show that the calcium-independent activity of our purified kinase was reversible by a purified protein phosphatase! This incident was an example of the ill feelings that too often arise when two fields that converge in interdisciplinary work hold different standards of proof. I was offended by the notion that Schwartz would consider his experiments in Aplysia homogenates equivalent to our work with purified proteins. Schwartz’s work had appeared before our Cell paper was published, but after Miller had already shown in the lab the effect of autophosphorylation on pure CaMKII. Schwartz’s paper had had little influence on our thinking. Nonetheless, Schwartz and others at Columbia, including Eric Kandel, apparently continued to believe that I had somehow stolen Schwartz’s finding. Some months later, Schwartz wrote me a handwritten letter apologizing for his behavior toward my student Stephen Miller. Schwartz said that he had been “attracted to me as a woman” and had thought of me as a “guardian angel of his work,” so he was upset by our overlapping work. I am grateful for his self-insight; but it illustrates how fraught this overheated field was for any scientist, much less a young woman with an expertise that was not well understood by most neurobiologists.

Meanwhile, my student Mark Bennett had learned the basics of molecular cloning from Norman Davidson’s lab and sequenced the first full cDNA clone of a CaMKII subunit, the beta subunit, which we published in 1987. As the time approached for my tenure review, I believed that my lab had accomplished a great deal. And with the publication of the work on autophosphorylation and the cloning of the beta subunit, we had clearly differentiated ourselves from the Greengard lab. Unfortunately, my confidence in the importance of our good work and in the influence at Caltech of my reputation in the neuroscience community was overly optimistic.

Tenure Year

The saga of my tenure review at Caltech began with the formation of a tenure review committee in early 1986. The committee was formed six months earlier than normal. I assumed this reflected the fact that I had already accomplished enough to be awarded tenure. Instead, I later learned, Lee Hood, the divisional chair, wanted the decision to be made while he was on a sabbatical due to end in December 1986. The divisional chair was supposed to be neutral, and Hood, I was later told, wanted to be able to speak against me at the faculty meeting. Hood wanted the acting divisional chair, James Strauss, to preside at the voting meeting.

The chair of the tenure review committee was Mark Konishi, a revered neuroethologist who studied bird song. The assignment was difficult for him because he knew that my work had been important, but he had little depth in biochemistry himself. On the other hand, the two biochemists appointed to the committee had little knowledge of neuroscience. The entire process was mired in the chasm between the “molecular biologists” and the “neurobiologists” in the division. In the years leading up to 1986, the field of molecular biology had been burgeoning because of the introduction of genetic engineering in 1975. Similarly, neuroscience was becoming an interdisciplinary field and was also making great scientific strides. In several research institutions, there were struggles between the two fields for recognition and resources. At Caltech, this battle had grown nasty; the simmering war between them broke into the open during my tenure review.

The full story of the two-year process of my tenure review, in which an initial negative decision driven by a group of molecular biologists was reversed by the provost and trustees, would require a book. Here I will provide a few highlights and anecdotes that illustrate the flavor of this time for me. Because the issue very nearly entered the formal legal arena before it was resolved, I learned a great deal about the relevant, supposedly confidential, events that underlay my tenure review—much more than a young faculty member would normally come to know.

The report of the tenure review committee was submitted to the Biology Division in May 1986. It recommended my promotion to tenure, with one dissent by one of the biochemists. As the report was being prepared, I had been invited to apply for a tenured job at MIT and the faculty of their Biology Department had voted in favor of the appointment. We were awaiting approval of the dean. I was told that most of the 10 outside letters of recommendation obtained by Caltech were quite positive. A few were lukewarm, but none were negative. When my three year contract had come up for renewal in 1983, Paul Greengard had not been willing to provide a letter. Mark Konishi believed this was inappropriate on Greengard’s part, and he did not ask him for a letter regarding the tenure decision. The tenure committee was also aware of Dr. Schwartz’s complaints and so he was not asked for a letter. However, Eric Kandel from Columbia was asked for a letter and I’m told that he wrote that I had shown that CaMKII has two subunits. “Perhaps in the future she will be more creative.”

The meeting of the tenured Biology faculty to vote on my tenure occurred on September 20, 1986. In the meeting, Mark Konishi and his committee were surprised by an angry attack by Lee Hood, Eric Davidson, and other molecular biologists, and were not prepared for it. Lee Hood stated that he did not like me and resented that I had questioned him openly about certain fund-raising initiatives discussed earlier in the division. One of the molecular biologists stated that it was “no big deal” that I purified CaMKII from the brain because it is a “very abundant enzyme”—one of his students had purified a protein that represented only a few tenths of a percent of the protein in the tissue of origin. I recognize now that this demonization of my voice and the discounting of the importance of my lab’s work reflected a subtly misogynistic inability to recognize a female as an independent authority. These remarks offended the neurobiologists, all of whom supported my promotion to tenure and felt ambushed by the hostility. The meeting ended with a split vote and deep anger between the two factions of the division. There were enough negative votes a few weeks later that the Institute Academic Council, which consisted of the chairs of all the divisions, the provost, and the president, accepted the acting Biology Division chair’s recommendation that I not receive tenure.

Word of the controversy had reached MIT and the dean there refused to approve the appointment that had been voted on by the MIT Biology faculty. This news finally caused me to slip into what I now recognize was a reactive depression. I became unable to eat anything other than milk for a few weeks, and lost 20 pounds over the next few months. I knew the decision was unfair, and others from inside and outside the division told me as much. Mark Konishi and David Van Essen had submitted a memo of concern to the provost, mentioning, among other things, the personal animus brought into the discussion by Lee Hood. One department chair from another university told me that he thought the decision might be “actionable.” I didn’t know what that meant. He told me that it might be illegal under the provisions of the Civil Rights Act, which forbade employment discrimination on the basis of sex.

Here is where Caltech’s recent history came into focus. In 1977, the Humanities and Social Sciences Division had denied tenure to literature professor Jenijoy LaBelle. She filed a complaint with the Equal Employment Opportunity Commission, which investigated and found Caltech to have a “pattern and practice” of discrimination on the basis of sex and race. The Commission sued Caltech on her behalf, a particularly strong action. One of the most salient pieces of evidence was a comparison of her tenure case to the most recent male who had received tenure in the Humanities and Social Sciences Division. LaBelle’s case on paper was much stronger. Caltech settled the case, and LaBelle eventually received tenure. In the wake of this case, the trustees had admonished all of the divisions to make a better effort to hire women faculty. Indeed, my hiring in 1981 had been influenced by this mandate. Nevertheless, in 1986, Caltech had a total of only nine female professors (eight without me), 3% of the total faculty. I had been the first female hired in the Biology Division, a second had previously been hired in Chemistry and, after receiving tenure, was given a joint appointment in Biology. Thus, I was also the first female to undergo a tenure review in the Biology Division. These numbers meant that Caltech had among the lowest proportions of female faculty of all universities in the United States.

A friend of mine from the Jet Propulsion Laboratory, Robert Nelson, referred me to John McTernan, a Los Angeles civil rights and labor lawyer who had represented his father, a famous labor organizer, in a 1955 Pennsylvania Sedition Act case. In the midst of my depression, McTernan gave me invaluable help in organizing documents and information to construct a case. I clearly recall one early conversation in which he repeatedly asked me, “Why are you doing this?” I became annoyed because I thought the answer was obvious. Finally, I blurted out, “Because I think what they did was wrong and I don’t want to let them get away with it.” He smiled, and never asked me the question again. I later realized that it is important for a lawyer to clearly understand his client’s goals and also to be sure the client herself understands her goals. In some labor cases, the client actually wants a monetary settlement. In fact, the issue of a monetary settlement came up later at Caltech.

History has a long reach. People like McTernan have been devoting their lives to the legal preservation of civil liberties for a century or more. My activist history had prepared me to fight for my own rights in this situation.

The first crucial step was an appeal of the Academic Council’s negative tenure decision to the Academic Freedom and Tenure Committee (AFTC) within Caltech. As I emerged from the worst of my depression, I submitted an appeal in February 1987 outlining the sequence of events and the problems with the tenure process. Two of the members of this committee knew me from service on other institute committees. One of them later told me that he had kept careful notes for me to use later, if I needed them in a legal action. Both of them made sure that the incidents and procedural flaws that they believed were improper were all included in the report. The hearing of my appeal by the six member committee took several months. I, and the provost, finally received their report in early June 1987. It documented many irregularities in the tenure procedure, including instances in which the faculty handbook was not followed. It concluded that the committee could not say whether or not a perfect process would have yielded a different outcome, so they did not recommend reversing the decision. At this point, events moved into high gear.

Eleanor Searle, a senior history professor at Caltech, who had previously served as vice-chair of the faculty, had told me to bring her the report as soon as it was released. I remember putting a copy in a manila envelope and dropping it through the mail slot at her home because she wasn’t there when I arrived. I also gave her a copy of my most recent NIH grant review. Somehow, I had managed to submit the grant renewal several months earlier, and it had received a “priority score” at the 1.9 percentile, meaning that it was among the two or three highest scoring proposals of the 100 or so reviewed by the panel in that cycle. Eleanor had moved to Caltech from UCLA where she had served on the Staffing Committee. Thus, she had quite a bit of experience with tenure cases. She called the next day to say that the committee at UCLA would have been “falling about laughing” at the report I had given her. She believed that it was laughable that the AFTC had documented personal hostility and many flaws in the process and yet had not recommended reversing the case. She planned to talk to the provost about it as soon as she could, and she had given the material to a law professor from the University of Southern California (USC) who was visiting the Caltech Humanities and Social Sciences Division for the summer term. The law professor’s wife was a neurobiologist who told him that most researchers would kill for a priority score as high as I had received. The USC professor told Eleanor that he knew who should see this material. He brought it to Judith Resnik, a professor at USC law school who had recently argued a case before the Supreme Court in which the Rotary Club of Duarte, California, had been expelled from the National Rotary Club for admitting women. Resnik convinced the Supreme Court that because the National Rotary Club is a business organization, the expulsion violated the Civil Rights Act and must be reversed. Within a week, I was given her number to call. She later told me that she rarely agreed to help in such cases, but the law professor who had shown her the material was normally so conservative that she believed the denial of tenure must be egregious. Resnik is a font of energy and her energy revived me. We talked extensively on the phone. When she learned the low percentage of women on the Caltech faculty, she was shocked and became more committed to helping. She was not in a position to act as my “lawyer of record,” so she ultimately found a former student who worked in a Westwood law firm to act as my formal legal representative to Caltech, but Resnik continued to advise me.

Barclay Kamb had been newly appointed Caltech provost at the beginning of 1987. This was fortunate for me because he had been one of the few division chairs who had initially argued in favor of promoting Jenijoy LaBelle to tenure. Through the summer, Eleanor Searle became a messenger between Kamb and me. I soon learned that he was not pleased with the report of the AFTC for the same reasons that Eleanor had found it laughable. Eleanor told him that she wanted to be loyal to Caltech, but she needed to inform him that I had the help of a very talented lawyer at USC (Resnik) who had argued before the Supreme Court. I learned that institute administrators regarded it as disloyal to consider legal action against the institute. Many administrators felt that it was appropriate to tell faculty or employees that they should not consult outside lawyers. I believe that if we are a country of laws, the institute should accept that sometimes employees will need their own lawyers and may need to bring litigation in a dispute. However, Eleanor wanted to be able to act as a messenger between the provost and me, without being seen as an adversary. I greatly admired her diplomatic skill in helping Provost Kamb work through the difficult situation he found himself in.

Kamb told Eleanor that I should have the lawyer contact him. So I went to see the “lawyer of record” from the Westwood law firm that Resnik had obtained for me. This lawyer then wrote a polite letter to the provost introducing herself, saying that her firm was representing me, and listing all the federal and state laws that they believed Caltech had violated. Kamb interviewed a few possible defense attorneys who told him not to let the case get to court. Throughout this time, he also met with me more than once, and he asked that I not take action without letting him know first. I agreed to that, and explained to him that I was in constant contact with Resnik, as well as the lawyer from the Westwood firm.

During this period, Kamb began receiving unsolicited additional letters from neurobiologists supporting my promotion to tenure. Zach Hall, who was then chair of the Physiology Department at the University of California–San Francisco, had suggested this action and volunteered to organize it.

At one point in this interval, Eleanor called me to say that someone had suggested to Kamb that Caltech offer me $25,000 to drop the issue. I was stunned by this news because such a thing had never occurred to me. I blurted out, “I don’t want their goddamn money.” Eleanor replied, “Oh, I’m so glad you said that.” I never heard another word about it.

As he planned his strategy, Kamb enlisted the help of Trustee Shirley Hufstedler, a distinguished jurist who had sat on the Ninth Circuit Court of Appeals. I knew that I had won when Kamb called me at 9:00 p.m. one night to tell me that he had spent the day talking with Hufstedler and she saw the case my way. As in the LaBelle case, my tenure case on paper was much stronger than that of the previous male who had been awarded tenure in the division. There was one hitch. Resnik had let me know that the statute of limitations for filing a “charge of discrimination” with the Equal Employment Opportunity Commission (EEOC) was the next day. I had let Kamb know this, which was why he called me late at night. I was preparing to drive down to the EEOC office in Los Angeles the next day to file a complaint. But Kamb told me that Hufstedler had asked me to please not file because it would be easier for her to convince the trustees if I was not in “an adversarial position” with Caltech. I told Kamb that I would have to talk to Resnik and called her immediately. I clearly remember her saying, “Oh, that Shirley! You have to file. You can’t pass the statute of limitations without losing your legal options.” We finally came to the decision that if Kamb would write a letter to me “stipulating” that the “act of discrimination” had not occurred on the day that the faculty voted, but rather six weeks later when the Academic Council voted, we would not need to file the complaint right away. Kamb immediately agreed and early the next day, he walked over to my office and gave me the required letter.

With Hufstedler’s help, Kamb convinced the rest of the administration and the trustees that I should be promoted to tenure. Apparently, he asked Hufstedler to explain this to Lee Hood. Finally, on July 30, I watched Kamb walk over to my office from the administration building carrying a brown paper bag and a letter. The letter notified me of my promotion to tenure and the bag contained a bottle of champagne that he presented to me.

In a small way, this episode illustrates once again how important it is who holds power in our institutions. For the rule of law to survive, it isn’t enough to have laws on the books. They must be enforced. The only means of enforcement is through the individuals in positions of power throughout our institutions.

The neuroscientists and many friends who had given me help and support celebrated with me. Without my friend Susan Goelz who had moved with her husband to Caltech to do postdoctoral work, Eleanor Searle, Jenijoy LaBelle, many women of the Organization for Women at Caltech, Robert Nelson, Peggy Renner, John McTernan, Zach Hall, Barclay Kamb, Shirley Hufstedler, and my sisters and brother in the Seattle area, I wouldn’t have survived this period. The difficult year also took a toll on my students who were bewildered by the turmoil they witnessed. They couldn’t help but feel that it had something to do with their work; I tried to assure them that it didn’t. All of them accepted excellent postdoctoral fellowships; Mark Bennett, Ngozi Erondu, and Stephen Miller went on to hold senior positions at pharmaceutical companies.

Epilogue

Having finally secured full independence, and a new NIH grant, I was able to steer my lab toward a project I had always wanted to take on; the molecular identification of the proteins that make up the postsynaptic density. Ironically, we began to use techniques that Hood and his collaborators had advocated, gas phase sequencing of proteins in gel bands, followed by cDNA cloning, to fully identify the more abundant proteins in Siekevitz’s PSD fraction. This approach led to the identification of PSD-95, for which my lab is best known, as well as synGAP, densin, and subunits of the NMDA receptor. Other labs began adding to the list, and we now know the identities of essentially all of the major PSD protein scaffolds and enzymes. With Peter Seeburg’s lab, we discovered that PDZ domains in PSD-95 mediate interaction with specific ligands at the carboxyl tail of NMDA receptors. PDZ domains also underlie many other protein interactions in the PSD and control immobilization of NMDA- and AMPA-type glutamate receptors at the postsynapse. The task now is to understand how the protein lattice is assembled and how the PSD is reshaped during increases and decreases in synaptic strength (i.e., LTP and long-term depression [LTD]). As I had always known, changes in synaptic function, driven by structural processes, including modulation of PSD structure, spine shape and size, and the number of glutamate receptors at each synapse, are determined by interconnected regulatory networks, much like those of metabolism itself. New concepts such as liquid-liquid phase separation of protein mixtures are providing new ways of approaching these questions. NIH has recently shifted neuroscience funding away from biochemistry and cell biology toward circuit tracing. If NIH should choose again to adequately fund the biochemical study of neurons and synapses, U.S. universities can still lead in this critically important area.

The environment for women at Caltech has now changed dramatically for the better. After 1987, I and my female, and some male, colleagues worked hard to push back on sexist attitudes and make changes to improve the work and study environment for women. Caltech began to work even harder at hiring female faculty and gradually most of the divisions have reached at least a critical mass of women, and about half of the undergraduate student body is female. It is still difficult for assertive women to gain influence in the administration. Many male scientists still have difficulty recognizing a woman as an independent authority. The more congenial women are usually chosen for administrative positions. However, I have observed that this has also meant that overly aggressive men have less influence than they used to, and obvious sexist attitudes are not rewarded. One of the most insidious social influences that has held women back is reflexive negative feedback (both subtle and blatant) for positive achievements when they do not conform to a female stereotype. I believe that my resistance to the negative feedback for my positive achievements by Lee Hood and his colleagues, and the courageous help that I received from many others on the Caltech faculty helped to shock the Caltech culture into recognizing that hiring more women and treating them appropriately is necessary for a modern scientific institution to survive.

Selected Publications

Kennedy, M.B. and Greengard, P. Two calcium/calmodulin-dependent protein kinases, which are highly concentrated in brain, phosphorylate protein I at distinct sites. Proc. Natl. Acad. Sci. USA 78: 1293–1297, 1981.

Kennedy, M.B., McGuinness, T., and Greengard, P. Partial purification, characterization and comparison of soluble and particulate calmodulin-dependent synapsin I kinase activities. J. Neurosci. 3: 818–831, 1983.

Kennedy, M.B. Experimental approaches to understanding the role of protein phosphorylation in the regulation of neuronal function. Ann. Rev. Neurosci. 6: 493–525, 1983.

Bennett, M.K., Erondu, N.E., and Kennedy, M.B. Purification and characterization of a calmodulin-dependent protein kinase that is highly concentrated in brain. J. Biol. Chem. 258: 12735–12744, 1983.

Kennedy, M.B., Bennett, M.K., and Erondu, N.E. Biochemical and immunochemical evidence that the “major postsynaptic density protein” is a subunit of a calmodulin-dependent protein kinase. Proc. Natl. Acad. Sci. USA 80: 7357–7361, 1983.

Miller, S.G. and Kennedy, M.B. Distinct forebrain and cerebellar isozymes of Type II Ca²⁺/calmodulin-dependent protein kinase associate differently with the postsynaptic density fraction. J. Biol. Chem. 260: 9039–9046, 1985.

Erondu, N.E. and Kennedy, M.B. Regional distribution of Type II Ca²⁺/calmodulin-dependent protein kinase in rat brain. J. Neurosci. 5: 3270–3277, 1985.

Miller, S.G. and Kennedy, M.B. Regulation of brain type II Ca²⁺/calmodulin-dependent protein kinase by autophosphorylation. A Ca²⁺-triggered molecular switch. Cell 44: 861–870, 1986.

Bennett, M.K. and Kennedy, M.B. Primary structure of the ß-subunit of brain type II Ca²⁺/calmodulin-dependent protein kinase deduced by molecular cloning. Proc. Natl. Acad. Sci. USA 84: 1794–1798, 1987.

Miller, S.G., Patton, B.L., and Kennedy, M.B. Sequences of autophosphorylation sites in neuronal type II CaM kinase that control Ca²⁺-independent activity. Neuron 1, 593–604, 1988.

Kennedy, M.B. Regulation of synaptic transmission in the central nervous system: long term potentiation. Cell, 59, 777–787, 1989.

Patton, B.L., Miller, S.G., and Kennedy, M.B. Activation of type II CaM kinase by Ca²⁺/calmodulin is inhibited by autophosphorylation of threonine within the calmodulin binding domain. J. Biol. Chem. 265, 11204–11212, 1990.

Kennedy, M.B., Bennett, M.K., Bulleit, R.F., Erondu, N.E., Jennings, V.R., Miller, S.G., Molloy, S.S., Patton, B.L, and Schenker, L.J. Structure and regulation of type II Ca²⁺/calmodulin-dependent protein kinase in central nervous system neurons. C.S.H. Symp. Quant. Biol. 55, 101–110, 1990.

Cho, K.-O., Hunt, C.A., and Kennedy, M.B. The rat brain postsynaptic density fraction contains a homologue of the Drosophila discs-large tumor suppressor protein. Neuron 9, 929–942, 1992.

Patton, B.L., Molloy, S.M., and Kennedy, M.B. Autophosphorylation of type II CaM kinase in hippocampal neurons: Localization of phospho- and dephosphokinase with complementary phosphorylation site-specific antibodies. Molec. Biol. Cell 4, 159–172, 1993.

Kennedy, M.B. The biochemistry of synaptic regulation in the central nervous system. Annu. Rev. Biochem. 63, 571–600, 1994.

Moon, I.-S., Apperson, M.L., and Kennedy, M.B. The major tyrosine-phosphorylated protein in the postsynaptic density fraction is N-methyl-D-aspartate receptor subunit 2B. Proc. Natl. Acad. Sci. USA 91, 3954–3958, 1994.

Kornau, H.-C., Schenker, L.T., Kennedy, M.B., and Seeburg, P.H. Domain interaction between NMDA receptor subunits and the postsynaptic density protein PSD-95. Science 269, 1737–1740, 1995.

Omkumar, R.V., Kiely, M.J., Rosenstein, A.J., Min, K.-T., and Kennedy, M.B. Identification of a phosphorylation site for calcium/calmodulin-dependent protein kinase II in the NR2B subunit of the N-methyl-D-aspartate receptor. J. Biol. Chem. 271, 31670–31678, 1996.

Apperson, M.L., Moon, I.-S., and Kennedy, M.B. Characterization of Densin-180, a new brain-specific synaptic protein of the O-sialoglycoprotein family. J. Neurosci. 16, 6839–6852, 1996.

Kennedy, M.B. The postsynaptic density at glutamatergic synapses. Trends Neurosci. 20, 264–268, 1997.

Chen, H.-J., Rojas-Soto, M., Oguni, A., and Kennedy, M.B. A synaptic Ras GTPase-activating protein (p135 SynGAP) inhibited by CaM kinase II. Neuron 20, 895–904, 1998.

Ouyang, Y., Rosenstein, A., Kreiman, G., Schuman, E. M., and Kennedy, M.B. Tetanic stimulation leads to increased accumulation of Ca²⁺/ calmodulin-dependent protein kinase II via dendritic protein synthesis in hippocampal neurons. J. Neurosci. 19, 7823–7833, 1999.

Walikonis, R.S., Jensen, O.N., Mann, M., Provance, D.W. Jr., Mercer, J.A., and Kennedy, M.B. Identification of proteins in the postsynaptic density fraction by mass spectrometry. J. Neurosci. 20, 4069–4080, 2000.

Kennedy, M.B. Signal processing machines at the postsynaptic density. Science 290, 750–754, 2000.

Walikonis, R. S., Oguni, A., Khorosheva, E. M., Jeng, C.-J., Asuncion, F. J., and Kennedy, M.B. Densin-180 forms a ternary complex with the a-subunit of CaMKII and a-actinin. J. Neurosci. 21, 423–433, 2001.

Oh, J. S., Manzerra, P., and Kennedy, M.B. Regulation of the neuron-specific Ras GTPase activating protein, synGAP, by Ca²⁺/ calmodulin-dependent protein kinase II. J. Biol. Chem. 279, 17980–17988, 2004.

Vazquez, L.E., Chen, H.-J., Sokolova, I., Knuesel, I., and Kennedy, M.B. SynGAP regulates spine formation. J. Neurosci. 24, 8796–8805, 2004.

Carlisle, H.J. and Kennedy, M.B. Spine architecture and synaptic plasticity. Trends Neurosci. 28, 182–187, 2005.

Kennedy, M.B., Beale, H.C., Carlisle, H.J., and Washburn, L.R. Integration of biochemical signalling in spines. Nat. Rev. Neurosci. 6, 423–434, 2005.

Shifman, J. M., Choi, M.H., Mihalas, S., Mayo, S.L., and Kennedy, M.B. Ca²⁺/calmodulin-dependent protein kinase II is activated by calmodulin with two bound calciums. Proc. Natl. Acad. Sci. USA 103, 13968–13973, 2006.

Lûcic, V., Greif, G.J., and Kennedy, M.B. Detailed state model of CaMKII activation and autophosphorylation. Eur. Biophys. J. 38, 83–98, 2008.

Carlisle, H.J., Manzerra, P., Marcora, E., and Kennedy, M.B. SynGAP regulates steady-state and activity-dependent phosphorylation of cofilin. J. Neurosci. 28, 13649–13683, 2008.

Pepke, S., Kinzer-Ursem, T., Mihalas, S., and Kennedy, M.B. A dynamic model of interactions of Ca²⁺, calmodulin, and catalytic subunits of Ca²⁺/calmodulin-dependent protein kinase II. PLoS Comput. Biol. e1000675, 2010.

Marcora, E. and Kennedy, M.B. The Huntington’s disease mutation impairs Huntingtin’s role in the transport of NF-kB from the synapse to the nucleus. Human Mol. Gen. 19, 4373–4384, 2010.

Carlisle, H.J., Luong, T.N., Medina-Marino, A., Schenker, L.T., Khorosheva, E.M., Indersmitten, T., Gunapala, K.M., Steele, A.D., O’Dell T. J., Patterson, P.H., and Kennedy, M.B. Deletion of densin-180 results in abnormal behaviors associated with mental illness and reduces mGluR5 and DISC1 in the postsynaptic density fraction. J Neurosci. 31, 16194–16207, 2011.

Kennedy, M.B. Synaptic signaling in learning and memory. CSH Perspect. Biol., a016824, 2013.

Stefan, M.I., Bartol, T.M., Sejnowski, T.J., and Kennedy, M.B. Multi-state modeling of biomolecules. PLoS Comput. Biol. 10, e1003844, 2014.

Walkup, W.G.t., Washburn, L., Sweredoski, M.J., Carlisle, H.J., Graham, R.L., Hess, S., and Kennedy, M.B. Phosphorylation of synaptic GTPase-activating protein (synGAP) by Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and cyclin-dependent kinase 5 (CDK5) alters the ratio of its GAP activity toward Ras and Rap GTPases. J. Biol. Chem. 290, 4908–4927, 2015.

Bartol, T. M., Keller, D.X., Kinney, J.P., Bajaj, C., Harris, K.M., Sejnowski, T.J., and Kennedy, M.B. Computational reconstitution of spine calcium transients from individual proteins. Front. Synapt. Neurosci. 7:17. doi: 10.3389/fnsyn.2015.00017, 2015.

Walkup, W.G.t., Mastro, T.L., Schenker, L.T., Vielmetter, J., Hu, R., Iancu, A., Reghunathan, M., Bannon, B.D., and Kennedy, M.B. A model for regulation by synGAP-α1 of binding of synaptic proteins to PDZ-domain ‘slots’ in the postsynaptic density. eLife 5, e16813, 2016.

Mastro, T.L., Preza, A., Basu, S., Chattarji, S., Till, S.M., Kind, P., and Kennedy, M.B. A sex difference in the response of the rodent postsynaptic density to synGAP haploinsufficiency. eLife 9, e52656, 2020.

Eric I. Knudsen

BORN:

October 7, 1949

Palo Alto, California

EDUCATION:

University of California, Santa Barbara, BA (1971)

University of California, Santa Barbara, MA (1972)

University of California, San Diego, PhD (1976)

APPOINTMENTS:

Assistant Professor, Department of Neurobiology, Stanford

University School of Medicine (1979–1985)

Associate Professor, Department of Neurobiology, Stanford

University School of Medicine (1985–1988)

Professor, Department of Neurobiology, Stanford

University School of Medicine (1988–2016)

Edward C. and Amy H. Sewall Professor, Stanford University School of Medicine (1995–2016)

Chair of Neurobiology, Stanford University School of Medicine (2001–2006)

Professor Emeritus, Department of Neurobiology, Stanford

University School of Medicine (2016–present)

HONORS AND AWARDS (SELECTED)

Newcomb Cleveland Prize, American Association for the Advancement of Science (1978)

Young Investigator Award, Society for Neuroscience (1984)

Troland Research Award, National Academy of Sciences (1988)

American Academy of Arts and Sciences, Fellow (1996)

National Academy of Sciences, Member (2002)

Gruber Prize in Neuroscience, Society for Neuroscience (2005)

Karl Spencer Lashley Award, American Philosophical Society (2008)

American Philosophical Society, Member (2016)

Eric Knudsen has devoted his career to studying how the brain processes information, learns from experience, and selects information for attention. His early research mapped out neural pathways in birds that process auditory spatial information and mediate orienting behavior. A major advance was his discovery with Mark Konishi at Caltech of a topographic map of auditory space in the midbrain of barn owls, a map that results from sophisticated neural computations. Then, with colleagues at Stanford University, he demonstrated how experience during early life shapes the circuits that create this computational map, identified specific sites of adaptive plasticity as well as rules and mechanisms of learning, and discovered methods for increasing plasticity in adult animals. Later, his research shifted to mechanisms that control selective attention. With colleagues at Stanford, he developed behavioral paradigms that quantify the effects of spatial attention in birds and established methods to manipulate signals in the forebrain that modulate sensory information in an attention-like manner. Combining computational approaches with brain slice technologies, he demonstrated how specific brain circuits select information for cognitive decisions, and how other circuits suppress distracting information.

Eric I. Knudsen

Prologue

I have spent my scientific career exploring the mechanisms by which the brain mediates behavior. My love for science began at an early age, and doing science has always been pure pleasure. Throughout my career, I have enjoyed complete freedom to follow my research interests wherever they might lead, and I continue to be amazed that I actually get paid to follow my passion: studying the brain. My interest in the brain applies to the brains of all animals, not just to those of humans. I have found the evolution of the brain to be fascinating as well as uniquely instructive, and I have repeatedly exploited the diversity of species as a tool for discovery.

Over the course of my professional life, my research interests have transitioned from how the brain organizes and processes information, to how it learns from experience, and finally to how it selects information in real-time for attention and decision making. These transitions were stimulating and rejuvenating, as each transition expanded my knowledge in new directions and introduced me to new bodies of literature and communities of scientists. Exploring each of these different aspects of brain function has given me a broad perspective of brain structure, function, and development.

My achievements are a testament to the importance of motivation, focus, and persistence to success in science. In meetings, I am rarely the smartest person in the room. However, I am extremely focused and compulsively organized, and once I have settled on a goal, I am like a bulldog in pursuing it. In this pursuit, I have learned to pay particular attention to findings that deviate from my expectations. Typically, these deviations have arisen from errors in experimental design or data analysis, but sometimes not, and when not, they have led to important advances, if not breakthroughs, in my understanding of a subject. Also, I have learned that nature’s solutions to biological problems are almost always simple and logical. When a solution seemed complicated, it was because I did not understand the problem in sufficient detail. When analyzed with sufficient resolution, nature’s solutions became intuitively obvious and elegantly simple.

Along with the pursuit of science, working with colleagues and students has been the most inspiring and fulfilling aspect of my professional career. By nature, I am introverted and uncomfortable with public speaking (although I love to talk science in private with anyone!). Early on, I thrived on working alone, and my first 10 publications were single-author publications. Fortunately, I learned as a postdoc the joys and benefits of collaborative research and, as an assistant professor, the rewards of teaching. These social interactions greatly enriched my life. I have had the privilege of working with brilliant colleagues and teaching some of the brightest and most talented students in the world. These interactions made the scientific quest a fun adventure, and most of what I have achieved scientifically resulted directly from these interactions.

Early Years

I was born in Palo Alto, California, in a hospital just a short walk from my laboratory at Stanford Medical School where I spent nearly my entire career as a neuroscientist. I was a baby boomer, born in 1949 to second-generation Norwegian parents. My father was a New Yorker and had just finished fighting in the Pacific theater in World War II. My mother, also from New York, had interrupted her studies at University of California Los Angeles to marry my father when he returned home from the war. When I was born, they were raising my two-year-old sister, Linda, in a rustic cabin with no running water, in the Santa Cruz Mountains behind Palo Alto, while my father attended the Stanford School of Business. Six years later, we were joined by my second sister, Anne, and after another nine years, by my brother, Karl.

I was raised in the Palo Alto area, except for a few years (ages 9–12) when my family lived in Seal Beach in southern California. Those early years of living at the beach had a major impact on my life. I found that I loved being in and on the ocean, probably an expression of the seafaring genes of my Norwegian ancestors. I spent these formative years walking the sand, fishing, sailing, and body surfing. I was also an avid collector: seashells, rocks, butterflies, whatever. Each collection was organized and the items labeled. Later on, this passion would be expressed as a passion for collecting and organizing scientific data.

When I was 12, my family moved back to Palo Alto, where I completed my high school education. My love of the outdoors and fascination with nature grew. During junior high school, I was heavily involved in the Boy Scouts; both my father and mother were scout leaders, and I became an Eagle Scout. My parents loved the mountains. Family traditions included skiing in the winter and hiking and camping in the summer. I attended summer camps that featured hiking, fishing, and animal husbandry. Meanwhile, my collections continued to grow.

At the beginning of high school, my father quit his job as an office manager and started his own printing business, a profession he had learned from his father. To purchase equipment and rent space for his print shop, we sold our home and rented an old ranch house in the hills behind Palo Alto. The ranch included a barn, pastures, and large apricot and plum orchards. To help cover family expenses, we boarded horses. We also kept chickens and cats (both of which became important later in my scientific studies), goats, and dogs. I fed the animals, rode the horses, and went everywhere with my dog. As a result of extensive, daily interactions with these various kinds of animals, I learned to appreciate their sophisticated behaviors, as well as their abilities to communicate with each other and with me. I spent countless hours watching and training these animals.

In high school I realized my interest in the natural sciences. In particular, ecology and biology fascinated me. I was mildly dyslexic, and in elementary school, I had received special training in a failed attempt to improve my spelling and reading abilities. Ironically, in high school I found that I enjoyed writing, which proved to be extremely valuable in my research career. I was good at subjects that did not require lots of reading, were logical, and in which the material could be visualized: for example, geometry and physics. I was poor at subjects that required memorization of arbitrary facts or words; I never did learn Spanish despite two tedious years of trying.

While my interests in academics were developing, I also became interested in cars and organized sports. I worked regularly on an old car that I used to drive to school each day. I played water polo and soccer for my high school teams. I also became a scuba diver and an avid surfer, both direct results of my earlier life at Seal Beach. Toward the end of my high school years, surfing became an obsession, and I would drive my old car over the Santa Cruz Mountains to the beach almost every weekend.

To make money, I worked for my father in his print shop. Also, in the middle of summer, I returned to Seal Beach to work as a deckhand on a tuna fishing boat. The boat stayed out for many days at a time, as we followed the schools of Albacore migrating up the southern coast of California.

In 1967, I left home for my undergraduate education at University of California Santa Barbara (UCSB). I chose zoology as my major, and I immersed myself in academics. This was balanced with daily surfing and playing soccer with the university team. During my junior year, I went to study in Goettingen, Germany, as part of the education abroad program. There, I learned to speak German, traveled extensively throughout Europe, and experienced a variety of foreign cultures. This experience dramatically expanded my worldview. My social skills matured, and I became confident.

Awakening to Neuroscience

As a senior at UCSB finishing my undergraduate degree in zoology, I carried out a research project on the daily movement and feeding patterns of limpets in the intertidal zone. I was captivated by this biological research, and I realized that I wanted to become a marine scientist. I also realized that I had no clue how to pursue this goal. So, I went to talk with my academic advisor, Dr. James (“Jim”) Case, who was a neuroscientist. Jim encouraged my desire to become a scientist, but he recommended that I try more controlled, laboratory research before committing to marine ecology.

Jim’s main focus of research was bioluminescent communication in invertebrates. Along with other exotic marine invertebrates in his laboratory, Jim had an aquarium containing the bioluminescent sea pansy (Renilla), a colonial cnidarian that lives in the sand on the ocean floor. He suggested that I study the properties of this animal’s bioluminescent signaling. I was immediately struck by the beauty of its behavior: in response to gentle tactile stimulation, Renilla produces a wave of brilliant, blue-green light that sweeps across its leaf-shaped surface. The light is triggered by signals traveling in the animal’s nervous system, so the bioluminescence displays the properties of neural signaling (all-or-none activation threshold, propagation, refractory period). The traveling waves of light exhibit the same properties as do electrical waves in the developing retina of vertebrates, but the waves can be seen with the naked eye! I spent the spring of my senior year in Jim’s lab characterizing how incident light interferes with this bioluminescence.

Because of the enthusiasm with which I tackled this project, Jim invited me to stay on in his lab as a master’s student and to join him for a summer of research at the Marine Biological Laboratory at Woods Hole. This was in 1971. It was the exposure to neuroscience at Woods Hole that set me firmly on a path to becoming a neuroscientist. I took the invertebrate zoology course taught by Jim and Alan Gelperin, a professor from Princeton. The course included an independent project. Mine was studying the neural signals that control the rhythmic ventilation (breathing) and swimming movements of horseshoe crabs, which litter the beaches around Woods Hole. This was my first experience with recording neural signals in animals that were involved in generating movements. I watched with rapt fascination as the rhythmic signals recorded from motor neurons, transitioned from patterns for ventilation to swimming and back to ventilation. By listening to these neural signals played through an audiomonitor, I could predict exactly what the animal was about to do! I was hooked.

My research revealed that the neural circuits that generated the rhythmic, oscillatory patterns for ventilation and swimming were located in each of the crab’s abdominal ganglia (Knudsen, 1973). This was my first experience with scientific discovery, and I was instantly addicted. For me, nothing compares with the thrill that comes with discovery. These “aha” moments have been unforgettable in my career and have stoked my passion for research.

For my master’s thesis, I expanded on this summer project with additional experiments in Jim’s lab at UCSB, including cell-tracing studies (neuronal labeling techniques were just being invented) and kinematic measurements. I found that interganglionic connections regulated the strength and timing of the outputs of the ganglionic pattern generators, thereby coordinating the movements of all the crab’s appendages (Knudsen, 1975a).

At this time, the field of neuroscience was still in its “wild west” stage. Our understanding of the nervous system was primitive, and the basic tools for conducting research were just being developed (computers had not yet entered the laboratory, and the ability to fabricate various kinds of microelectrodes was an essential skill). Jim supported me, even though my research topic was far outside of his field of interest. Research was driven solely by curiosity, and there was no particular emphasis on studying the human brain or its diseases. Lab members were free to choose their questions, as well as the best species and techniques to answer those questions. This complete freedom to follow my own interests and instincts was exhilarating. I had found my career path.

Graduate Studies with Ted Bullock

While I was completing my master’s degree at UCSB, down the California coast at University of California San Diego (UCSD), a Department of Neuroscience had been created through the recent hiring of several international leaders in neuroscience. Dr. Theodore (“Ted”) Bullock was one of these leaders. Ted had received worldwide acclaim for his encyclopedic tome (written with Adrian Horridge) that reviewed everything that was known about the nervous systems of invertebrates (Structure and Function in the Nervous System of Invertebrates). Jim admired Ted’s work, and he recommended that I go to UCSD to pursue my research interests with Ted.

I was accepted into the UCSD Neuroscience Graduate Program in the fall of 1972. I loaded up my red VW bug with my few possessions and drove down to La Jolla (the town where UCSD is located). I had arranged to meet with Ted on that same day, in his office at the Scripps Institution of Oceanography. The walls of his office were lined with aquaria containing all kinds of exotic fish, particularly electric fish (including one huge electric eel). I told Ted about my research at UCSB and showed him a video of the bioluminescent waves of Renilla. He became quite excited and animated as we discussed the nervous system and ecology of Cnidarians. Ted invited me to join his lab, and when I returned a few days later, he had already placed my name on the door to one of his student lab rooms. I was in heaven: welcomed into the lab of a brilliant neuroscientist, with my own lab room, located just a short walk from above-average surf.

Although Ted did research on every aspect of brain function (from why sloths are slow, to bat sonar, to the properties of slow wave field potentials in marine rays), when I joined his lab, most of the research projects centered on the recently discovered, electric sense in weakly electric fish (fish that possess electric organs). Because of my early experience with training farm animals, I chose as my first project to train different species of electric fish to report behaviorally when they detected electric fields of different frequencies and strengths (Knudsen, 1974). I also measured the strength of the electric fields that different species emitted from their electric organs (Knudsen, 1975b). When combined, these measurements enabled me to estimate distances for the electro-detection of objects and for electro-communication among conspecific fish.

I was independent and headstrong, and I valued the feeling of striking out in my own new direction. So, after a year of working with electric fish, I turned my attention to the less-studied, low-frequency electric sense that is possessed by a much wider range of marine species. This sense depends on a special class of electroreceptors that detects standing (direct current) electric fields and is used by fish, sharks, rays, and a few other aquatic vertebrates to locate prey and to navigate in the earth’s magnetic field.

For my doctoral thesis, I studied the characteristics of low-frequency electric fields that are analyzed in the catfish midbrain and how the information is represented. Among other things, I found that input from different sensory organs (which together form the acoustico-lateralis system of fishes) is processed in different anatomical subdivisions of the midbrain nucleus (Knudsen, 1978). I also found that the lateral subdivision of this nucleus contains a topographic map of space around the fish (Knudsen, 1976), a finding that was to play a crucial role in my hunt, as a postdoc, for an auditory map of space in owls.

Like Jim at UCSB, Ted gave the people in his lab complete freedom to choose their research projects and experimental species. When it came time to publish, Ted (like Jim) signed on as an author only when he had participated directly in the research (a practice that has been lost in contemporary science). As a result, throughout my years as a graduate student, all of my publications were single-author publications. In hindsight, it would have been good for the historical record to have Jim’s and Ted’s names on at least some of those papers.

During this period, I met and married my wife, Phyllis, who at the time was working toward a master’s degree in fisheries biology. She was to become my lifelong research collaborator and laboratory manager.

Ted’s mentoring established the foundation for my career in neuroscience. He created an extraordinarily rich atmosphere of scholarship and research. He attracted to his lab a large number of exceptionally talented postdocs and visiting professors, mostly from foreign countries. His international reputation also brought traveling scholars to visit the lab. He would host special lab meetings, in addition to our weekly meetings, and give everyone a chance to interact with these scholars. Ted had an eidetic memory, was extremely knowledgeable about all aspects of neuroscience, and enjoyed engaging in spirited, scientific debates. Always the gentleman, he would tailor his discussions to match the interests and sophistication of his company, guiding the discussions and making everyone feel involved. Listening to experts engage in debates about current issues in neuroscience was an effective and entertaining way to learn about science, people, and how to communicate ideas.

Postdoctoral Studies with Mark Konishi

While studying the catfish midbrain, I had observed that the processing of different kinds of information took place in different subdivisions within a structure. I became interested in whether the same principle applies to the central auditory system of terrestrial vertebrates as well. Specifically, my question was: given that the auditory system analyzes sound location and sound identity using fundamentally different kinds of computations, are these respective computations carried out by anatomically segregated, functionally specialized groups of neurons?

A visiting foreign scholar in Ted’s lab, Walter Heiligenberg, was a close friend of Masakazu (“Mark”) Konishi. Mark had just published spectacular behavioral studies demonstrating the remarkable sound localization capabilities of barn owls. Knowing my interests in studying the processing of stimulus location versus identity in the auditory system, Walter had recommended that I contact Mark about a postdoctoral position in his lab. Fortunately for me, Mark had just moved from Princeton to the California Institute of Technology (Caltech), just up the road from UCSD.

Mark and I met to discuss his research plans at the 1975 Society for Neuroscience meeting (Ted had just finished serving as president of this new society). Mark described to me his intuition that the extreme dependence of barn owls on accurate sound localization for hunting at night would be reflected in an exceptionally high degree of differentiation in their nervous systems for processing auditory spatial information. His plan was to study auditory spatial processing by recording from neurons in the owl’s central auditory pathway while presenting sounds from various locations in anechoic space. This approach was relatively novel because the prevailing method for studying auditory space processing was to deliver sounds through earphones and to simulate spatial cues. To enable Mark to pursue a more natural, “free-field” approach, Caltech had built Mark a large (3 × 3 × 5 m) anechoic room, and a gifted Caltech machinist (who also built Mars landers for NASA) had constructed a speaker-moving system that could position a small speaker at any precisely controlled location, by remote control, on a 1-m-radius sphere centered on the owl’s head. With this equipment, we could test the effects of sound source location independently of all other sound properties.

Mark and I were both excited by our discussions at the Society for Neuroscience meeting, and within a few days of returning from the meeting, I had agreed to join his lab as a postdoc to study the processing of auditory spatial information in barn owls. So, after finishing my doctorate with Ted, Phyllis and I packed up my VW bug and drove to Caltech to begin this new line of research.

To develop protocols for recording from the owl’s brain, Mark had teamed-up with John (“Jack”) Pettigrew, a faculty colleague who was an expert in cat visual neurophysiology. Before I arrived, Mark and Jack had completed several pioneering studies on information processing in the owl’s central visual system and the influence of early visual experience on the development of that system.

The first issue that Mark and I discussed after I arrived was to answer the question: Given the myriad computations that are carried out by the auditory system to analyze sounds, what is the most efficient strategy to identify those computations that are specifically relevant to analyzing stimulus location? We decided to take a “top-down” approach: The idea was to begin by studying how the brain represents space at the highest levels in the auditory pathway. Then, once we understood these high-level representations, we would study specifically how lower-level brain areas process the information used for computing the high-level representation.

We began our top-down attack in the owl’s forebrain auditory area called Field L, equivalent to the auditory cortex in mammals. We presented sounds in the free field (rather than through earphones), allowing the owl’s external ears to filter sounds naturally, thereby providing all possible spatial cues to the auditory system (the auditory system derives spatial information from frequency-specific differences in the timing and level of sound at the two ears and from the sound’s amplitude spectrum, which is shaped by the physical acoustic effects of the head and external ears).

We surveyed the responses of Field L neurons and occasionally encountered neurons that excited us: they could be driven only by sounds originating from a small region of space (receptive field, RF). When we found such a neuron, we spent hours presenting sounds of different kinds (machine-made tones, clicks and noise bursts, and manmade sounds, including rubbing sandpaper, crinkling foil, or snapping fingers) from various locations. Some “space-tuned” forebrain neurons could be driven only by one type of sound, whereas others responded to wide ranges of sound types. Crucially, however, the locations of their RFs remained constant, independent of sound type or level (Knudsen et al., 1977).

Unfortunately, the vast majority of Field L neurons were not of this kind. Typical neurons responded with broad or complex spatial tuning that changed with the spectral properties of the sound. After several months of studying Field L neurons, we became convinced that space analysis was not a primary function of this forebrain auditory area.

In my doctoral research on the acoustico-lateralis system of catfish, I had found that a particular portion of a midbrain nucleus contained a topographic map of the fish’s body surface; a map of space (Knudsen, 1978). The equivalent nucleus in the auditory system of mammals is called the inferior colliucus (IC). Before moving to another forebrain auditory area in the owl, we decided that we should try recording from the IC in the owl’s midbrain. I adjusted the trajectory of the electrode to target this structure. On the first attempt, the electrode entered the external nucleus of the inferior colliculus (ICX) and recorded a unit that exhibited the sharpest auditory RF that I had ever seen. This was an unforgettable moment. I ran to get Mark to show him this amazing unit before it was lost. Having spent so long studying neural responses in Field L, it was immediately apparent to both of us that this unit was special: its responses were highly space-specific and it was not selective for sound type or level.

We repeated this experiment numerous times and found that nearly all ICX units were of this special, space-specific type. Following this discovery, additional discoveries came in rapid succession. Most important, we noticed that neighboring ICX units were tuned for nearly the same location and that the locations of the RFs were different in different experiments. Therefore, we prepared for a marathon experiment, in which we would measure RF locations from as many electrode penetrations as possible. The experiment lasted all night and into the next day. In the course of the experiment, it became apparent that RF locations moved systematically from high to low along single electrode penetrations, and from frontal to peripheral as we moved the electrode caudally in the ICX (Knudsen and Konishi, 1978b). Clearly, the ICX represented auditory space as a topographic map. This was another unforgettable moment of discovery. For the final electrode penetration, beginning at about 6 a.m. on the second day, we accurately predicted the RF locations for all three sequential recording sites. We celebrated this moment with bleary-eyed gusto over a late breakfast.

The discovery of an auditory space map was significant because it was a clear demonstration that the brain can create a topographic representation of information that it derives solely through computations (i.e., a computational map). The auditory space map is based on the brain’s evaluation and interpretation of interaural time differences (ITD), interaural level differences (ILD), and amplitude spectra. The map demonstrated that the brain arranges neurons topographically within the ICX so that the tuning of neurons to values of ITD, ILD and amplitude spectrum matches the pattern of these cue values as they vary across space for the owl. This discovery led to my first award for science: the Newcomb Cleveland Prize (for “best paper of the year in Science magazine”). The letter announcing the award came as a complete surprise, and my elation upon reading it lasted for days.

During the subsequent two years of my postdoc, Mark and I continued to explore the remarkable properties of these space-specific neurons and contrasted them with the properties of auditory neurons in the classical (“tonotopic”) pathway in neighboring subdivisions of the inferior colliculus (Knudsen and Konishi, 1978a).

At the same time, my passion for studying animal behavior resurfaced. In my spare time, I hand-raised an owl that had hatched in the laboratory’s incubator. This owl (“Dini,” short for Houdini because he kept escaping from his cage) became tame and imprinted on me. Occasionally, I would let Dini fly down the long hallways of the Beckman building, over the heads of people eating lunch. His flight was so silent that they rarely noticed this huge (1-meter wingspan) bird passing immediately overhead.

When I was in my office, Dini perched by my desk, and I soon became aware of the distinctive orientation behavior of barn owls: in response to an interesting stimulus, they turn their heads extremely rapidly and accurately toward the stimulus. For them to visually fixate the stimulus, this behavior must be accurate because their eyes are essentially stationary in the head. It occurred to me that we could harness this head-orientation behavior to assess the owl’s sound localization capabilities.

A graduate student in Jack’s lab (Gary Blasdel) had the idea of measuring the owl’s head orientation behavior with a “search coil.” At that time, search coils were being used to measure eye movements in monkeys. We attached the coil to the owl’s head. We wrapped our own coils, built the required hardware, and Gary wrote the software to calibrate and record head orientation dynamics, and accuracy. We compared orientation accuracy in response to visual versus auditory targets presented in the darkened sound chamber (Knudsen et al., 1979). Differences in visual versus auditory orientation accuracy were ascribed to errors in sound localization. Mark and I tested the effects of different types of sounds, presented from various locations, and compared sound localization behavior with the functional properties of space-specific neurons in the ICX space map (Knudsen and Konishi, 1979).

The three years that I spent with Mark transformed my approach to research. Most important, I learned the advantages and joys of collaborative research. Working with Mark and combining our strengths was fun and efficient. He revealed to me the power of quantitative behavioral studies as a tool for discovery. He also taught me the value of pursuing a dual, behavioral–neurophysiological approach to research: Results from behavioral studies guide physiological experiments toward the measurement of the most functionally important properties of neurons; conversely, the functional properties of neurons predict perceptual capacities and limitations that can be tested behaviorally.

In addition, in Mark’s lab I was steeped in neuroethology, the science of natural behavior. While I was studying barn owls, graduate students and other postdocs were studying song learning in songbirds. Mark’s office echoed with songs of developing sparrows recorded by microphones set up in their cages. We also went on regular expeditions up the coast of California to collect songbirds and into the jungles of Trinidad to study echolocating oilbirds (Konishi and Knudsen, 1979). These experiences built on similar experiences I had had in Jim’s and Ted’s labs, and I became a devout neuroethologist.

Moving to Stanford University

During my third year at Caltech, Denis Baylor visited from Stanford University to give a seminar on photo-transduction in the vertebrate retina. By chance, Mark was away at the time, so I gave Denis a tour of the lab and told him about our experiments. Unbeknownst to me, the Neurobiology Department at Stanford was searching for a new assistant professor. A week after Denis’ visit, I received a phone call from Eric Shooter, the chair of neurobiology at Stanford, inviting me to interview for the faculty position. Stanford was already in my blood: Stanford was my father’s alma mater, and I had grown up roaming its campus and cheering for its football team. I interviewed with the faculty members in this young department (Eric had founded the department just a few years before). Each member was a world-class neuroscientist: Eric Shooter, Denis Baylor, John Nicholls, Jack McMahan, and Carla Shatz. Eric was a Cambridge-trained English gentleman and all of the others had been recruited from Harvard University. As a California beach boy, I was definitely an outlier in this group. Nevertheless, they offered me the position, perhaps as a diversity appointment. For me, the position was ideal, and I accepted enthusiastically.

That summer (1979), Phyllis and I again packed up my VW bug and headed up the California coast to Stanford. This time, I also drove a large rental truck, filled with barn owls that Phyllis, Mark, and I had collected in the hills east of Caltech.

Upon arriving at Stanford, I found that there were no facilities for housing large birds. So, my first priority became building an aviary. I received approval from school authorities to construct an aviary on the roof of our research building. Building the aviary became a departmental bonding experience: the entire faculty followed our progress, and several faculty members, postdocs, and graduate students helped Phyllis and me raise the structure. I quickly learned how close-knit and supportive the Neurobiology Department was: I was not just joining a department, I was joining a family.

Within a few months, my laboratory was ready for action. Phyllis, who had trained as a neurohistologist at Caltech with David van Essen, took over as lab manager and technician. By Christmas, the owls were housed, equipment had been received, and sound chambers had been installed, one of which contained a remotely controlled, speaker-moving system, identical to the one that I had worked with at Caltech.

New Lines of Research Begin at Stanford

The first years at Stanford were golden years. Phyllis and I were the only ones working in the lab. The faculty of the Neurobiology Department, under the leadership of Eric Shooter, created a highly supportive and nurturing environment, which allowed me to thrive. Faculty members attended each other’s lectures, hosted dinners in their homes, and shared equipment and secretarial support. Faculty meetings were lively, and decisions were always reached through consensus. Once per year, each faculty member presented a research seminar to the rest of the department, at which recent experiments were discussed, data interpretations were debated, and future experiments were proposed. During the seminar, dinner was prepared and served by another lab group.

Another wonderful aspect of that early time was the process of obtaining grant support: it was simple and efficient. Acquiring funding did not require multiple resubmissions or applications to numerous foundations, as it does today. Upon arriving at Stanford, I wrote one proposal to the National Institutes of Health (NIH) and another to the March of Dimes. These proposals were funded and they paid enough to equip and run my laboratory for five-year periods. Because of the efficiency of the funding process, I was able to concentrate on what I loved doing: research.

Around the time that I moved to Stanford, my research interests began to change from how the brain organizes and processes auditory spatial information to how the brain learns to interpret auditory spatial information correctly based on experience. My new interests were sparked by two observations that I had made as a postdoc at Caltech. First, in attempting to record from neurons in the ICX space map, I would sometimes record instead from the optic tectum (OT), a beautifully laminated structure that surrounds the ICX on its lateral side. When I did, I observed space-specific auditory neurons similar to those in the ICX, but they responded also to visual stimuli. Importantly, the visual and auditory RFs of single OT units were always mutually aligned in space. This was provocative because auditory space tuning depends on the tuning of neurons to sound localization cue values (interaural time and level differences; ITDs and ILDs), whereas visual space tuning depends on topographic connections from the eyes. The question that intrigued me was: How do OT neurons become tuned to exactly the correct values of ITD and ILD so that their auditory and visual RFs mutually align in space? A related question arose from our behavioral study that showed that by plugging one of the owl’s ears (monaural occlusion), we could cause the owls to incorrectly localize sounds toward the side of the open ear (Knudsen and Konishi, 1979). The question again was: How does the brain learn the correct relationships between auditory cue values and locations in space so that an animal localizes sounds accurately? The anticipated answer to both of these questions was that the brain learns the relationships between auditory cue values and stimulus locations based on sensory experience, an expectation that turned out to be correct.

The goal of my first experiments at Stanford was to characterize and quantify the alignment of the auditory and visual space maps in the OT (Knudsen, 1982). The mutual alignment of these space maps would provide me with a metric for the accuracy of the association of auditory spatial cue values with locations in visual space in each animal. To make visual RF measurements, I fabricated a hemispheric visual screen from a 1-meter diameter Plexiglas skylight, which I calibrated to match the speaker coordinates from the speaker-moving apparatus, accurate to <1°. Phyllis and I spent many happy days and evenings plotting the auditory and visual RFs of OT units. We made marking lesions to indicate the locations of our recording sites in the OT. Phyllis processed the brains and plotted the RF locations on anatomical reconstructions of the OT. The techniques and results from this study laid the groundwork for our future studies on the role of sensory experience in aligning auditory and visual space maps in the brain.

In parallel with these neurophysiological experiments, we initiated behavioral studies, modeled on the ones I had done at Caltech with Mark, to quantify sound localization accuracy. Here, the challenge was to develop a protocol that would enable us to quantify sound localization accuracy from a single day of measurements, so that we could track changes in accuracy across days following an experimental manipulation. As we were developing this protocol, a graduate student, Steven Esterly, joined the lab.

Steve helped Phyllis with our behavioral experiments, which were yielding exciting results: Consistently, young owls raised with one ear chronically plugged adjusted to the abnormal hearing conditions and learned to localize sounds accurately with the earplug in place (Knudsen et al., 1982). In contrast, adult owls subjected to the same hearing impairment did not. We termed this early plastic period a “sensitive period” (Knudsen et al., 1984a). Interestingly, the ability of owls to recover accurate sound localization following the restoration of normal hearing (removal of the earplug) persisted to a much later age, until after the birds reached sexual maturity. We termed this period a “critical period” in the development of sound localization accuracy (Knudsen et al., 1984b). The developmental regulation of this learning process was similar to that of critical periods for song learning in songbirds, binocular vision in mammals, and language learning in humans (Knudsen, 2004). The neural mechanisms that control these critical periods were not known.

To study neural mechanisms, we needed to find a reliable neural correlate of the learning that we were observing behaviorally. The obvious metric was the mutual alignment of auditory and visual space maps in the OT. Sure enough, when I recorded from the OT of birds that had been raised with a monaural occlusion and still had the earplug in place, auditory RFs were aligned with visual RFs, indicating that the brain had learned a new mapping of cue values to locations in (visual) space (Knudsen, 1985). Consistent with this conclusion, when the earplug was removed and normal hearing was restored, auditory RFs immediately shifted out of alignment with visual RFs.

The magnitude of this shift in auditory space tuning provided a quantitative measure of the amount of plasticity (learning) that had occurred in the individual owl. Furthermore, auditory RFs gradually realigned with visual RFs over a period of days following earplug removal, at a rate that matched the rate at which birds recovered accurate sound localization behavior. Importantly, these large adaptive shifts of auditory RFs occurred only when owls were monaurally occluded early in life, during the behaviorally defined sensitive period. We realized that we had found an easy-to-measure, reliable neural correlate of sound localization plasticity.

The Hunt for an Instructive Signal

At this stage, I began thinking about the sources of information that the brain might use to guide adaptive adjustments in auditory space analysis. The obvious candidate was vision: although the brain has access to spatial information from other sources, the spatial information provided by the visual system is by far the most reliable and precise. Reinforcing this intuition, we had noticed that in the auditory maps of the ICX and OT, the representation of frontal space was greatly magnified in a way that was not expected from the properties of auditory spatial cue values but that was expected from a retinotopic template of the world (Knudsen, 1982).

To test for an instructive influence of visual input on auditory space processing, Phyllis and I began studying the effects of altering vision (either by blocking vision or by displacing vision with optical prisms) on the adjustment of sound localization behavior. The idea of using displacing prisms originated from Jack Pettigrew (at Caltech), who used light-weight Fresnel prisms to correct for strabismus in his visual experiments on cats. I decided to try these prisms on owls. We built spectacle frames out of welded wire and metal washers, and cemented the frames to the owl’s skull.

The initial experimental strategy was to raise owls with one ear occluded. Then, remove the earplug to induce a systematic sound localization error, and measure the effects of blocking vision (black plastic discs inserted into the frames) or displacing vision (matched prisms inserted into the frames) on the recovery of accurate sound localization behavior. The results demonstrated clearly that with vision blocked, sound localization errors remained uncorrected, and that experience with displaced vision caused sound localization to adjust to match the displacement of the visual field caused by the prisms (Knudsen and Knudsen, 1985).

In the next round of experiments, we simply raised owlets wearing displacing prisms, without prior monaural occlusion. Amazingly, these birds adjusted sound localization to match the displacement of the prisms: they learned to orient the head to the side of an auditory target so that they would see the target through the prisms, even though head orientations to auditory targets had initially been accurate (Knudsen and Knudsen, 1989). These results demonstrated the dominant role of vision in calibrating the owl’s responses to auditory spatial cues.

While Phyllis, Steve, and I were studying ways to induce adaptive plasticity in owls, John Middlebrooks joined the lab as my first postdoc. His interests were in space coding in the mammalian homologue of the OT, the superior colliculus (SC). He built apparatus to record from cats (the species he had studied as a graduate student), and tested cat SC units with the same free-field sound system that we were using to study owls. He found auditory space tuning and mutual alignment of auditory and visual space maps in the SC, analogous to the properties we were observing in the owl OT (Middlebrooks and Knudsen, 1984, 1987). John’s results strengthened the view that multisensory space integration is a salient function of the OT/SC that is shared across vertebrate species.

After six wonderful years at Stanford, my lab was still small. Nevertheless, the progress we had made in understanding the powerful influence of sensory experience in shaping the brain’s processing of auditory spatial information had been sufficient for me to be promoted and granted tenure in my department. Meanwhile, as a balance to research and teaching, Phyllis, Steve, and I played volleyball and went scuba diving and sailing, Phyllis and I joined John and his fiancé for dancing, and I reserved early Wednesday mornings for surfing.

The Laboratory Team Grows

In the 1980s, three new lab members, a graduate student (Sascha du Lac), and two postdocs, (Tom Masino and John Olsen) brought fresh ideas, techniques, and energy to the lab, and the culture in the lab was greatly enriched. We now had enough people to begin weekly lab meetings, and the topics of daily discussions ranged widely from acoustics to how the brain plans and executes movements.

New lines of research were initiated, all related to the space map in the midbrain. One line of research was pioneered by Sascha and Tom. They were interested in understanding how the midbrain represents instructions for orientating the head toward attended stimuli and how those instructions are translated into premotor signals in the brainstem. To address these issues, they developed techniques for electrically microstimulating in the brains of owls that were free to move the head.

Microstimulation applied to the owl’s OT resulted in a rapid orienting movement of the head. Using this preparation, Sascha demonstrated that the size and direction of the evoked head movements change systematically with the site of stimulation across the OT, revealing a “motor map” of orienting movements, and this motor map is in register with the visual and auditory maps of space (du Lac and Knudsen, 1990). Moreover, by raising owls with vision blocked, she found that the motor map, like the auditory map, is adjusted and calibrated by early visual experience (du Lac and Knudsen, 1991; Knudsen et al., 1991).

Simultaneously, Tom discovered that, like the eye movement commands from the SC in monkeys, the head movement commands from the OT in owls are transformed by the brainstem into the horizontal and vertical components of the desired movement (Masino and Knudsen, 1990). This was surprising because head movements, unlike eye movements, involve many muscle groups with various pulling directions, none of which align with these Cartesian directions. This result indicated, therefore, that the translation of topographic motor commands into horizontal and vertical vector components is a strategy employed by the brain to orient gaze, regardless of the body parts used to accomplish the movements.

During this time, John Olson initiated a line of research that was to become the backbone for future research in my lab. John was interested in exploring how the binaural spatial cues (interaural time and level differences, ITD and ILD) are represented across the OT to create a space map. Answering this question required that we develop techniques for delivering sounds through earphones (to manipulate frequency-specific ITD and ILD cues independently and parametrically). To accomplish this, we pushed the capacities of our computers to synthesize and systematically vary microsecond differences in interaural timing and decibel differences in interaural level. We spent a year searching for the best hardware for delivering sounds directly to the owl’s ear canals and writing the software necessary to generate, calibrate, and systematically manipulate the sound. Once these tools were in hand, John found that OT neurons are sharply tuned for both ITD and ILD, that neuronal tuning to ITD and ILD predict their spatial tuning, and that the cue values to which neurons are tuned change systematically across the OT in a pattern that matches the way in which these values change across space for barn owls (Olsen et al., 1989).

The tools that we developed to enable John’s research were essential to the next era of research in the lab: exploring the sites and mechanisms of adaptive auditory plasticity in the brain. Previously, our assessment of adaptive changes in the owl’s brain relied on measurements that we made using the moveable, free-field speaker. This worked fine for testing neurons that were tuned for space, as in the ICX and OT. However, neurons in the classical auditory pathway that provide input to these structures are tuned, instead, for sound frequency and are organized in frequency maps (“tonotopic maps”), not in space maps. To identify sites along the auditory pathway where adaptive plasticity occurs, we needed to be able to measure changes in the tuning of neurons to frequency-specific ITDs and ILDs. Thanks to John’s project, we now had this capability.

Toward the end of this period, in 1987, I was offered a professorship at University of California San Francisco. The systems neuroscience faculty at UCSF was large, cooperative, and among the best in the world. At Stanford, Carla Shatz and I were the only systems neuroscientists in my department. Although Carla and I greatly enjoyed working and teaching together, the opportunity to team up with the UCSF faculty was attractive. As inducements to keep me at Stanford, my department offered me a promotion and, more important, a commitment to hire another systems neuroscientist to our faculty. At this time, a group of neuroscientists, including Phyllis, Carla, Bill Newsome, and myself, were rooming together at a winter neuroscience conference. By chance, Bill mentioned to Phyllis that he was not content with his job on the east coast. I had known Bill since 1978, when I had been a postdoc and he a graduate student at Caltech. Both Carla and I knew Bill to be a deep thinker and a brilliant scientist. We brought this news back to Stanford and recommended him enthusiastically to our fellow faculty members. Bill came for an interview and was hired. Recruiting Bill to Stanford provided him the resources he needed to realize his full potential as a world leader in neuroscience. Helping to bring Bill to Stanford turned out to be among my most consequential contributions to my department, Stanford University, and the field of neuroscience.

During this period, Phyllis and I adopted our two sons, Chris in 1986 and Keith in 1989. Our expanded family brought us a whole new world of joys, adventures, and challenges, and enriched our lives immensely.

Exploring Mechanisms of Learning

Over the following decade (1990–2000), the lab continued to grow and mature. With increasing lab size came the establishment of new traditions. Early on, Steve had been a scuba diver, sailor, and volleyball player, so Phyllis and I had enjoyed sharing these leisure-time activities with him. As the lab group expanded, communal activities became regular events: volleyball or ultimate Frisbee on Friday afternoons, canoeing the Russian River on summer weekends, skiing in the Sierra Nevada in the winter, and backpacking in the summer. We also enjoyed sailing trips to the Channel Islands (just off the California coast near Santa Barbara). There, we lived off the land, diving for abundant fish, abalone, lobsters, and scallops. Those were the days!

Back in the lab, regular Friday morning lab meetings were instituted for discussing ideas, recent research progress, and publications. We also established four awards: the “Phineas Gage award” for developing a new lab technique; the “dimpled-brain award” for a major discovery; the “golden owl award” for a paper accepted for publication; and the “biggest brain award” for a graduate student passing the qualifying exam. A perpetual trophy was associated with each award. Every few months, we would go to lunch at a restaurant selected by the winner of the golden owl award, the trophies would be handed out, the winners would explain what they had accomplished, and we would pose for photographs. The winners displayed their trophies proudly (?) by their desks until the next award luncheon. These events contributed to our esprit de corps, and they brought me joy.

Our excellent lab morale, although reinforced by social activities, was anchored in the various veins of exciting research that we had begun to mine. We had already established several experimental methods for reliably inducing large, adaptive changes in both sound localization behavior and the functional properties of neurons in the midbrain. Obvious next questions included the following: Where in the brain does the learning take place? What cellular mechanisms underlie the learning? Does the forebrain contribute to the learning?

Michael Brainard, a graduate student, took up the challenge of discovering where in the brain learning takes place. Enabled by our new technology for measuring neural tuning to frequency-specific ITD and ILD, Michael demonstrated that the first site where prism experience alters the brain’s representation of binaural cue values is in the ICX, where the midbrain translates auditory cues into a space map (Brainard and Knudsen, 1993). He went on to explore the dynamics of the experience-driven changes in neuronal tuning and the effects of age on these dynamics (Brainard and Knudsen, 1995).

Joachim Mogdans, a postdoc, found that learning in response to experience with monaural occlusion occurs, at least in part, in the classical (tonotopic) auditory pathway, at the site where inputs from the two ears are first compared to measure frequency-specific ILDs (Mogdans and Knudsen, 1994). Thus, his results showed that the site in the brain where plasticity occurs depends on what the brain needs to learn: Experience with monaural occlusion, which changes the values of ITDs and ILDs, causes adjustments at early sites in the pathway where binaural cues are measured. In contrast, experience with displacing prisms—which do not alter the auditory cue values themselves but, instead, change the relationship between normal cue values and locations in visual space—causes adjustments at later sites in the pathway where auditory-visual associations are established.

In 1994, Dan Feldman joined the lab as a graduate student and initiated an exploration of cellular and molecular mechanisms that underlie the adaptive plasticity in the ICX. Dan began by demonstrating anatomically that neurons bringing frequency-specific information to the ICX acquire new patterns of axonal projections and that the normal and learned projection patterns coexist in the ICX of prism-reared owls (Feldman and Knudsen, 1997). He then developed techniques to manipulate specific types of neurotransmitter receptors with drugs delivered with spatial precision (micro-iontophoresis). This technique enabled him to show that the newly learned responses of ICX neurons are mediated by a special class of neurotransmitter receptors (NMDA receptors) (Feldman and Knudsen, 1998).

While these discoveries were being made in the midbrain pathway, a postdoc, Yale Cohen, explored how the forebrain represents auditory spatial information (Cohen et al., 1998). He joined forces with Tom Masino to identify the forebrain area that controls voluntary changes in gaze direction in owls (analogous to the frontal eye fields in the prefrontal cortex of primates) (Knudsen et al., 1995). Using the same top-down approach that we had used earlier in the midbrain pathway, he studied the representation of auditory spatial information in the forebrain pathway that leads to this area. He found that in the forebrain, neurons are grouped according to their spatial tuning in a patchy representation of space, but they do not form a topographic map of space like the one created in the midbrain (Cohen and Knudsen, 1995, 1999).

Another cohort of superb graduate students and postdocs joined the lab during the latter half of this decade, bringing with them new ideas and interests. To challenge the capacity of the auditory system to make detailed adjustments in its tuning to ITD and ILD, Josh Gold developed an ingenious passive acoustic filter, which he implanted in one of the owl’s ears, that altered the timing and level of sound reaching that ear in a frequency-dependent manner. He found that in young owls, experience with this device caused ICX neurons to restore a map of space by adjusting their tuning to ITD and ILD in a frequency-specific manner, so that neurons became tuned to the highly unnatural combinations of cue values that the owls experienced (Gold and Knudsen, 2000a). In addition, he showed that this frequency-specific adaptive tuning results from changes in connectivity within the IC (Gold and Knudsen, 2000b).

Weimin Zheng, a postdoc, investigated molecular mechanisms that underlie prism-induced auditory plasticity. He blocked inhibition in the ICX of prism-reared owls that were expressing a learned space map, thereby unmasking excitatory influences on these neurons. He showed that excitatory connections that support tuning to normal cue values (the original space map) coexist with learned excitatory connections that give rise to the learned space map (Zheng and Knudsen, 1999). After learning, however, responses to the normal connections are suppressed by inhibitory GABAa receptor currents. Thus, in prism-reared owls, the brain uses GABAergic inhibition to select which of the alternative space maps (normal versus learned) is functionally expressed.

Peter Hyde, a graduate student, hunted for the source of the instructive signal that guides the formation of the learned auditory connections in the ICX. He discovered, using anatomical techniques, that a topographic pathway projects back from the OT (which contains a topographic visual map of space) to the ICX (Hyde and Knudsen, 2000). He found that activity in this pathway acts as a template for guiding the formation of auditory connections in the ICX, thereby customizing, for each individual, auditory cue-location associations in the ICX (Hyde and Knudsen, 2002).

Meanwhile, Will DeBello, a postdoc, characterized anatomically the axon remodeling that gives rise to the learned space map in the ICX (DeBello et al., 2001). In addition, he showed that a second site of plasticity exists in the midbrain pathway: in the OT itself. There, experience aligns the auditory space map sent from the ICX with the OT visual space map (DeBello and Knudsen, 2004). Developmentally, this higher-level plasticity continues long after plasticity in the ICX has become severely restricted because of its sensitive period.

While these exciting discoveries were being made in the lab, the neuroscience community at Stanford was expanding dramatically, with excellent neuroscientists being hired into many departments and schools across the university. In addition, Stanford’s Neuroscience Graduate Program, which initially was organized and run by the faculty in my department, became more formalized, largely because of the concerted efforts of Howard Schulman.

In my small department, directing the graduate program, running the core course in neuroscience for the medical school, and chairing the department were essential functions that each senior faculty member was expected to perform in turn. I was happy to do my part. So, in 1998, I took over running the Neurosciences Graduate Program from Howard. This was a mixed blessing. On the one hand, I enjoyed interacting with the exceptionally talented students in the Graduate Program, and I was able to have a major influence on their experiences. On the other hand, the responsibilities—including organizing events, implementing policies, arbitrating disputes, and writing training grants—all demanded time. As a result, my time in the laboratory dropped precipitously.

Final Studies on Mechanisms of Learning

As director of the Graduate Program, I benefited greatly from knowing the incoming class and was able to use that knowledge to recruit three stellar students to my lab: Greg Miller, Brie Linkenhoker, and Joseph Bergen. In addition, a bright young postdoc, Yoram Gutfreund, joined the lab.

Greg was interested in searching for evidence of experience-dependent plasticity in the forebrain auditory pathway. He exploited sensory manipulations that we had developed to study plasticity in the midbrain pathway: early experience either with the acoustic filtering device invented by Josh or with displacing prisms. He found that auditory experience causes adaptive changes in the auditory thalamus of the forebrain pathway, whereas visual experience does not (Miller and Knudsen, 2003). Thus, the site of adaptive plasticity in the forebrain depends on the nature of the sensory disruption, as it does in the midbrain.

Brie was interested in studying adaptive plasticity in the midbrain pathway of adult owls. Contrary to our previous observations, she found that adult prism experience can, indeed, drive large changes in auditory spatial tuning in the ICX. The key is to impose the sensory disruption (prismatic displacements of the visual field) in small, incrementally increasing steps (Linkenhoker and Knudsen, 2002). Even with incremental learning steps, however, the overall changes in adults are smaller than those that are induced in juveniles by a single large disruption, reflecting a capacity for plasticity that appears to be unique to the young, developing brain. Brie also confirmed anatomically that the learned circuitry in the ICX that is formed in response to early prism experience, persists in adulthood even when it has not been used for long periods (after prisms were removed). This preserved learned circuitry can be rapidly reactivated by experience in adulthood, should it become adaptive once again (i.e., when the same prisms are remounted on the owl) (Linkenhoker et al., 2005). This result is reminiscent of the effects of early language learning on language acquisition in adult humans.

Yoram Gutfreund began studying the signals that instruct learning in the ICX. Peter Hyde had demonstrated previously that a topographic, instructive pathway projects from the OT to the ICX. Yoram used pharmacology to open a gate in the OT that allowed for this instructive signal to be transmitted back to the ICX. He did this by blocking inhibition focally in the OT (using iontophoretic application of a GABAa receptor blocker). Opening this inhibitory gate caused space-specific visual signals to appear in the ICX (normally, ICX neurons respond only to auditory stimuli) (Gutfreund et al., 2002). The receptive field location of the gated visual signals in the ICX matched perfectly the auditory spatial tuning at the recording site in the ICX, implying that the gated signals act as a topographic template for shaping auditory spatial tuning. Yoram then showed how this gated visual signal has the properties required for instructing the selection of auditory inputs in the ICX, based on synchronous auditory-visual signals (Gutfreund and Knudsen, 2006).

Joe Bergan was the last member in my lab to study experience dependent plasticity. Inspired by Brie’s results indicating that adult owls retain a substantial capacity for adaptive plasticity, Joe tried a new approach to induce plasticity in adults: he exposed owls to strong prisms, which caused large auditory-visual spatial mismatches, but he forced them to hunt and capture live mice to survive. He found that the auditory spatial tuning of OT neurons shifted significantly further (by a factor of 5) in birds that had to hunt versus in those that were fed in the traditional way, with dead mice (Bergan et al., 2005). The only difference in experience between these two groups of owls was the short time (seconds to minutes) that hunting owls spent each day, tracking and attacking live mice. Although several factors are likely to contribute to this increase in learning, an obvious factor is the heightened attention and arousal of an owl while it attempts to fuse auditory and visual spatial information from a scurrying mouse. The results of Joe’s experiments started me thinking about an entirely new topic: how attention might enhance learning and adaptive plasticity in adult owls.

Expanding Horizons and Responsibilities

Over the next decade (2001–2010), my responsibilities to my department, university, and national scientific community continued to grow. In 2001, I stepped down as director of the Neurosciences Graduate Program and took over as chair of my department. Dealing with departmental issues demanded even more of my time. As a result, for the first time in my scientific career, I was not able to carry out experiments. On the negative side, this meant that I no longer experienced the thrill of discovery, and I was not able to test the viability of new lines of research that could be offered to incoming graduate students and postdocs. On the positive side, my absence from the lab freed lab members to try risky experiments themselves and to send the research in my lab in entirely new directions.

Although serving as chair of my department was an enormous distraction from research, it was time well spent. I learned in detail about my department, its staff, students and faculty, budgets and space allocations, and plans for the future of the school and university. My greatest satisfaction as chair derived from overseeing the hiring of new faculty members: we hired one new member every year for four of the five years that I served as chair. In the process, I learned the background, accomplishments, and future goals of each of these superb young scientists, who represented the future of my department. Our practice of having the chair rotate among faculty members contributed greatly to the cooperative atmosphere in the department. Among other things, it gave every faculty member a deep appreciation for the essential work that administrators do to make the pursuit of science and teaching possible for the rest of us, it distributed administrative expertise throughout the faculty, and it increased empathy and tolerance for the challenges faced by the chair.

During this period, I also joined the National Scientific Council on the Developing Child, which turned out to be the most rewarding and enjoyable committee experience of my career. The council was composed of a group of 15 experts in the fields of brain development, child psychology, and economics. It was led by Jack Shonkoff, an expert in children’s health and development, who was passionate about bringing the latest advances in neuroscience and psychology to the benefit of children through changes in public policy. The council was special because we came from different scientific backgrounds and academic cultures, yet we all shared Jack’s passion. Twice each year, we gathered at a wonderful location (different each time), where we engaged in intense discussions, lasting several days. We presented to each other our latest research on early brain or child development, we learned from professionals how to communicate our findings effectively to policymakers and to the public, and we planned public seminars and the writing of research and review papers. Our mission was to act strictly as knowledge brokers (we never advocated for any particular public policy): we provided the best scientific knowledge about the effects of early experience on the development of the brain and behavior. By not advocating for specific policies, we maintained our credibility with, and access to, members of all political parties. Through this experience, I became keenly aware of the importance of communicating the implications of the scientific discoveries made in my lab to the general public and, in particular, to policymakers. A review paper that I wrote in collaboration with this council (Knudsen et al., 2006) was the most satisfying to write of all my papers.

Research Focus Changes from Learning to Attention

While I was busy running my department, research interests in my lab began to shift. Ilana Witten, who joined the lab as a graduate student in 2002, introduced computational modeling to our research armamentarium. Whereas I tend to think in pictures and patterns, Ilana analyzed experimental results in mathematical constructs. She applied her mathematical talents to her research: exploring mechanisms that could account for the dynamic properties of the auditory space map. For example, she and Joe Bergan observed dynamic shifts in the locations of auditory RFs in the OT space map in response to moving stimuli (Witten et al., 2006). These RF shifts caused the space map to represent the future location of the moving stimulus, information that is essential for an animal to orient accurately to a moving stimulus despite delays caused by the brain’s processing of sensory information and motor planning. Ilana modeled the dynamics of the excitatory and inhibitory influences that result from spatially organized, classical RFs (RFs with excitatory centers and inhibitory surrounds) and showed that these dynamics, which are common to topographic sensory representations in the brain, result in predictive shifts in RF locations. She also modeled the gradual shifts in auditory RF locations that result from sensory experience and demonstrated that a simple learning rule (the “Hebbian rule”) can account for the instructive influence of visual inputs (Witten et al., 2008). Her model showed that an instructive input to a network does not need to have specialized anatomical or genetic properties, but instead can exert its guiding influence through the action of this common learning rule. The mechanistic insights that I gained from Ilana’s modeling work convinced me of the importance of including computational modeling as a research tool going forward.

Joe Bergan’s experiments, which had revealed substantial space map plasticity in adult owls, started me thinking about “attention” and how attention might increase learning and adaptive plasticity in adults. A postdoc, Dan Winkowski, shared my interest. Dan developed electrical microstimulation techniques that enabled him to explore the influence of descending signals from the forebrain (from a gaze control area called the arcopallial gaze field, AGF) on the representation of sensory information in the midbrain space map. The equivalent area in primates (called the frontal eye field) had just been shown to control spatial attention in monkeys. Dan found that a signal from the AGF (evoked by electrical microstimulation) representing a particular location, does not drive neural responses in the midbrain space map, but it greatly enhances sensory responses to stimuli at that location, and it simultaneously suppresses responses to stimuli at all other locations in the map (Winkowski and Knudsen, 2006, 2007). This effect is reminiscent of Francis Crick’s “attentional spotlight.” These top-down forebrain effects share many of the properties of top-down effects that have been reported in the visual cortex of monkeys when they attend to a stimulus (Winkowski and Knudsen, 2008). Moreover, with Dan’s microstimulation methodology, we were able to manipulate the location and timing of these modulating signals precisely.

Our previous anatomical studies had shown that the AGF projects both to the OT and to a cholinergic nucleus in the midbrain tegmentum called the nucleus isthmi pars parvocellularis (Ipc). The Ipc, which interconnects reciprocally and topographically with the OT and is equivalent to a portion of the parabigeminal nucleus in mammals, had been shown to drive periodic bursts of OT spikes in response to visual stimuli, and it was hypothesized that the Ipc participates in the analysis of visual information. Kristin Maczko, a graduate student, decided to test this hypothesis. Her experiments revealed that Ipc neurons respond to both auditory and visual stimuli from the same location in space (Maczko et al., 2006), a property that is inconsistent with its hypothesized role as a processor of visual information. Instead, the encoding of stimulus location independent of stimulus modality is consistent with a role of the Ipc in regulating sensory responsiveness in a space-specific manner (i.e., acting like an attentional spotlight).

The Ipc is a central component in a midbrain network, found in all vertebrate species, that interconnects extensively with the OT. The unusual patterns of anatomical connectivity within this network suggest that it generates an attentional spotlight like the one proposed by Francis Crick for mediating spatial attention. The promising results from Dan and Kristin’s experiments were consistent with this hypothesis, and they focused my interest on this network.

FINDING NEW SOURCES OF RESEARCH FUNDING

By 2005, the composition and social dynamics of the lab group had changed. Lab members were no longer ocean junkies but, instead, loved the mountains. We enjoyed skiing trips in the winter and backpacking trips in the summer. The traditions of luncheons for the awarding of lab trophies and Friday evening games continued. To maintain balance in my life, I surfed on Wednesday mornings, although a near-drowning experience made me realize that it was time to stop riding big waves. I sailed and backpacked with Phyllis and my two sons in the summer, and I started playing basketball (I am 6’ 3”) on a weekly basis.

By this time, mechanisms of spatial attention had become the theme of the lab’s research. With the transition to studying “attention,” a new cohort of students and postdocs began joining the lab all interested in the question of how the brain selects and tags information in real-time for differential processing. This change in research focus was energizing. I immersed myself in the literature on attention research. I found that this field was rich in descriptions of the amazing phenomenology associated with attention, but it had little to say about the neural circuits and mechanisms that actually perform the selection of information or that enhance neural responses representing the selected information. After studying this literature, I wrote my first paper on this topic (Knudsen, 2007) in an attempt to define the various components of attention that needed to be explained mechanistically.

The experiments that excited me now were completely unrelated to the kinds of experiments that we had conducted in the past. It soon became apparent that my long-standing grant support could not be applied to the pursuit of these experiments and that I would need to acquire funding from new NIH study sections and private foundations. This turned out to be a challenge. Over the previous 25 years, I had applied to a single NIH study section and to certain private foundations. They knew my work and had invested in it. I had routinely written each application once, never needing to resubmit. Moreover, the grant reviewers in my previous research field were accustomed to proposals that employed various species as experimental animals to take advantage of evolutionary specializations that facilitated discovery. In contrast, research on attention was dominated by scientists who studied the phenomenology of attention in humans and nonhuman primates. When I applied for funding to study circuit mechanisms of attention in the midbrain of birds, the applications were reviewed by scientists who had little appreciation for, or knowledge of, brain evolution and comparative neuroscience. The dominant opinion was that selective attention was a capacity that could be explored only in the forebrain of primates or, perhaps, rodents. I was disappointed and saddened by this mind-set. To me, it is obvious that the capacity for selective attention must have evolved early, enabling animals to make adaptive decisions in complex environments, and that the diversity of species offers unique opportunities to learn about the neural mechanisms that mediate this amazing executive capacity.

It took six long years and the publication of 10 papers from my lab to finally convince NIH reviewers of the validity and promise of our novel approach and to award funding for it. Fortunately, my troubles with finding new sources of funding coincided with me stepping down as chair of my department, thereby providing me the time necessary to pursue new funding sources and to do experiments.

TESTING THE MIDBRAIN NETWORK FOR A ROLE IN CONTROLLING ATTENTION

An essential capability of a network that controls spatial attention is that it be able to select one from among many competing stimuli for differential processing. In our previous work, we had always presented only a single stimulus at a time to the animal, a highly unusual condition in nature. Now we asked: When multiple stimuli are present simultaneously, how does the midbrain network pick one location to direct an animal’s gaze and spatial attention?

Stimulus selection requires a competitive process, a competition to identify the stimulus that is of highest priority at any moment. To study stimulus competition, we needed to invent an experimental protocol that could parametrically manipulate stimulus priority, elicit consistent neural responses across many stimulus repetitions, and quantify the results. Two postdocs, Shreesh Mysore and Ali Asadollahi, took on this challenge. The goal was to find a visual stimulus parameter that, when increased, systematically increased the strength (“salience”) of a stimulus, and to which OT neurons did not adapt (responses in the OT typically adapt drastically after just one or a few presentations of a given stimulus). Only then could we make repeated measurements of the effects of stimulus competition.

Shreesh and Ali devoted more than a year to perfecting such an experimental protocol. The solution was to use a looming dot—a dot that grows in size as though it were approaching the animal—as the stimulus. They changed the speed of the loom to manipulate the priority of the stimulus. They found that the strength of OT responses increased systematically with the speed of loom and that OT responses to looming stimuli persisted across many stimulus repetitions. The effectiveness of this stimulus parameter makes sense, given that a looming stimulus predicts an animal’s collision with the stimulus, and the speed of the loom correlates with the time to collision.

Shreesh and Ali measured the effects of competition between two stimuli by parametrically varying the relative speeds of simultaneously looming dots while recording the responses of OT neurons that were tuned to the locations of the dots. By applying this stimulus protocol, Shreesh and Ali observed that the OT space map indicates the stronger of two stimuli, even when the difference between their strengths is extremely small, and represents the “highest priority stimulus” categorically with differentially strong and periodic bursts of spikes (Mysore et al., 2011).

With this competition protocol, we were able to systematically control stimulus selection by the network. Our goal then became understanding the mechanisms that mediate this selection. As mentioned previously, the OT is densely interconnected with several nuclei located in the floor of the midbrain, nuclei that are referred to collectively as the isthmic nuclei. Each of these nuclei receives topographic input from the OT. One of them returns inhibitory (GABAergic) input broadly to the space map. Others return cholinergic input to precisely the location in the OT that provides its input (the Ipc is one of these cholinergic nuclei). Together, these structures form the core of the midbrain selection network (Knudsen, 2011).

Shreesh focused on the GABAergic nucleus, called the nucleus isthmi pars magnocellularis (Imc). The Imc receives topographic input from the OT and sends inhibitory output broadly to the OT. Based on its atypical pattern of interconnections with the OT, previous scientists had hypothesized that the Imc mediates global inhibition across the entire OT space map. Exploiting our competition protocol, Shreesh tested this hypothesis. He combined physiological measurements in the OT with precise, focal inactivation of the Imc, and computational modeling to reveal how this inhibitory circuit mediates stimulus selection (Mysore and Knudsen, 2012). He went on to show that this same inhibitory circuit is critical both to stimulus competition and to forebrain biasing of stimulus competition in selecting the highest priority location (Mysore and Knudsen, 2013, 2014).

At the same time, Ali was studying the role of one of the network’s cholinergic nuclei, the Ipc. He combined physiological recordings with focal inactivation of the Ipc to demonstrate that this cholinergic circuit is responsible for both amplifying OT responses to the selected stimulus and causing them to be periodic. Amplified periodic responses in the OT tag a location in the map as the selected location (Asadollahi et al., 2010; Asadollahi and Knudsen, 2016).

Brain Slices: A New Frontier

The results coming from Kristen’s, Shreesh’s, and Ali’s experiments sparked my desire to understand the underlying cellular and molecular mechanisms by which the midbrain network performed competitive stimulus selection. Dissecting molecular mechanisms in a living animal (in vivo) is difficult, but it is readily feasible in slices of the brain that are studied in a dish (in vitro). However, I had no expertise in, or experience with, brain slice technologies. Moreover, such experiments require several brains per week, far exceeding our supply of barn owls.

Alex Goddard solved these problems. I recruited Alex as a postdoc with expertise in in vitro techniques and an interest in understanding cellular mechanisms of network computations. He recognized that domestic chicks are readily available commercially and, like other birds, they possess a highly differentiated midbrain network. He soon discovered that by slicing the chick brain at a specific angle, all of the components of the midbrain network and their anatomical connections could be maintained intact in a single brain slice.

Just as Alex was developing in vitro slice techniques using chicks, a graduate student, Devarajan Sridharan (“Sridhar”) was characterizing a conspicuous, periodic component of sensory responses (25–50 Hz; called “gamma oscillations”) to visual and auditory stimuli in the OT of barn owls (Sridharan et al., 2011). Alex and Sridhar teamed up to study the source and molecular mechanisms of these oscillations in the chick brain slice. They found that oscillations, identical to those evoked by sensory stimuli in vivo in owls, were evoked by electrical microstimulation of retinal afferents in chick brain slices. They localized the source of the gamma pattern generator to layer 10 in the OT; they revealed the specific roles of various neurotransmitter receptors in regulating the frequency, amplitude, and persistence of the oscillations; and they showed the contribution of the Ipc cholinergic feedback loop to the amplification of the oscillatory OT activity (Goddard et al., 2012). Astra Bryant, a graduate student, went on to identify the specific type of cholinergic receptor that regulates the amplitude of the response oscillations in the OT (Bryant et al., 2015).

Again exploiting the chick slice preparation, Alex studied details of the inhibitory circuitry in the Imc, circuitry that is essential to competitive stimulus selection by the network. As predicted by Shreesh’s computational models, he showed that inhibitory neurons in the Imc mutually inhibit each other on a global scale, causing stimulus selection to operate across all of space and enabling high resolution selection across wide ranges of absolute stimulus strengths (Goddard et al., 2014).

During this final decade of research, the atmosphere in the lab was particularly stimulating. We were exploring the nexus of spatial attention and the midbrain network at multiple levels: molecular, cellular, circuit, network, behavioral, and computational. Discussions in the lab ranged across these levels, and experimental results from one level directly informed experiments at the others. These were exciting times!

The culture in the lab had also changed. Nearly all of the lab members were married, and two of them had children (as did Phyllis and I). Although they all enjoyed the outdoors, several were not experienced in water or mountain sports. Consequently, lab excursions tended toward family activities, such as picking berries and making jam, observing elephant seals on the Pacific coast, ice skating, swim parties, and picnics.

Behavioral Measures of Attention

Together, the results from our in vivo experiments on owls, in vitro experiments on chick brain slices, and computer modeling studies gave me a satisfying degree of understanding of how the midbrain network selects the highest priority location, and how it amplifies and makes rhythmic the activity associated with that location. The mechanisms we had found were consistent with, and could account for, many of the signature properties of spatial attention reported in primates (Knudsen, 2012). The critical unanswered question was: Do these midbrain circuits actually control spatial attention? The answer to this question required that we study the animal’s behavior.

While we had been pursuing physiological and computational studies, Phyllis had worked on developing a behavioral assay to measure spatial attention in barn owls. Among the obstacles that she faced was that each owl had to be hand-raised to be tame enough to be handled and trained. More problematic, she could not find a reward protocol that would induce them to respond to many stimulus presentations reliably every day. Meanwhile, an inexperienced undergraduate student was able to train chickens easily to perform hundreds of sophisticated (delayed match-to-sample) tests reliably in a single test session after just a few weeks of training.

Realizing the necessity for having behavioral assays to measure attention and the many practical advantages of working with chickens over owls, I finally decided to switch all of our experiments to chickens. This was a sad realization because chicks, although cute, do not have the majesty or cachet of owls. Moreover, switching to chickens required a huge effort: a redesign of the laboratory equipment from the ground up. We had to make a new brain atlas for targeting structures; replace our stereotax and recording equipment; and install new behavioral apparatus, including eye-tracking equipment (chickens move their eyes extensively, unlike barn owls). In addition, baseline neurophysiological measurements had to be repeated in chickens. Compounding our challenges, my plan to switch from owls to chickens and from auditory to visual testing was not received well by granting agencies: I had no track record in either domain. Fortunately, Stanford University granted me seed funding, enabling me to embark on this new direction of research.

Once the laboratory was rebuilt to accommodate chickens, two postdocs, Sridhar Devarajan (who had been a graduate student in my lab) and a new postdoc, Jason Schwarz, pushed forward with studies of selective attention in chickens. Being a domesticated species, the chickens were calm and easy to train. More important, they were able to learn difficult tasks, allowing us to measure their performance on tests that were comparable to those used to measure spatial attention in primates. The tasks measured their ability to make perceptual decisions about stimuli (the orientation of small grids on a computer screen) presented at various locations in space, with and without spatial cueing, and with and without distracting stimuli at other locations. In addition, Sridhar developed a new data analysis framework that allowed us to differentiate between attention-dependent effects on an animal’s sensitivity to stimuli and changes in the animal’s bias to respond to stimuli at a particular location (Sridharan et al., 2014a). Using these behavioral tests and this analysis framework, we found that the phenomenology of spatial attention in chickens and primates is remarkably similar (Sridharan et al., 2014b; Sridharan et al., 2017).

Demonstrating a Causal Role of the Midbrain Network in Spatial Attention

We now had a behavioral paradigm that would allow us test for a causal linkage between the midbrain selection network and spatial attention. Our strategy was to make small lesions in the OT or Ipc (the cholinergic feedback circuit), at sites representing a known location, and then test the ability of the animal to attend to that location (to identify the orientation of a small grid at that location). It took several years and the dedication of two tireless technicians, Deepa Ramamurthy and Suzanne van Winden, to help Phyllis train the birds and collect the data on this complicated task. Jason Schwarz placed the lesions in the OT or Ipc of each bird. By the time we were testing the last of these birds, all members of my laboratory, including Sridhar and Jason, had moved on to other positions. For the final year of the project, Phyllis and I worked alone in the lab, as we had when we first arrived at Stanford, 37 years before. Once we had finished collecting and analyzing the data, I concentrated on writing up the results.

Drafting this final research paper was a pleasure. As mentioned previously, I enjoy writing, and the results of this study were clear: a focal lesion in the OT space map rendered birds incapable of deciding the orientation of a visual grid specifically at the lesioned location (Knudsen et al., 2017). This result is critically revealing because the information required by the brain for making decisions about grid orientation is processed in the bird’s forebrain visual pathway and not in the midbrain pathway (as is true also in mammals). The experiments demonstrate, therefore, that the OT in chickens, like the superior colliculus (the equivalent structure) in monkeys, controls the routing of forebrain sensory information to networks that make cognitive decisions. That is, it controls selective spatial attention.

This conclusion led me to the realization that the primary function of the OT, throughout evolution, is to act as a “location selection mechanism” for guiding spatial attention and the direction of gaze (Knudsen and Schwarz, 2017). Commanding orienting movements for redirecting gaze, generally considered to be the primary function of the OT, is actually secondary to location selection for attention. That is, the OT is constantly directing the spatial attention of an animal to top priority locations, but it only issues commands for orienting movements to those locations when it is appropriate to do so.

The results also suggest that, across the evolution of vertebrate species, the primary site in the brain where the midbrain network acts to select visual information for attention has changed dramatically. In fish, amphibians and reptiles, the vast majority of visual information passes through the OT on its way to the forebrain, where stimuli are identified. In these species, the midbrain network selects and filters information in the OT itself. In birds, although the pathway through the OT is still the dominant visual pathway, the direct visual pathway to the forebrain (the retino-thalamic pathway) increases in size and importance. In mammals, and especially in primates, the retino-thalamic pathway is the dominant visual pathway to the forebrain. In these later-evolved species, the midbrain’s selection of visual information for attention acts more importantly on information that is being conveyed to the forebrain via the direct, retino-thalamic pathway.

Closing the Laboratory

My first thoughts of closing the laboratory arose indirectly from my difficulties in raising funds for the lab. Gradually, my students came to recognize that the entrenched resistance to funding research on “nonstandard” species was a serious obstacle to a successful career. In addition, my lack of reliable long-term funding hampered my ability to recruit new graduate students and postdocs. One day it dawned on me that I would have to make a choice: either change my research back to studies on neural mechanisms of learning in barn owls or close the lab. In 2015, at 65 years of age, I decided it was time to begin closing the lab, a process that proceeded gradually over the next several years.

Upon hearing this news, Dan Feldman, who had been a stellar graduate student in my lab and was now a professor at UC Berkeley, organized a reunion of colleagues who had worked with me during my years at Stanford. He scheduled a symposium, an evening banquet, and a luncheon for the following day. Most of the graduate students, postdocs, and faculty with whom I had worked closely attended. They came from far and wide. It was a wonderful event and, for me, an unforgettable experience.

Once Phyllis and I had finished analyzing the data from our final research project, Phyllis retired, and I continued to write up the results. After submitting this research paper for publication (Knudsen et al., 2017), I began working on a review paper that summarized all that we had learned over the previous 10 years about the circuits and mechanisms that mediate selective attention. This was important because the order in which we had done the experiments was backward to the traditional order: we had analyzed the neural circuits before we had demonstrated the contributions of the circuits to behavior. The review paper enabled me to present our work as a coherent story from behavior to cellular mechanisms and to place the work in the context of current knowledge about selective attention and how it works (Knudsen, 2018). Publishing this review gave me a sense of completion and closure to my research career. As I write this autobiography, I am an emeritus professor, with an office that commands a great view of the Santa Cruz Mountains, and I have free access to Stanford facilities and a permanent A-parking sticker!

Reflections

I was extremely lucky to have lived during a magical era in neuroscience. This era witnessed spectacular advances in our understanding of the brain as well as revolutionary changes in technologies and computational tools. Questions that were only posed as “thought experiments” one year, often became technically feasible just a few years later. Today, experiments are limited more by understanding and imagination than by technology. These are exciting times in neuroscience.

As is true of all careers, my career was profoundly affected by fortuitous events. For example: had Jim Case not been my undergraduate advisor at UCSB, I would have become a marine ecologist, and not a neuroscientist; had Mark Konishi not been a close friend of Walter Heiligenberg, I would not have studied barn owls as a postdoc; had Mark not been away on a trip on the day when Denis Baylor came to give a seminar at Caltech, I would not have been invited to interview for the assistant professorship at Stanford University. I was so lucky that these critical events, and many others, opened up the career path that I followed.

I was also fortunate to have been surrounded throughout my career by extremely bright colleagues and students. One of my greatest joys has been interacting with brilliant, creative people, developing ideas, and discovering scientific truths. It is these interactions and these people who deserve the credit for most of my accomplishments. This also applies to teaching. As mentioned previously, I do not enjoy public speaking. However, team-teaching together with gifted faculty has been extremely rewarding and, at many times, fun.

Lessons Learned

Always work on a “big question” that inspires you. Keeping this big question firmly in mind helps to guide your prioritization of experiments and provides you with the motivation necessary to persevere through the periods of tedium and experimental failure that are inherent to the scientific process.

Don’t be afraid to follow your changing interests. Expect your “big question” to evolve as your career unfolds. By noticing what you enjoy discussing at the water cooler and how you describe the importance of your research to friends and family, you will realize when your interests are changing. Follow your changing interests.

When selecting an experimental animal, consider the advantages afforded by nonstandard species. Millions of years of environmental challenges have selected for the elaboration of amazing behaviors and brain mechanisms in certain species. The elaboration of behaviors and mechanisms makes the exploration of the brain’s solutions to a “big question” easier, more informative, and more interesting in these species.

Do not be seduced easily by the latest new technologies. Just because new types of measurements can be made does not mean that they provide the best data for answering your question.

Maintain a balanced lifestyle. Interleave focused research with other activities that allow your mind to engage the world in completely different ways. Breakthrough ideas often arrive during such periods.

Cultivate a rich and diverse set of friends and collaborators. Although many discoveries come through careful thought and introspection, many others result from interactions with people of different backgrounds and points of view. Sharing and debating ideas with colleagues accelerates understanding, increases productivity, and makes science fun.

The Future

There is nothing that compares with the exhilaration that comes with “aha!” moments of scientific discovery: the realization of a truth that no one else, in the history of mankind, has recognized. In retirement, I miss those moments. I also miss the exhilaration of delivering a good seminar or of teaching bright students about new ideas or ways of thinking. However, I do not miss the many administrative duties attendant to being an active faculty member or the stresses of public speaking, especially as my flexibility of thought and reliability of memory decreases.

Although retired, I continue to immerse myself in science. I maintain an office at Stanford, where I read, write, and talk with brilliant people who are shaping the future of neuroscience. I also monitor the growth of my department and follow the progress of the next generation of outstanding faculty members, as they embark on exciting scientific careers.

With substantial unscheduled time at our disposal, Phyllis and I travel often, taking both planned and spur-of-the-moment trips. On a typical weekday, morning office time is followed by workouts in the gym, basketball, pickleball, or oil painting. Wednesday and Sunday mornings I keep open for surfing. Some days are devoted to projects in my community. Occasionally, I go fishing in the ocean for salmon and halibut or fly fishing in the mountains for trout. Finally, and most important, my family continues to be a major source of joy and happiness, as it evolves and differentiates in the unpredictable ways that families always do. Life is good. Carpe diem!

Selected Bibliography

Asadollahi A, Knudsen EI (2016) Spatially precise visual gain control mediated by a cholinergic circuit in the midbrain attention network. Nat Commun. 7: 13472.

Asadollahi A, Mysore SP, Knudsen EI (2010) Stimulus-driven competition in a cholinergic midbrain nucleus. Nat Neurosci. 13: 889–895.

Bergan JF, Ro P, Ro D, Knudsen EI (2005) Hunting increases adaptive auditory map plasticity in adult barn owls. J Neurosci. 25: 9816–20.

Brainard MS, Knudsen EI (1993) Experience-dependent plasticity in the inferior colliculus: a site for visual calibration of the neural representation of auditory space in the barn owl. J Neurosci. 13: 4589–608.

Brainard MS, Knudsen EI (1995) Dynamics of visually guided auditory plasticity in the optic tectum of the barn owl. J Neurophysiol. 73: 595–614.

Bryant AS, Goddard CA, Huguenard JR, Knudsen EI (2015) Cholinergic control of gamma power in the midbrain spatial attention network. J Neurosci. 35: 761–75.

Cohen YE, Knudsen EI (1995) Binaural tuning of auditory units in the forebrain archistriatal gaze fields of the barn owl: local-organization but no space map. J Neurosci. 15: 5152–68.

Cohen YE, Knudsen EI (1999) Maps versus clusters: different representations of auditory space in the midbrain and forebrain. Trends Neurosci. 22: 128–35.

Cohen YE, Miller GL, Knudsen EI (1998) Forebrain pathway for auditory space processing in the barn owl. J Neurophysiol. 79: 891–902.

DeBello WM, Knudsen EI (2004) Multiple sites of adaptive plasticity in the owl’s auditory localization pathway. J Neurosci. 24: 6853–61.

DeBello WM, Feldman DE, Knudsen EI (2001) Adaptive axonal remodeling in the midbrain auditory space map. J Neurosci. 21: 3161–74.

du Lac S, Knudsen EI (1990) Neural maps of head movement vector and speed in the optic tectum of the barn owl. J Neurophysiol. 63: 131–46.

du Lac S, Knudsen EI (1991) Early visual deprivation results in a degraded motor map in the optic tectum of barn owls. Proc Natl Acad Sci USA. 88: 3426–30.

Feldman DE, Knudsen EI (1997) An anatomical basis for visual calibration of the auditory space map in the barn owl’s midbrain. J Neurosci. 17: 6820–37.

Feldman DE, Knudsen EI (1998) Pharmacological specialization of learned auditory responses in the inferior colliculus of the barn owl. J Neurosci. 18: 3073–87.

Goddard CA, Sridharan D, Huguenard JR, Knudsen EI (2012) Gamma oscillations are generated locally in an attention-related midbrain network. Neuron. 73: 567–80.

Goddard CA, Mysore SP, Bryant AS, Huguenard JR, Knudsen EI (2014) Spatially reciprocal inhibition of inhibition within a stimulus selection network in the avian midbrain. PLoS One. 9: e85865.

Gold JI, Knudsen EI (2000a) Abnormal auditory experience induces frequency-specific adjustments in unit tuning for binaural localization cues in the optic tectum of juvenile owls. J Neurosci. 20: 862–77.

Gold JI, Knudsen EI (2000b) A site of auditory experience-dependent plasticity in the neural representation of auditory space in the barn owl’s inferior colliculus. J Neurosci. 20: 3469–86.

Gutfreund Y, Knudsen EI (2006) Adaptation in the auditory space map of the barn owl. J Neurophysiol. 96: 813–25.

Gutfreund Y, Zheng W, Knudsen EI (2002) Gated visual input to the central auditory system. Science. 297: 1556–59.

Hyde PS, Knudsen EI (2000) Topographic projection from the optic tectum to the auditory space map in the inferior colliculus of the barn owl. J Comp Neurol. 421: 146–60.

Hyde PS, Knudsen EI (2002) The optic tectum controls visually guided adaptive plasticity in the owl’s auditory space map. Nature. 415: 73–76.

Knudsen EI (1973) Muscular activity underlying ventilation and swimming in the horseshoe crab, Limulus polyphemus (Linnaeus). Biol Bull. 144: 355–67.

Knudsen EI (1974) Behavioral thresholds to electric signals in high-frequency electric fish. J Comp Neurol. 91: 333–53.

Knudsen EI (1975a) Centralgenic motoneuron bursts accompanying various gill plate movements in Limulus polyphemus (Linnaeus). Comp Biochem Physiol A Comp Physiol. 51: 465–69.

Knudsen EI (1975b) Spatial aspects of electric-fields generated by weakly electric fish. J Comp Neurol. 99: 103–18.

Knudsen EI (1976) Midbrain responses to electroreceptive input in catfish—evidence of orientation preferences and somatotopic organization. J Comp Neurol. 106: 51–67.

Knudsen EI (1978) Functional organization in electroreceptive midbrain of catfish. J Comp Neurol. 41: 350–64.

Knudsen EI (1982) Auditory and visual maps of space in the optic tectum of the owl. J Neurosci. 2: 1177–94.

Knudsen EI (1985) Experience alters the spatial tuning of auditory units in the optic tectum during a sensitive period in the barn owl. J Neurosci. 5: 3094–109.

Knudsen EI (2004) Sensitive periods in the development of the brain and behavior. J Cogn Neurosci. 16: 1412–25.

Knudsen EI (2007) Fundamental components of attention. Annu Rev Neurosci. 30: 57–78.

Knudsen EI (2011) Control from below: the role of a midbrain network in spatial attention. Eur J Neurosci. 33: 1961–72.

Knudsen EI (2012) Midbrain and forebrain systems for bottom-up control of spatial attention. In: The Neuroscience of Attention: Attentional Control and Selection (Mangun GR, ed.), pp. 131–50. New York: Oxford University Press.

Knudsen EI (2018) Neural circuits that mediate selective attention: a comparative perspective. Trends Neurosci. 41: 789–805.

Knudsen EI, Konishi M (1978a) Space and frequency are represented separately in auditory midbrain of owl. J Neurophysiol. 41: 870–84.

Knudsen EI, Konishi M (1978b) A neural map of auditory space in the owl. Science. 200: 795–97.

Knudsen EI, Konishi M (1979) Mechanisms of sound localization in the barn owl (Tyto-Alba). J. Comp. Physiol 133: 13–21.

Knudsen EI, Knudsen PF (1985) Vision guides the adjustment of auditory localization in young barn owls. Science. 230: 545–48.

Knudsen EI, Knudsen PF (1989) Vision calibrates sound localization in developing barn owls. J Neurosci. 9: 3306–13.

Knudsen EI, Schwarz JS (2017) The optic tectum: a structure evolved for stimulus selection. In: Evolution of the Nervous System, 2nd edition (Kaas JH, ed.), pp. 387–408. New York: Elsevier.

Knudsen EI, Konishi M, Pettigrew JD (1977) Receptive-fields of auditory neurons in owl. Science. 198: 1278–80.

Knudsen EI, Blasdel GG, Konishi M (1979) Sound localization by the barn owl measured with the search coil technique. J Comp Physiol. 133: 1–11.

Knudsen EI, Knudsen PF, Esterly SD (1982) Early auditory experience modifies sound localization in barn owls. Nature. 295: 238–40.

Knudsen EI, Esterly SD, Knudsen PF (1984a) Monaural occlusion alters sound localization during a sensitive period in the barn owl. J Neurosci. 4: 1001–11.

Knudsen EI, Knudsen PF, Esterly SD (1984b) A critical period for the recovery of sound localization accuracy following monaural occlusion in the barn owl. J Neurosci. 4: 1012–20.

Knudsen EI, Esterly SD, du Lac S (1991) Stretched and upside-down maps of auditory space in the optic tectum of blind-reared owls; acoustic basis and behavioral correlates. J Neurosci. 11: 1727–47.

Knudsen EI, Cohen YE, Masino T (1995) Characterization of a forebrain gaze field in the archistriatum of the barn owl: microstimulation and anatomical connections. J Neurosci. 15: 5139–51.

Knudsen EI, Heckman JJ, Cameron JL, Shonkoff JP (2006) Economic, neurobiological, and behavioral perspectives on building America’s future workforce. Proc Natl Acad Sci USA. 103: 10155–62.

Knudsen EI, Schwarz JS, Knudsen PF, Sridharan D (2017) Space-specific deficits in visual orientation discrimination caused by lesions in the midbrain stimulus selection network. Curr Biol. 27: 2053–64, e2055.

Konishi M, Knudsen EI (1979) The oilbird: hearing and echolocation. Science. 204: 425–27.

Linkenhoker BA, Knudsen EI (2002) Incremental training increases the plasticity of the auditory space map in adult barn owls. Nature. 419: 293–96.

Linkenhoker BA, von der Ohe CG, Knudsen EI (2005) Anatomical traces of juvenile learning in the auditory system of adult barn owls. Nat Neurosci. 8: 93–98.

Maczko KA, Knudsen PF, Knudsen EI (2006) Auditory and visual space maps in the cholinergic nucleus isthmi pars parvocellularis of the barn owl. J Neurosci. 26: 12799–806.

Masino T, Knudsen EI (1990) Horizontal and vertical components of head movement are controlled by distinct neural circuits in the barn owl. Nature. 345: 434–37.

Middlebrooks JC, Knudsen EI (1984) A neural code for auditory space in the cat’s superior colliculus. J Neurosci. 4: 2621–34.

Middlebrooks JC, Knudsen EI (1987) Changes in external ear position modify the spatial tuning of auditory units in the cat’s superior colliculus. J Neurophysiol. 57: 672–87.

Miller GL, Knudsen EI (2003) Adaptive plasticity in the auditory thalamus of juvenile barn owls. J Neurosci. 23: 1059–65.

Mogdans J, Knudsen EI (1994) Site of auditory plasticity in the brain stem (VLVp) of the owl revealed by early monaural occlusion. J Neurophysiol. 72: 2875–91.

Mysore SP, Knudsen EI (2012) Reciprocal inhibition of inhibition: a circuit motif for flexible categorization in stimulus selection. Neuron. 73: 193–205.

Mysore SP, Knudsen EI (2013) A shared inhibitory circuit for both exogenous and endogenous control of stimulus selection. Nat Neurosci. 16: 473–78.

Mysore SP, Knudsen EI (2014) Descending control of neural bias and selectivity in a spatial attention network: rules and mechanisms. Neuron. 84: 214–26.

Olsen JF, Knudsen EI, Esterly SD (1989) Neural maps of interaural time and intensity differences in the optic tectum of the barn owl. J Neurosci. 9: 2591–605.

Sridharan D, Boahen K, Knudsen EI (2011) Space coding by gamma oscillations in the barn owl optic tectum. J Neurophysiol. 105: 2005–17.

Sridharan D, Steinmetz NA, Moore T, Knudsen EI (2014a) Distinguishing bias from sensitivity effects in multialternative detection tasks. J Vis. 14.

Sridharan D, Ramamurthy DL, Schwarz JS, Knudsen EI (2014b) Visuospatial selective attention in chickens. Proc Natl Acad Sci USA. 111: E2056–65.

Sridharan D, Steinmetz NA, Moore T, Knudsen EI (2017) Does the superior colliculus control perceptual sensitivity or choice bias during attention? Evidence from a multialternative decision framework. J Neurosci. 37: 480–511.

Winkowski DE, Knudsen EI (2006) Top-down gain control of the auditory space map by gaze control circuitry in the barn owl. Nature. 439: 336–39.

Winkowski DE, Knudsen EI (2007) Top-down control of multimodal sensitivity in the barn owl optic tectum. J Neurosci. 27: 13279–91.

Winkowski DE, Knudsen EI (2008) Distinct mechanisms for top-down control of neural gain and sensitivity in the owl optic tectum. Neuron. 60: 698–708.

Witten IB, Bergan JF, Knudsen EI (2006) Dynamic shifts in the owl’s auditory space map predict moving sound location. Nat Neurosci. 9: 1439–45.

Witten IB, Knudsen EI, Sompolinsky H (2008) A Hebbian learning rule mediates asymmetric plasticity in aligning sensory representations. J Neurophysiol. 100: 1067–79.

Zheng GL, Knudsen EI (1999) Functional selection of adaptive auditory space map by GABA-mediated inhibition. Science. 284: 962–65.

Pierre J. Magistretti

BORN:

Milano, Italy

September 30, 1952

EDUCATION:

University of Geneva Medical School, Diploma (1977)

University of Geneva Medical School, Doctorate (1979)

University of California at San Diego, PhD (1982)

APPOINTMENTS:

Maître Assistant, Department of Pharmacology, University of Geneva (1982–1987)

Professor, Department of Physiology, University of Lausanne Medical School (1988–2004)

Chairman, Department of Physiology, University of Lausanne Medical School (2001–2004)

Director, Brain Mind Institute, EPFL (2008–2012), Co-Director (2005–2008)

Founding Director, Center for Psychiatric Neuroscience, University of Lausanne (2004–2012)

Director, National Center for Competence SynaPsy (2010–2016)

Distinguished Professor and Dean, KAUST (2012–)

Professor Emeritus, EPFL (2017), University of Geneva (2017), University of Lausanne (2018)

HONORS AND AWARDS (SELECTED)

President, Swiss Society for Neuroscience (1997–1999)

President, Federation of European Neuroscience Societies (FESN) (2002–2004)

President, International Brain Research Organization (IBRO) (2014–2019)

Member: Board of Trustees, Human Frontier Science Program (2003–2018)

Vice Chairman, European Dana Alliance for the Brain (EDAB) (2002–)

IPSEN Foundation Prize, Co-recipient with David Attwell and Marcus Raichle (2016)

Honorary member of the Chinese Association for Physiological Sciences (2014)

Camillo Golgi Medal Award, Golgi Foundation (2011)

Goethe Award for Psychoanalytic Scholarship, Canadian Psychological Association (2009)

International Chair Professor, Collège de France (2007–2008)

Emil Kraepelin Guest Professorship, Max Planck Institute für Psychiatrie (2002)

Member of the Swiss Academy of Medical Sciences, ad personam (2001)

Member of Academia Europaea (2001)

Pierre Magistretti has made important contributions to the study of brain energy metabolism and has pioneered the field of glia biology. His laboratory has discovered some of the cellular and molecular mechanisms that underlie the coupling between neuronal activity and energy consumption by revealing the key role that glial cells, in particular astrocytes, play in this physiological process. Pierre Magistretti has unraveled the role of lactate produced by astrocytes through the Astrocyte Neuron Lactate Shuttle not only as an energy substrate for neurons but also as a signaling molecule in the brain. These findings are particularly relevant for understanding the origin of the signals detected by functional brain imaging and have revealed the role of astrocytes and lactate in neuronal plasticity, memory and neuroprotection. Over the past decade, he has engaged in translational research in psychiatry focusing on the role of glia in psychiatric diseases.

Pierre J. Magistretti

I was surprised and honored to receive the request by Tom Albright and Larry Squire asking me to contribute a chapter for the Society for Neuroscience series History of Neuroscience in Autobiography. Over the preceding 20 years, I had made cursory readings of some of the chapters written by neuroscientists I knew. Two things had struck me: first, the personal side of the narrative and, second, the path to their original observations and successful careers, including the scientific aspects and also, and maybe more so, the personal choices and anecdotes that guided them. In fact, I am not certain that the term “guided” is the appropriate one: indeed, when one reads a biography, life events often appear to the reader as representing an orderly sequence of logical steps based on mostly rational decisions. Granted, an unexpected event may pepper here and there the narrative and be given appropriate importance in determining life’s course, but the logical sequence stands strong. The evolutionary value of such mental process is obvious, in that our brains are geared to make predictions that guide decisions ensuring survival. This process, however, also may intrude when one looks back into one’s past life. One tends to remember life events mostly as following a master plan, even when the unexpected occurred. A friend psychoanalyst with a great sense of humor once told me that psychoanalysts tend to be great specialists in making predictions of the past! It is the challenge of the narrator to capture the unpredictability of life and the infinite opportunities that it had offered in the course of one’s existence.

Early Years in Milano

I was born in Milano, Italy, on September 30, 1952, to two young doctors: Massimiliano, known as Max, Magistretti and Carla Giuliana, known as Liana, née Bolis. They had met during medical school in Milano, my mother Liana being one of five women out of a class of 80 or so. Things have fortunately changed since then. My father Max was the second son of a successful architect, Pier Giulio Magistretti, who had designed among other important buildings in Milano, the Arengario,¹ an edifice tainted by the grandiosity of the architectural style current in Italy in the 1920s and 1930s, which sits next to the Duomo, the magnificent Gothic cathedral. It hosts now a very interesting museum featuring Italian art of the 20th century. I remember the outings with my grandmother from my mother’s side, Francine, and one of her daughters who lived with her, my beloved Aunt Giovanna, to the Duomo square to feed the pigeons and the inevitable comments, mostly negative, they made about Pier Giulio’s building. This obviously biased for a long time my appreciation of the building, but I now find it nice and harmoniously fitting the large Duomo square. One should appreciate the challenge that my grandfather faced: to design a building that could sit next to a cathedral built five centuries earlier.

My father had an older brother, Vico, who followed his father’s path, becoming one of the great Italian architects and designers of the 20th century (Pasca, 1991; Irace and Pasca, 1999). He was one of the founding fathers of the cultural movement that was born in Milano after World War II and made the city one of the capitals of design. Several of his pieces are displayed in design museums, including the MOMA. He died in 2006. A street has been recently named after him in Milano and in 2020 a large retrospective takes place at the Triennale museum in Milano to celebrate his centennial. Still now, I am asked, mostly in Europe, if I am related to Vico Magistretti. This is fine with me, but I know that it was something that tended to bother my dad when he was asked. He had somehow suffered being in the shadow of his older brother during his short life. My father died at age 48 while on vacation in the Eolian Islands.

Vico and Max had a younger sister, Luisa, a child psychologist who married a surgeon, Sergio Pliteri, who specialized in abdominal surgery. When I was eight, he operated on me for an appendicitis. He published two books: one about his life experience as a surgeon and another on his specialty, exocrine pancreas surgery (Pliteri 2003; Pliteri and Sironi 2005).

My mother was from a larger family: she had five siblings born to Pietro Bolis, an engineer who specialized in the design and construction of hydroelectric power plants, and Françine, née Grassi, a housewife. My grandmother brought some French heritage, as she was born near Nice in the South of France close to the Italian border. I keep very fond memories of my grandmother Françine as I spent a good part of my childhood years, between three and nine, with her in her apartment in Milano or, during the summers, in Sospel a small village near Nice where she kept the house where she was born. My mother was very busy with her professional life, and she would drop me with grandma Françine for entire days; sometimes I even stayed for sleepovers. Her love and attention for me have been a priceless gift: she told me stories of her family and she taught me geography, which I loved. We would spend time in the kitchen watching the maid cook, as I was eager to learn and “help.” I still love cooking, an activity that I think is akin to biochemistry, which eventually became my trade. I think I owe much to the unlimited love that my grandmother gave me, including the strength and serenity that helped me go through some difficult periods in my life. Two of my mother’s sisters married Frenchmen and lived in France. The summers in Sospel gave me the opportunity to see my French cousins and to become fluent in French.

Soon after I was born, my parents moved to a small village in the Alps, North of Milano, known as Sondalo, where my father was hired as a resident in a sanatorium. This type of hospital, which is usually located in sunny places where the air is pristine, had become popular for the management of patients with tuberculosis, before the advent of antibiotics. In fact, my father had spent several months during medical school as a patient in that very sanatorium. My mother worked there in the laboratory medicine unit running blood tests of the patients. I have no recollection of the year I spent there: my mother later told me that it had been the happiest year in her married life.

After one year as a resident, my father became interested in cardiology and obtained a fellowship to enroll in a program at the University of Brussels. My mother adjusted to this novel situation and managed to obtain another fellowship, in the Department of Physiology in the same university. Her research project was about the emerging field of transport of ions and solutes across cell membranes, in particular red blood cells, a topic that she would pursue over the next 50 years.

In the fall of 1955, we came back to Milano where my father joined the Department of Cardiology as a senior clinical fellow with the intent to pursue an academic career. He was in fact following one of the family traditions, clinical medicine (the other one being architecture) that dated back to the 18th century. Indeed, the Magistretti emigrated to Milano from Torricella, a small village near Lugano in the Italian-speaking part of Switzerland, in the mid-1700s (Locatelli, 2012). Over the following 200 years, several Magistretti engaged in the medical profession. The most prominent physician of my family was probably Pietro Magistretti (Figure 1), who enrolled in 1786 in the faculty of medicine at the University of Pavia. He was trained by the then-famous surgeon Antonio Scarpa, who found talent in the young Magistretti and sent him in 1790 to Vienna, for further training in ophthalmology with Joseph Barth (Giulietti, 2008). Pietro Magistretti had a distinguished career as a professor of anatomy and an ophthalmologist in Milano during the 19th century, his claim for fame being to have successfully operated, in 1811, on the eye of the prominent Italian literate, Ugo Foscolo (Giulietti, 2008). A small street is named after Pietro Magistretti in Milano.

Fig. 1. Portrait of Pietro Magistretti, Professor of Anatomy and distinguished ophthalmologist. Circa 1810, by Luigi Sabatelli.

While my father was pursuing his academic career, which however did not bring great revenues, my mother took a well-remunerated job as scientific director of a small pharmaceutical company in Milano that belonged to the father of one of her childhood friends. Her job ensured a good financial situation that even improved the following year. We then moved from the small apartment we had been renting upon our return from Brussels into a nice and large apartment that my father inherited. The apartment was located in a building in the center of Milano, Via Conservatorio 20, that grandfather Pier Giulio had designed. The whole Magistretti “clan” lived there: Uncle Vico and Aunt Luisa with their family, grandmother Cina (her husband Pier Giulio had died at the end of the war) and now Max with his family, which had welcomed a new arrival: Filippo, born in July 1956. Other apartments had been sold or rented to a few tenants. The offices of my grandfather’s firm were now occupied by Vico. Since the demise of Vico in 2006, the offices are now home to a foundation, where the works of Vico are on display.²

The building faced a square surrounded on the other three sides by the baroque church Santa Maria della Passione, the Verdi music conservatory, and Palazzo Archinto, a 19th-century building, home of a private school for girls, which had been designed by my great-great grandfather, the architect Gaetano Besia. I would spend long afternoons playing football (soccer) with my older cousin Stefano and friends in the square facing our building and the church, to the great displeasure of the priests. I remember as a torture being called in from the balcony of my apartment to stop immediately playing football and run home for my piano lesson.

I soon joined a public primary school nearby, Scuola Corridoni: we had to wear a black overall with a white collar and a large blue tuft, an outfit I found quite unaesthetic. I was a disciplined pupil pleasing my teachers and parents and receiving good marks. When I reached fourth grade in 1961, Italy celebrated the centennial of its reunification. Until 1861, several independent states had occupied the Italian Peninsula, not the least the Vatican State in the center. Giuseppe Garibaldi conquered Sicily and the Southern part of Italy and handed them to King Victor Emmanuel II of Savoy, who eventually became the first King of Italy. Thus, 1961 was a year of patriotic enthusiasm: we learned the names of all the battles and heroes that contributed to the reunification. Now, almost six decades after I left Italy, I still feel deep inside myself a patriotic fiber, in particular when the Italian football team wins a match.

Life continued uneventfully until 1963. A quiet and protected life of a boy from the Milanese bourgeoise: first Communion after several months of instruction by the priests of Santa Maria della Passione, frequent weekend outings with my parents to Lake Como and Lake Maggiore, skiing in Courmayeur during winter, football matches at San Siro stadium with my father to watch Inter—the favored team of the Magistretti—summers at my grandmother’s place in Sospel. In August 1963, I received a call from my mother while my brother and I were staying with one of our French aunts. I will never forget that conversation: it meant the end of the world, at least of my world. My mother announced to me that our parents were getting separated and that we would be sent to a boarding school in the Swiss Alps. She said that it would be best for us to be removed from the turmoil of the new family situation. I was asked to explain this to my younger brother. I had noticed during the preceding months that my mother looked sad, occasionally I caught her crying; my father was less present, and I had registered some hints that our lifestyle might change for the upcoming new school year, but I couldn’t see the catastrophe that was to come.

The Unexpected Move to Switzerland

On September 19, 1963, we arrived in Crans-Montana, a tourist resort in the French speaking region of Switzerland, which was rather popular with Milanese families since by train it was only a few hours away from the city. My mother accompanied us with the intent to spend a couple of months to recover from what was most likely a breakdown. A great aunt from my father’s side joined for a week to help us settle. We arrived on a Thursday: Monday morning I was sitting in a fifth-grade classroom, with people I had never met who spoke only French. Actually I had no problem to communicate with them, but I was completely incompetent in writing as, unlike Italian, written French is not phonetic and its orthography rules are rather challenging. For my first dictation, I made almost as many errors as there were words. My mother had insisted that I join secondary school, as I had completed my elementary studies in Milano. The director of the school argued that the change in language and culture would be challenging enough and that secondary school would be above my competencies. Despite my weaknesses in writing, it soon became clear that my level of knowledge was above that of my classmates and that I should join the first year of secondary school. There, I definitely found many challenges, as it was my first exposure to several branches of knowledge: Latin, German, English, algebra, French literature (all taught in French, of course). My father had insisted that we attended a public school, as he considered that international private boarding schools were academically insufficient. So, once my mother left in early January 1964, my brother and I were placed in a boarding school for food and lodging, but were attending the local public school.

The first few months were destabilizing. While academically I caught up relatively quickly, I missed my family life; the cultural and social environment presented new challenges every day, with the local classmates and teachers on one side and the international crowd of the boarding school on the other. I had to constantly adapt: fortunately, I had my brother Philippe, as he was now being called, the only reference point I had from my previous life. The bond we created helped us go through these difficult times and still persists strongly today. Like my brother, I also converted my Italian first name, Pier Giulio (my grandfather’s name), into its French and shorter version, Pierre. We felt that by changing our names, we were helping our integration. My classmates were mostly born in 1949 or 1950: two to three years at that age make a big difference. The boys were strong, most of them sports oriented and not particularly motivated academically; the girls were naturally more mature and were proficient. I was struggling physically, in fact once while playing rough, two of my buddies threw me into a ravine breaking my leg. Discipline was strictly enforced by the teachers: being grounded for peccadilloes was the rule; physical punishments (hands hit with a wooden stick) were not rare. Quite a change from my pampered life in Milano! My safe place was learning: I was performing well in school, had good marks, and was able to achieve some sort of consideration from my classmates. By the third year in secondary school, I had physically grown and was able to follow down the ski slopes the “big guys” in the class.

Despite what had undoubtedly been a hardship, I am very fond of those years in Crans-Montana. It was a life-changing experience that influenced the ways I have approached new situations later in life. I learned to adapt, to understand other cultural backgrounds, and to organize my work to achieve a goal, and probably most of all, it has given me an assurance that with persistence one finds light at the end of a tunnel. Fifty-six years since I first landed in Crans-Montana, I still regularly spend time there, where we have an apartment. I am friends with many former classmates who now work in or own hotels, restaurants, bakeries, sports stores, real estate companies, or garages. Crans-Montana brought me another gift that has had some importance in my life: golf. Indeed, Crans-Montana is the site a magnificent 27-hole course where the Swiss Open has been played since the 1930s. Over the past decade, the Swiss Open has become the European Masters, at which world class professionals compete. Golf and Crans-Montana are synonymous: every local plays or is somehow involved in golf. It is a small Scottish oasis in the middle of the Alps. I started playing golf just before the first snowflakes began to fall in the winter of 1963. Over the years, I became quite good, reaching a handicap of one and eventually playing for the Swiss National team during the better part of the 1970s.

Upon her return to Milano in January 1964, after the convalescence period in Crans-Montana, my mother decided to try an academic career. Not an easy decision for a forty-year-old woman. She reconnected with colleagues in the Department of Pharmacology at the University of Milano, where she had done some internships during medical school and managed to obtain a part-time fellowship to work on transport properties of red blood cell membranes. She also kept some consultancies in the pharmaceutical industry. These activities kept her quite busy, while she was also trying to rebuild a personal life. We would not see her much during those years, nor our father for that matter.

The Roman Experience

In 1966, my mother obtained the equivalent of an assistant professorship at the University of Rome, in the Department of General Physiology. The decision was made for us to join her in Rome and enroll in school there. My father was a bit hesitant about us living in the capital. As a man from the North of Italy he was wary about the Roman lifestyle: he felt that the Roman “Dolce vita” would not be conducive for serious academic studies. We moved into a small apartment in a calm residential area near Villa Borghese, with a nice garden and many trees around the building. Now back to Italian, I enrolled in a curriculum of classical studies with the main emphasis on Latin, ancient Greek, philosophy, history, and Italian literature. French was my foreign language (I got a break there); science teaching was on the light side. I realize now what a privilege it was to study classics in Rome: the heritage of the ancient Romans is before one’s eyes. You read a speech by Cicero one day and you can visit the next day where he pronounced it two millennia earlier. But thanks to an exceptional teacher, my passion soon became studying ancient Greek literature. I was in particular, fascinated by the ancient Greek lyric poets. They were active between 600 and 300 B.C. and described the depth of human emotions so vividly, in a timeless manner that makes them very contemporary. Here is a poem about love, written more than 2,500 years ago by the lyric poet Sappho (D’Angour, 2013):

He seems to me, that man, almost a god—

the man, who is face to face with you,

sitting close enough to you to hear

your sweet whispering

And your laughter, glistening, which

the heart in my breast beats for.

For when on you I glance, I do not,

not one sound, emit.

But my tongue snaps, lightly

runs beneath my flesh a flame,

and from my eyes no light, and rumbling

comes into my ears,

And my skin grows damp, and trembling

all over racks me, and greener than the grass

am I, and one step short of dying

I seem to myself.

The fact that those poems and other productions of ancient Greek literature were placing human sentiments at center stage in ways that were still moving readers in the 20th century gave me the first hint that there may be some sort of universality of emotions and feelings that transcended cultures, times, and geographic locations. This intuition was reinforced by readings that were rather en vogue at the time, including those of structuralists such as Claude Lévi-Strauss and Roland Barthes, which emphasized the existence of constant laws of abstract structure for how humans perceive, analyze, and organize systems, such as natural and social environments, as well as how they develop systems like language. My possibly naïve and certainly simplistic take from these readings was that there must be a biological basis for these mental processes and that to understand the human mind, I should study the brain. Several years later, I was telling my brother that this was how I thought I decided to become a neuroscientist. He argued instead, with his dry sense of humor, that I chose this path because I realized that our parents were emotionally unstable and I decided to try and understand them by studying the organ of behavior.

The late 1960s were years of social unrest in Europe, sparked by the student revolts of May 1968 in Paris. Rome, like many other cities, followed: our school was regularly occupied by the students. We would debate for hours about political issues, challenging the capitalistic and patriarchal organization of society, down to what was thought to by its most dysfunctional unit: the family. These were intellectually stimulating times, but clearly quite disruptive for the academic curriculum. Likewise, universities were often closed because of violent confrontations between the students and police. I had two years left before graduating from high school and entering university. (In Europe, the high school curriculum is eight years, the last two being equivalent to the first two years of college in the United States.) It was pretty clear that studying in Italy during the next couple of years would be disrupted. I was torn between the attraction that I had for the political and social issues that were debated, and my determination to move ahead with my studies. I was hesitating between psychology, biology, and at some point even architecture with the idealistic view to build cities for a more just society. My parents were telling me, as they later told my brother: “study medicine, then you can chose what you really want.” By default, I eventually decided that I would enroll in medical school. Given the unstable situation in Italian universities, I thought that returning to Switzerland was the way to go. The problem, however, was that one needed a Swiss high school diploma to enroll in a Swiss medical school.

The solution was to take, as a private student, an exam called Maturité Fédérale, which is administered twice a year in select academic venues in one of the three linguistic regions of Switzerland. I checked the requirements for the exam in the Italian-speaking Ticino region. I concluded that, in view of the strong training I had received in Rome in classics, the relative ease with which I was handling the scientific subjects, and the fact that French would be my foreign language, I should have no problem passing that exam when I graduated from high school two years later. As I was thinking about this solution, I considered that spending two more years in Rome while being subjected to a bumpy academic curriculum was a loss of time. I could take the Swiss Maturité Fédérale exam within a year! I would retire from school, study alone at home, and take the exam the next summer session. Looking back on this decision now seems to me completely crazy. I was taking a monumental risk for an uncertain future. My father thought that it was a good idea; he had done the same thing during the war.

I moved back to Crans-Montana in September 1969, as I thought it would be impossible to focus on my studies in Rome. I prepared a weekly plan of work for the ten or so branches of knowledge on which I would be examined nine months later. That program required on my part a very strong discipline: I had received from the examination authority the textbooks that I should complete, and was moving along one chapter after the other, week after week. I arranged some tutoring in math, because this was, and still is, a weak point. I think that being back in Crans-Montana where I had studied a few years earlier in a disciplinarian school somehow put me in the right frame of mind for the challenge I had put on myself. Fortunately, during those months, I was living with a very nice and warm family, the Rey-Barras. Angèle, the mother, ran a small, family-style boarding school. She radiated an incredible positive energy that I found very reassuring. I became very attached to her, and in fact I consider her as my second mother. In July 1970, I successfully passed the Maturité Fédérale exam in Locarno, Ticino; I had my passport to the University of Geneva Medical School, where I had decided to enroll. Three years later, my brother Philippe followed exactly the same path.

Medical School in Geneva

Those months of self-imposed hardship spent preparing for the Maturité Fédérale exam took a toll on me. I had some bouts of anxiety and felt emotionally and physically drained. My reaction to this condition was, I think, a healthy one: I played a lot of golf. My handicap went down dramatically, reaching two by the end of the summer. The lazy mood persisted through the fall of 1970: I was spending time in Rome catching up with my friends and hardly went to class in Geneva. Early December, I eventually moved to Geneva into a small studio in the Old Town. My main motivation had been that Geneva was close to Crans-Montana, and it would be easier to spend the Christmas vacation there, where a French girl I had met during the summer, and of whom I was fond, would be. During the second part of the academic year, I was more assiduous in attending lectures and labs. The program mostly consisted of physics, chemistry, and biology, all branches I had no major problem with. I passed the whole series of propedeutical exams, as they are called, and was ready to enter the second year when the “real stuff” would start: anatomy, histology, physiology, and biochemistry.

Biochemistry and physiology of the nervous system were my favorite subjects: I remember the excitement at the beginning of lectures, realizing that by the end of that day, I would know something new about those two topics. As the end of the second academic year was approaching, I arranged to spend the summer of 1972 at Duke University. I had a connection there, Daniel Tosteson, the chair of the Department of Physiology. My mother knew him through their common research interest in red blood cell membrane transport. A few years later, he became dean of Harvard Medical School, where he pioneered problem-based learning in the teaching curriculum. Dan was in fact much more than a professional acquaintance of my mother: he had become a close family friend and was very attentive to the academic and personal development of myself and my brother. He accepted very positively my request of spending a summer internship in his department. I learned there some theoretical biophysics of ionic transport and did experiments on transport across artificial membranes and red blood cells, some of which were carried out at the Marine Station in Beaufort, where Duke University had a laboratory. Most important, my summer internship at Duke represented a full immersion into the “American way of life,” including the culture and social life of a university campus. I also realized how political bipartisanism could exist in the same country or state, a consideration that is particularly relevant to today’s political landscape. For example, during the 1972 U.S. presidential race between McGovern and Nixon, the progressive, antiwar, and socially driven platform of the South Dakota senator was largely supported by the students and the academic personnel. Yet, when I left Duke’s campus and drove from Durham to Beaufort, I could read on a billboard on the side of the state highway a welcome message from the local Ku Klux Klan.

Thanks to my mother, Dan Tosteson was not the only prominent scientist whom I had the privilege to become acquainted with over the years. Soon after she started her appointment at the University of Rome, she set out to organize what she called “The international conference on biological membranes.” The field was burgeoning; she had a knack for convincing leaders in the field to attend and she established an atmosphere of camaraderie among them. Her biennial conferences took place in beautiful spots in Italy, and became a sort of salon, where high-quality science was presented and discussed in a relaxed atmosphere, with excellent Italian meals between the sessions. The proceedings of the conferences were published shortly after (e.g., see Karnovsky and Bolis, 1982). Attendance was limited to at most 40 participants. This is how I got to know Joseph Hoffmann, like Tosteson, a leader in red blood cell physiology; David Robertson, a pioneer of electron microscopy who developed the concept of the “unit membrane”; Richard Keynes, a major figure of the distinguished school of electrophysiology at Cambridge; and the Nobel Laureates Carl Cori, Feodor Lynen, Konrad Bloch, Carleton Gajdusek, Julius Axelrod, and Torsten Wiesel. I still have regular email exchanges with Torsten, and my wife and I occasionally have dinner with Torsten and his wife Mu. Over the years, I have often relied on Torsten’s wisdom for advice and guidance.

During my third year of medical school I enrolled in a new optional lab course called “Introduction to Medical Research” given by a recently appointed professor at the University of Geneva Medical School, Bernard Jeanrenaud, who was developing research projects in what we would call today “translational endocrinology.” His focus was on diabetes and his course was mostly hands on. The first experiment I did was to measure the activity of glycolytic enzymes in adipose tissue. Looking back to that year I spent working after hours and on weekends in his lab, I realize that in an amusing turn of fate (is it really fate?), the identification of glycolysis in astrocytes, as a main mechanism of metabolic cooperation between neurons and glial cells, has been one of the main research lines in my lab since the early 1980s.

Moving into the clinical years of medical school, my attraction for the study of the nervous system became even stronger, as I was following the lectures and bedside tutorials in neurology and psychiatry. As part of the required clinical internships, I spent several months in these two clinical services.

During the first months of 1977, with my colleagues, I was taking almost fortnightly an exam in clinical medicine branches, as part of what was called “Examen Final.” One week dermatology, two weeks later ophthalmology, followed by neurology, and so on for five months. This was a sort of marathon during which you review a given specialty, forget everything the moment you took the exam and switch to the next review. Prior to starting the Examen Final, I had arranged a position in the Department of Pharmacology at the University of Geneva Medical School, to work upon graduation with a junior faculty who had recently joined the department, Michel Schorderet. He had completed postdoctoral training in Paul Greengard’s lab at Yale, contributing to the demonstration that synaptic transmission in the superior cervical ganglion is associated with increases in cyclic adenosine 3′,5′-monophosphate (cAMP) in postsynaptic neurons (McAfee et al., 1971). As he did for the other few students who had enrolled in his course, Bernard Jeanrenaud facilitated my acceptance into a lab that would take medical graduates for experimental thesis work.

The Examen Final was successfully passed and I was ready, and very excited, to work in the lab for real. In fact, I had enjoyed working in the clinical services: I liked the contact with patients in all disciplines where I did an internship, with a fascination for obstetrics, since to see the birth of a new life, as I would experience much more intensely later for my children, is a unique, very strong, and moving experience. But since my interest was in the brain and in reconnecting with my early considerations about the mind and emotions, my clinical choice was definitely psychiatry. Yet, to use a sweeping formula, I thought that before becoming a psychiatrist, I should understand how the brain worked. Neuropharmacology, the kind of work I could do with Michel Schorderet, seemed like a good start.

Since his arrival in Geneva, Michel had moved from the rat superior cervical ganglion to the rabbit retina as a model for neurotransmission. Building upon the work of John Kebabian in Greengard’s lab, which revealed the existence of dopamine-stimulated cAMP formation in the caudate nucleus (Kebabian et al., 1972), and upon the discovery that dopamine was present in amacrine cells of the retina (for review, see Djamgoz and Wagner, 1992), Schorderet had just published an article showing dopamine-stimulated cAMP formation in the rabbit retina (Bucher and Schorderet, 1975). Greengard and his associates had just proposed that antipsychotics such as haloperidol were acting as antagonists at putative dopamine receptors coupled with the formation of cAMP in nervous tissue (Clement-Cormier et al., 1974). This connection with psychiatry immediately caught my attention. As I was digging into the literature on neurotransmission and signaling in the nervous system, I realized that novel neurochemical techniques were being developed to identify and characterize neurotransmitter receptors, using radiolabeled ligands. The name of one neuropharmacologist was standing out in the field, as far as I could judge: Solomon Snyder from Johns Hopkins. Using ligand-binding assays, his lab was publishing, almost weekly, the characterization and distribution of a given receptor (Enna et al., 1977), including the dopamine receptor (Burt et al., 1975). With Michel Schorderet, we decided that characterizing dopamine receptors (DR) in the retina would be a good project for me to start. These receptors had not been identified yet in the retina and the ligand-binding study also could contribute to the characterization of their pharmacological properties, as the evidence was emerging for the existence of two types of DR, DR1 and DR2, with the former thought to be positively coupled to cAMP formation (Garau et al., 1978).

After a few months, it became clear that rabbit retinas would not provide sufficient tissues to carry out the project. I was also struggling with highly nonspecific binding. Michel arranged a visit to the lab of a colleague who had set up the technique at Sandoz in Basel. The protocol that was used helped me clarify some of the methodological steps that could explain my lack of success, and the decision was made to use the much larger bovine retina. So, here I was, showing up early in the morning at the local slaughterhouse to collect eye bulbs of cows immediately after they had been put to death. The general ambiance was rather rough and exchanges were direct. One morning I arrived late: the first batch of animals had been slaughtered. One of the workers told me that I could grab some eye bulbs that had been thrown into a large bucket. I told him that I needed them when they were still warm and that I would wait for the next batch to be processed. As the first pair of eye bulbs was cut off from the head, I placed them into a Styrofoam box filled with ice. Several workers looked at me with surprise; one of them shouted “Hey young man, make up your mind: you just said that you wanted them warm, and the first thing you do, you put them on ice!” There was a big laugh. I felt quite embarrassed, made a big smile, and left without trying to explain my awkward behavior. Finally, after several months, experiments were starting to work. I could establish kinetic curves from the binding data and quantitatively determine the properties of the DRs using a variety of analytical tools, and I presented posters at a couple of local meetings.

On a personal level, I was going through a difficult time, a time of great doubts. First, my relationship with my wife Anna was falling apart. She was from a well-to-do family in Milano. We had met in Crans-Montana early during my studies at the medical school in Geneva, while she was finishing high school in Milano. We found the long-distance relationship unsatisfactory and decided that she would come to the Geneva to study sociology at the university. Given the social and cultural background in which we lived, it was unimaginable for two young people to live together without being married, which we did, obviously at a much too young age. After three years, we divorced in an amiable way. We had no children. Despite the nonconflictual nature of our separation, I was left with a feeling of failure. I also started to have doubts about my professional choice: what was I doing early in the morning in a slaughterhouse to collect bovine eye bulbs while my classmates were doing something useful like relieving the suffering of patients? I was also having doubts about the direction my research project was taking me: as much as I liked working with Michel, after a while, I was finding the receptor-binding experiments rather tedious and not intellectually challenging. Where was the biological question? Would this project help me understand how the brain worked? I felt so far from the exciting questions about the mind that had driven me where I was now.

Some difficult months during the spring of 1978 went by until I read an article published in Science two years earlier entitled “Endorphins: Profound behavioral effects in rats suggest new etiological factors in mental illness.” The first author was a scientist named Floyd E. Bloom from the Salk Institute in La Jolla, California (Bloom et al., 1976). I felt an incredible sense of relief and excitation at the same time. There, before my eyes, was the evidence that a chemical recently discovered in the brain could affect behavior and be related to a mental illness. There was an answer to my doubts; there was the lab that I wanted to be part of and the scientist with whom I wanted to work. The next day I wrote him a letter (no emails at the time) with my meager curriculum vitae that featured, in terms of publications, a couple of abstracts and an article in preparation. I received Floyd’s reply a couple of weeks later indicating that he would soon be in Milano for a conference and that we could meet there. I still am a very good sleeper, but the night before I met Floyd was sleepless. I was anxious and excited. We met in the cafeteria of the congress center: I was immediately struck by Floyd’s energy, quick mind, and charm. My English was average, yet sufficient to explain my previous work and my motivations. I could sense his impatience at my laborious discourse, but he listened very gently, smiling often. Floyd mentioned that he was aware of the work that Schorderet had done in Greengard’s lab, asked me if I was familiar with cAMP determinations, and did not seem particularly interested in receptor-binding experiments. He told me that we should reconnect a month later in Paris where he would be attending the International Union of Pharmacology meeting, and he would let me know at that time if he had positions available for the fall 1979. Our initial meeting in Milano lasted 15 minutes, but it felt much longer to me. In Paris, in a two-minute exchange, Floyd confirmed that I could join his lab. I hardly realized what he said and was left with the impression that the exchange might have been a fantasy. Shortly after I received a confirmation letter from Floyd, I applied for a fellowship from the Swiss National Science Foundation. Within a few months, I was awarded the fellowship. I had submitted the main findings on DRs in the retina (Magistretti and Schorderet, 1979) and presented my medical doctorate thesis to the University of Geneva Medical School. Such medical theses are in no way comparable to a doctoral thesis and, in fact, have been suppressed since. I wished I could have enrolled in a neuroscience graduate program, as I realized that the neuroscience education I had received during medical school was rather superficial. But there were no such programs in Switzerland. I mentioned this wish to Floyd, and he suggested that I explore possibilities at the University of California, San Diego (UCSD) campus once I was in San Diego.

On the personal level, things also looked on the bright side. In February 1979, I met a lovely girl, Christine, full of energy and with a great positive attitude toward life. She was finishing nursing school and was planning to continue her studies in the United States. Luckily, she eventually joined me in San Diego and enrolled in a bachelor program in psychology at Muir College at UCSD. In the meantime, I had been accepted in the biology graduate program in the same university. We both received some credits for our previous education in Switzerland and graduated with our respective degrees within three years.

The Salk Institute Years

I joined Floyd’s lab at the Salk in September 1979. The A.V. Davis Center for Behavioral Neurobiology, as the lab was named, was remarkable for the variety of experimental approaches that it comprised, electrophysiology, neuroanatomy, immunocytochemistry, electron microscopy, neurochemistry, and behavior, each component being overseen by a senior scientist. It was in fact a small neuroscience department. My direct supervisor was William (Bill) Shoemaker—a fine neurochemist trained at MIT in the lab of Richard Wurtman—who, like some of the other staff scientists, had followed Floyd to La Jolla from the Bloom lab in St. Elizabeth’s hospital at the National Institute of Mental Health. The lab atmosphere was very open, reflecting Floyd’s personality, with considerable exchanges and collaborations among its members. The role of noradrenaline (NA) as a neurotransmitter in the brain was still a strong research theme developed by several units of the lab, following up on the seminal observations made by Floyd and his associates at St. Elizabeth’s, George (Bob) Siggins and Barry Hoffer (Hoffer et al., 1971; Siggins et al., 1971). Despite the strong evidence of a neurotransmitter role for NA, based notably on iontophoresis studies showing that the application of NA affected the excitability of the Purkinje cells of the cerebellum (Siggins et al., 1971), it remained unclear which were the behavioral instances during which NA-containing locus coeruleus neurons would fire. Contrasting with the view from the Bloom lab that NA was a synaptically released neurotransmitter in its own right, Alain Beaudet and Laurent Descarries, two Canadian neuroscientists, suggested that NA was only marginally released at synapses but mostly from varicosities along noradrenergic axons, a modality of release that was questioning the nature of NA as a classical neurotransmitter. Their conclusions were based on the visualization by electron microscopy autoradiography of radioactively labeled NA in the cerebral cortex (Beaudet and Descarries, 1978). In Floyd’s lab, Steve Foote and Gary Aston-Jones were recording in vivo from the locus coeruleus of squirrel monkeys and rats. They showed that in awake behaviorally responsive animals, these neurons responded to non-noxious sensory stimuli from any modality, decreased their activity when animals were inattentive, and eventually became silent during rapid-eye movement sleep (Foote et al., 1980, 1983). These observations were taken as reinforcing the view that NA acted as a neurotransmitter in the brain.

The other main line of research in Floyd’s lab was the localization and function of newly discovered neuropeptides, such as somatostatin, opioid peptides, vasoactive intestinal peptide (VIP), neuropeptide Y, cholecystokinin, and corticotropin-releasing factor, as putative brain neurotransmitters. The lab next door was Roger Guillemin’s, who recently had shared the Nobel Prize with Andrew Schally for the discovery of hypothalamic-releasing factors. Guillemin’s lab, as well as that of Wylie Vale who had been Guillemin’s student before starting his own lab at the Salk, were providing peptides and their antibodies to Floyd and his associates to study their localization by immunocytochemistry and their actions on neuronal excitability. Although the immunocytochemical studies significantly contributed to mapping the field of several peptides’ cellular localization in extrahypothalamic areas of the brain (Chavkin et al., 1983; Morrison et al., 1983), the actions of the newly discovered peptides on neuronal excitability produced pleiotropic results, with few exceptions, such as for example for opioid peptides and somatostatin (Siggins et al., 1986; Pittman and Siggins, 1981). The scientific focus of Floyd’s lab being the role of NA and peptides, it is not surprising that the projects that I eventually developed in his lab would be concerned with the interactions between NA and a particular peptide, VIP.

Floyd’s lab had just been awarded a large grant to study the mode of action of lithium as a mood stabilizer in bipolar disorder, with a focus on noradrenergic transmission (Bloom, 2012). Floyd was looking for an assay to probe noradrenergic signaling after chronic lithium administration, that would be more sensitive than those available in the lab, which were responses to iontophoretically applied NA in hippocampal or cerebellar neurons, noradrenergic receptor sensitivity tested by ligand-binding assays, and the formation of the downstream second-messenger cAMP. None of these assays had provided any evidence for changes in noradrenergic signaling efficiency. Shortly after I joined the lab, Floyd visited the lab of Jean-Charles Schwartz in Paris where he became interested in an original assay for noradrenergic signaling in the central nervous system: NA-evoked glycogenolysis (Quach et al., 1978). What had caught Floyd’s attention was the sensitivity of the assay, which revealed an EC50 (the concentration of NA necessary to elicit 50% of the maximal effect) of NA that was 10 to 50 times lower than that observed for cAMP generation. This phenomenon had been described for the glycogenolytic effect of adrenaline acting at beta-adrenergic receptors in liver and muscle and was thought to result from the amplification of the signal at each step of the signaling cascade, from the receptor to cAMP formation, to phosphorylation of enzymes for glycogen metabolism, and eventually to glycogenolysis. Earl Sutherland had been awarded the 1971 Nobel Prize for the elucidation of this signaling cascade (Rall and Sutherland, 1958; Sutherland and Robinson, 1966).

The higher sensitivity of NA-evoked glycogenolysis suggested to Floyd that this assay could be useful to reveal a potential change in noradrenergic transmission in the brain of animals chronically treated with lithium. Upon his return, Floyd asked me to set up this assay, which looked relatively simple. It consisted of preparing, with a McIlwain tissue chopper, 350 um slices of the neocortex and incubating them in a standard Krebs-Ringer bicarbonate buffer in the presence of tritiated glucose. The energy crisis elicited by the decapitation-induced anoxia and the subsequent dissection of the neocortex, completely degrades endogenous glycogen stores. Consequently, incubation of the slices with tritiated glucose results in the resynthesis of tritiated glycogen with high specific activity. A steady state between synthesis and degradation usually is reached within 30 minutes at which point molecules can be applied to test their potential glycogenolytic effect. After inactivating the tissue by sonication followed by microcentrifugation, the supernatant is pipetted onto filters and tritiated glucose and glycogen are separated by ethanol precipitation, since glycogen precipitates on the filter while glucose is solubilized in ethanol. Filters containing the precipitated tritiated glycogen are then placed into vials and radioactivity determined by liquid scintillation (Quach et al., 1978). The assay turned out to be more difficult than it looked, possibly also because of my limited lab experience. Week after week I would do experiments with limited and inconsistent results. I became quite frustrated and felt awful because I knew I was disappointing Floyd who had so graciously accepted me in his lab.

My dismay became even greater one day, when Steve Foote, who was obviously strongly biased toward in vivo experiments, passed by while I was preparing slices and said with his baritone voice and sharp sense of humor: ”Pierre do you really think that you will understand how the brain works by chopping it up like you do?” I didn’t know what to say: maybe Steve was right; and while I admired Steve’s intellectual depth, I trusted Floyd’s acumen and intuition and kept working on the assay. Eventually, some encouraging results were coming, but not reproducible enough to apply them to test on a large-scale ex vivo experiment like the one Floyd had in mind. Floyd was being patient and empathic: as I told him that I was returning back to Switzerland for a short break in June, nine months after my arrival in San Diego, he suggested that I visit Jean-Charles Schwartz’s lab in Paris to perform the assay there. Tham Quack, the postdoctoral fellow who had set up the assay in Schwartz’s lab was very welcoming and helpful. Within a few days at the bench with him, I had identified the critical steps to improve the reproducibility and was able to implement it successfully in Floyd’s lab.

The role of the newly discovered peptides was increasingly becoming a central question in Floyd’s lab, and for that matter, for neuroscientists around the world who were interested in chemical neurotransmission. For example, Harvey Karten a specialist of the visual system, who was visiting the lab from SUNY had come to the Salk to study the localization of peptides in the retina, mostly the avian retina. His hypothesis was that specific subtypes of retinal cells would contain a specific peptide. This sort of code for neurotransmission was not confirmed, neither in the retina nor in other parts of the nervous system. What turned out to be the case, as shown by Tomas Hökfelt at the Karolinska Institute in Stockholm, was the co-localization within the same neuron of a peptide and a “classical” neurotransmitter, for example, NA and somatostatin (Hökfelt, 1977; Hökfelt, 1991). In terms of physiology, many open questions remained concerning the actions of neuropeptides in the brain. Within less than five years, the vocabulary of neurotransmission had expanded from a handful of molecules, such the amino acids gamma amino butyric acid, glycine, and glutamate (paradoxically questions about the actual role of the latter as a neurotransmitter remained until the early 1980s), acetylcholine, and the monoamines NA, serotonin, and dopamine, to a plethora of peptides, approaching two to three dozen (Bloom, 1977)! The notion of neuromodulators emerged, meaning that some of these peptides were somehow adjusting the actions of the classical neurotransmitters (Bloom, 1977; Siggins et al., 1982). This was an issue often debated during “Startrek,” the thought provoking weekly meetings of the lab. Francis Crick, who had recently joined the Salk Institute, was an active participant in these meetings, relentlessly chasing to the limit any hypothesis formulated about the role of neuropeptides. For all lab members, his was an intimidating yet stimulating presence.

Although I was quite satisfied that the glycogenolysis assay was working, the prospect of spending the next few months feeding lithium to dozens of rats to then probe their noradrenergic transmission seemed to me only moderately exciting compared with the challenge of revealing the role of neuropeptides in the brain. One day, as I was looking in the library for articles about neurotransmitter-evoked cAMP formation in neural tissues (no PubMed available at the time) I stepped on an article from Leslie Iversen’s lab, one of the towering figures in neuropharmacology at the time and a good friend of Floyd, showing that VIP induced cAMP formation in homogenates of the cerebral cortex (Quik et al., 1978). This observation sparked the following reasoning in my mind: NA stimulated both cAMP formation and glycogenolysis in the cerebral cortex. Why shouldn’t VIP do the same? This thought really excited me because, unlike cAMP formation, glycogenolysis served a physiological function, namely—by analogy with its role in liver and muscle—a mechanism to provide energy substrates. Possibly VIP would be glycogenolytic in the cortex. I decided to test this hypothesis with the assay that I had just implemented in the lab for NA. I admit that I was very optimistic: it seemed so logical. One day in November 1980, I came home and told Christine: “I just found out that VIP mobilizes energy stores in the brain. I think that this is a really important observation because it means that within the brain there are neurons that exert a metabolic function rather than directly modulate neuronal excitability.” Christine looked at me with her usual sweet and supporting smile and said, “Yes, I am sure that this is very important. Let’s celebrate.” We cooked “risotto alla Milanese” and opened a good bottle of red wine. I was euphoric.

I spent the next few days in the library to collect articles about glycogen metabolism in the brain. The literature search was scarce on this topic. I eventually found what is probably the first convincing demonstration of the presence of glycogen in the brain: a 1938 article in the Journal of Biological Chemistry by Kerr from the American University of Beirut (Kerr, 1938). More recent articles were from the lab of Oliver Lowry and Janet Passoneau from Washington University (Nelson et al., 1968) and some electron microscopy observations (Sotelo and Palay, 1968; Phelps, 1972). Two main features emerged from this search: (1) there is very little glycogen in the brain and (2) it is almost exclusively localized in a type of glial cell, the astrocyte, not in neurons! This came as a great surprise to me; I hardly knew what glial cells were, possibly a sort of inert connective tissue that kept neurons together. Had I known this information I probably would have never tested the glycogenolytic effect of VIP in the cortex. Why bother studying a molecule that was present in low amounts, ten to a hundred times less than in muscle or liver respectively, and in addition that was localized in a kind of inert cell type that likely was not active in information processing in the brain. Yet, as it turns out, my serendipitous encounter with glycogen and glial cells was going to determine the research field that I would develop over the next 40 years. Paradoxically, some degree of ignorance actually may be healthy. It prevents us from having preconceived notions and enables us to keep an open mind to explore uncharted paths.

Once I had a clearer view about glycogen in the brain, I presented the results to Floyd, stressing how a pharmacological assay developed to explore noradrenergic function led to an observation that could provide some insights for the study of cell-cell signaling in the brain. First, the glycogenolytic effect of VIP indicated that certain neurotransmitters could exert their effects on glial cells, which provided an opening to further studies of neuron-glia interactions. Second, this interaction implied the existence of a mechanism to couple neuronal activity to energy metabolism. Third, at least as far as VIP was concerned, there was now evidence for a physiological action of a newly discovered neuropeptide. The results and their discussion definitely caught Floyd’s attention: he was smiling and nodding his head as I was reciting these ideas. He said, “Fantastic,” and asked me if I needed more resources to move the project forward. Over the next few months, I worked relentlessly to complete the characterization of this metabolic effect of VIP and wrote up the results in an article published in October 1981 in the Proceedings of the National Academy of Sciences, entitled “Vasoactive intestinal polypeptide induced glycogenolysis in mouse cortical slices: a possible regulatory mechanism for the local control of energy metabolism.” I was particularly happy with the concluding sentence I had written:

A final observation can be made: VIP and norepinephrine display similar glycogenolytic actions in peripheral tissues. This action may indicate that certain substances with specific hormonal roles in several cell systems may exert similar homeostatic functions at the cellular level within the central nervous system, which are constrained by the spatiotemporal functional precision inherent to neural transmission. (Magistretti et al., 1981)

Indeed, the results suggested that certain neurotransmitters, such as VIP and NA, could exert hormone-like effects within the brain, acting in a nonsynaptic way (no synapses on astrocytes) on glial cells.

In the meantime, complementing these metabolic studies, I engaged with John Morrison on the immunohistochemical characterization of VIP-containing neurons in the cerebral cortex. John and I were sharing with four other post-docs a room on the top floor on the ocean side of the south wing of the Salk Institute. The view was simply magnificent: the canyon sloping down to the cliffs and then the Pacific Ocean. During the months of January and February, we would see pods of whales swimming south toward Baja California. Once they had reached the tip of Baja, they eventually would move north in the Sea of Cortex to give birth to their calves. The other post-docs did not use this room much, which was actually quite far from the lab, located in the basement on the east side. There was a feeling of quietness up there, which, along with the inspiring view, was conducive to the reflections that John and I liked (and still like 40 years on) to share about brain function. A long-lasting friendship started in that office. John, his wife Abbie, and his children Alex and Kelsey have become close friends with Christine, and our children. We still meet regularly and enjoy lively conversations sparked by great wines and food.

John (Figure 2) had joined Floyd’s lab in the summer of 1980 from the lab of Mark Molliver at Johns Hopkins. His doctoral thesis was about the immunohistochemical characterization of the noradrenergic innervation of the cortex (Morrison et al., 1978). Using an excellent antibody against dopamine beta-hydroxylase developed by Reinhardt Grzanna and Joe Coyle (Grzanna et al., 1978), John had revealed that intracortical noradrenergic fibers are organized tangentially, spanning from the rostral to the occipital poles with a trajectory parallel to the pial surface (Morrison et al., 1981). This particular organization suggested that noradrenergic fibers would exert their actions globally, throughout the cortex (Morrison et al., 1979). I remember John telling me that before immunohistochemistry, the cerebral cortex was taken as a negative control for the presence of NA, since the classical Falck-Hillarp histochemical technique could not reveal a signal for the presence of monoamine fibers (Falck et al., 1962). Because NA and VIP shared the same metabolic effect, we decided to characterize the morphology and distribution of VIP-containing neurons in the cerebral cortex. Using a selective antibody raised against porcine VIP, we showed that VIP neurons represent a homogeneous population of radially oriented intracortical bipolar cells spanning across the cortical thickness with a maximal dendritic span of 100 um (Morrison, et al., 1984; Magistretti and Morrison, 1985). This morphology indicated that VIP neurons were defining what one could consider cortical columns (Magistretti and Morrison, 1988). Following the advice of Floyd, we also performed a quantitative analysis of the density and distribution of these neurons. We used a rather rudimentary approach that involved identifying on transparent sheets the localization of the cell bodies of VIP neurons visible on horizontal sections and then piling up these sheets to perform a nearest-neighbor analysis (Morrison et al., 1984). This type of analysis, which took several weeks to accomplish at that time, can now be performed in minutes with similar results using quantitative neuromorphology software. Francis Crick became quite interested in this quantitative approach. John and I had the privilege of having several discussions with him, sometimes in the lab, looking at slides on a fluorescence microscope. We were of course thrilled by this unique opportunity and thanked him in the acknowledgment section of our article, which he had read and commented before submission (Morrison et al., 1984).

Fig. 2.   John Morrison (center), Gary Aston-Jones (left), and me. The Salk Institute, 1981. Photo credit: Jamie Simon

The combination of our neurochemical and morphological work was synthesized in a theoretical formulation whereby the VIP and NA neuronal systems in the neocortex were regulators of energy metabolism. VIP neurons within radially oriented cortical domains, or columns, translating incoming modality-specific inputs into a metabolic response, while the role of the NA system would be to prime metabolically a vast rostro-caudal expanse of neocortex across modality-specific regions (Figure 3) (Magistretti and Morrison, 1988). This proposal was consistent with work at the EM level by Alan Peters, which showed that VIP-containing neurons received direct thalamo-cortical inputs (Peters and Kimerer, 1981), and with the recently demonstrated role of the ceruleo-cortical system in non-noxious, attentional mechanisms described by Steve Foote and Gary Aston-Jones (Foote et al., 1983).

Fig. 3.   Graphic representation of the interaction between VIP neurons and NA fibers in the neocortex (Magistretti and Morrison, 1988). Vasoactive intestinal peptide neurons promote glycogenolysis in astrocytes. Given the bipolar nature of the VIP neurons, this effect is restricted to cortical columns. VIP neurons are activated by corticocortical and thalamocortical specific afferents (SA). The noradrenergic afferent (NA) fibers span horizontally across cortical domains and hence can metabolically prime a vast expanse of neocortex by promoting glycogenolysis in astrocytes. I–VI refer to cortical layers. W.M., white matter. Original drawing by Jamie Simon.

In the spring 1982, as I was getting ready to wrap up my work for the thesis, Silvio Varon who was my co-advisor as a UCSD faculty, came up with a proposal for some additional experiments. I valued very much Silvio’s insights: he had worked with Rita Levi-Montalcini at Washington University on pioneering studies of neurotrophic factors and recently had developed techniques for culturing neurons and astrocytes separately. He brought a complementary type of mentorship to that of Floyd. Still today, I realize how fortunate I have been to have had such remarkable advisors, yet with such different personalities. Silvio suggested that I study the glycogenolytic effect of VIP on the astrocyte cultures that had been recently established in his lab. Although this suggestion was logical and would complement my other studies, I was less than enthusiastic at this idea as I knew that it would postpone my thesis defense by several months. Nevertheless, I performed the experiments, which indeed demonstrated the glycogenolytic effect of VIP on astrocytes (Magistretti et al., 1983). I think that it was one of the very first demonstrations for the existence of neurotransmitter peptide receptors on glial cells. More important, it opened the way to further experiments I did throughout the next decades in my lab back in Switzerland.

In September 1982, I eventually defended my doctoral thesis at UCSD, entitled “Vasoactive Intestinal Polypeptide: A Regulator of Cellular Homeostasis in Cerebral Cortex” (Magistretti, 1982). On September 30, 1982, the day of my 30th birthday, I landed at Geneva airport, bringing back with me myriad memories that were going to shape my future. The years at Salk and UCSD determined my subsequent scientific journey. The Californian experience opened my mind to different lifestyles and values that would influence my personal life back in Switzerland.

In La Jolla, Christine and I lived in a one-bedroom flat close to the ocean on Windansea Beach. The years we spent in La Jolla are among the happiest ones in our life. We were experiencing a new cultural life, away from our social connections and family and the sometimes-overbearing environment in Switzerland, making new friends, and experiencing a great sense of novelty and freedom. We still jokingly ask to each other, “When are we going back to live in San Diego?”

Establishing a Lab in Geneva

I returned in the Department of Pharmacology of the Geneva Medical School, where I had studied and was first exposed to research. The department had moved, along with all preclinical departments, from the old medical school built at the end of the 19th century, into a brand new building close to the hospital. Despite the novelty, I felt a sense of déjà vu: I was sharing an office and a lab with Michel Schorderet, my medical thesis advisor. Granted, Michel was gracious and supporting, the space was modern and larger, and I had a position of maître-assistant (something between post-doc and assistant professor), but I was asking myself, “Am I really moving forward?” I saw myself stuck in a system that would at best allow me to slowly climb the academic ladder and become a professor, if I was fortunate, 20 years down the road. And how about the science: would I be able to develop original research projects that would bring me closer to my initial goal to understand the mind? Fortunately, the personal side was looking bright, and within a year, some exciting experimental results reassured me.

Christine and I settled in a nice apartment close to the lab and married in March 1983. The proceedings of the wedding ceremony brought us radically back to our own cultural environment, after the west-coast life that we had become so fond of. The ceremony was officiated by the senior Calvinist pastor in the Geneva Cathedral in the Old Town. After almost a millennium as a Catholic church, in 1535, the cathedral had become a protestant religious site, established by Jean Calvin. In 1506, Christine’s family, the Naville, had moved from the nearby Savoy Duchy to Geneva and her family was closely linked to the establishment of Calvinism in Geneva; hence, the certain formalism of our wedding ceremony. On July 20, 1984, our first child, Ambroise, was born. At the risk of appearing too sentimental, this day remains, along with those when our two other children, Bérénice and Henri were born, the nicest day of my life.

The first experiments I started in Geneva were to test whether an interaction existed between the VIP and NA neuronal systems in the cortex. Because NA was globally priming the cortex and the bipolar VIP neurons were activated by specific inputs, it was conceivable that they could interact within the cortical volumes where the two systems intersected. The readout for their potential interaction was cAMP formation. The results turned out to be positive, revealing a synergistic interaction between VIP and NA in forming cAMP; the pharmacological basis for this interaction was the potentiation by NA, acting at alpha1-adrenergic receptors, of the formation of cAMP induced by VIP (Magistretti and Schorderet, 1984, 1985). The signaling for this synergy was mediated by prostaglandins formed by activation by NA of alpha1-receptors (Schaad et al., 1987). These observations led me to propose that the two orthogonally oriented neuronal systems could generate cortical hot spots at their intersection when the ceruleo-cortical noradrenergic system and the radially oriented VIP neurons were simultaneously active, a behavioral modality achieved during an attention-associated specific sensory input (Magistretti, 1990). This project, which resulted in two Nature articles (Magistretti and Schorderet, 1984; Schaad et al., 1987), gave me a great boost for establishing my group and obtaining my first grant from the Swiss National Science Foundation, which I then received without interruption for the next 33 years.

From 1983 to 1988, I continued to further characterize the signaling mechanisms of VIP and the coupling between neuronal activity and energy metabolism in various central nervous system regions. With my first graduate student, Jean-Luc Martin, we decided to study the molecular mechanisms for VIP release from the cortical bipolar neurons that contain it. Indeed, a striking feature of these neurons is their strong staining by immunohistochemistry that reveals a Golgi-like appearance and indicates the presence of VIP in dendrites (Morrison et al., 1984). We identified a particular voltage-sensitive calcium channel that was necessary to trigger release, as well as a key role of arachidonic acid metabolites in this process (Martin and Magistretti, 1989a, 1989b). With my other student, Patrick Hof, who had just completed his medical studies at the University of Geneva, we found that potassium, at concentrations that are reached in the extracellular space during physiological neuronal activation, promoted glycogenolysis, adding a new player to the activity-dependent neuron-glia metabolic coupling (Hof et al., 1988). Interestingly, two decades later the labs of Brian McVicar and Felipe Barros independently described the involvement in this process of a potassium-dependent sodium–bicarbonate exchanger activating adenylate cyclase (Ruminot et al., 2011; Choi et al., 2012). We eventually also showed that adenosine, which is similarly released by active neurons, is a glycogenolytic agent (Magistretti et al., 1986).

Thirty-five years on, I have continued to collaborate with Jean-Luc Martin. We currently are collaborating on the role of lactate, the metabolite formed by glycogenolysis in astrocytes, as an antidepressant agent, a recent result that I will discuss later (Carrard et al., 2016). As to Patrick Hof, after a couple of years in my lab, he joined John Morrison’s group at Scripps Research Institute, where Floyd’s lab had moved from Salk in 1985. Patrick has gone on to a brilliant career as a distinguished comparative neuroanatomist and is now vice chair of the Department of Neuroscience at Mount Sinai School of Medicine. He is also the editor-in chief of the respected Journal of Comparative Neurology. With Jean-Luc and Patrick, we also collaborated during those years with José Maria Palacios, Chema as he was dubbed, who had set up a kind of “factory” at Sandoz in Basel, to characterize by autoradiography the localization of a variety of neurotransmitter receptors. In his freezers, you could select sections of your preferred species and brain region. This collaboration led to several publications on the distribution of VIP receptors (Martin et al., 1987; Hof et al., 1991).

In 1986, Professor Ralph Straub, the chair of the Department of Pharmacology at Geneva Medical School, suggested that I apply for a new funding scheme of the Swiss National Science Foundation called START, an acronym for Swiss Talents for Academic Research and Teaching. It was essentially a career development award aimed at supporting young promising academics who potentially could apply for professorial positions in the years to come in any academic discipline. Ralph Straub was a short, discreet, and shy man who frequently brought to his office a big Dane, named Dasso. As you entered Straub’s office, Dasso would move toward you with his big mouth open: needless to say, you would not do or request anything that could upset him or his owner. Straub was a fine neurophysiologist trained in the British school of physiology of axonal conduction. He had worked with Richard Keynes and Murdoch Ritchie and had published a few articles in late 1950s and early 1960s with Paul Greengard on conduction and metabolism in the rabbit vagus nerve, a preparation that Straub continued to study until his death in 1988 (Greengard and Straub, 1959, 1962). Interestingly, these studies by Greengard and Straub were already focused on the metabolic cost of neuronal (axonal) activity. In January 1987, I was one of the first four awardees of the new START program and decided to take a sabbatical and return to Floyd’s lab, now at the Scripps Research Institute, to learn some molecular biology, an approach that Floyd had just introduced in his lab.

As we landed in San Diego in October 1987, Christine and I felt like we were returning home, now with our small family including Ambroise and Bérénice, who was born a few months earlier. We rented a house in Del Mar Heights located in Lozana Road, a name that was prophetic of events to come shortly. All the dear friends that we had left a few years earlier were still there and incredibly welcoming: of course Floyd and his charming wife Jody, John and Abbie, Bob Siggins, and Tibor Safar. Tibor deserves a special mention. One could define him as a hippie 20 years after it was in fashion, but doing so would not do justice to the wonderful person that he is: a true hedonist living without compromises for quality, in particular, as far as food and wine are concerned, and friendship. He had received a doctorate in psychology from UCSD, but he worked in a specialty shop in Sorrento Valley that produced Plexiglas lab equipment. As of today nobody really knows where his house is and even if he has one. To my great delight, I joined again the reunions of what its members like to consider the most exclusive wine tasting club in the world: the LJB&T, the La Jolla Bragging and Tasting Club. It was founded in 1981 while we all were at Salk, by Floyd, John, Bob, Tibor, Cary Lay (who eventually became professor at University of Indiana), and Joe Rogers (who left in 1982, for a position at Boston University). We did blind tastings, each one of us bringing one or more bottles: most of the time we made fools of ourselves in trying to identify the wines. Since 1984, when the Society for Neuroscience meeting was held in New Orleans, we have held a reunion of the LJB&T in a good restaurant on the first evening of the meeting, and we taste many great bottles of wine. All of us are quite fond of this reunion.

In April 1988, while I was enjoying my found-again life in San Diego, Professor Straub called and said that I should apply for a full professorship at the Medical School in Lausanne. His argument was that, while the START program could support the awardees for up to nine years, they were requested to apply for any professorial position that opened up in a Swiss university in her or his field. Professor Michel Dolivo, a neurophysiologist and chair of the Institute of Physiology at the Medical School of Lausanne, was retiring in the fall of 1988 and the search for his replacement was on. Straub mentioned that my chances to be appointed to this position were close to nil, given my far too young age, but he thought that it would be a good move to get my file known by some prominent Swiss academics who were part of the search committee. I flew back to Geneva for a week, and without much enthusiasm, I prepared the application. During the month of May, events accelerated. First, I received a phone call from Jean-Luc Martin telling me that Professor Straub had suddenly died of a heart attack and that I was expected to return to Geneva as soon as possible. Second, a few days later I received a notice from the search committee that I was shortlisted for the position at the University of Lausanne, which provided yet another reason to cut short my stay in San Diego.

For the position in Lausanne, I gave two lectures, one aimed at students and one presenting my research and future plans, and I was interviewed by the search committee. Within a couple of weeks, I was informed that I was the first choice of the search committee, and in August, one month before my 36th birthday, I received the official appointment to the position of full professor (professeur ordinaire) at the Institute of Physiology of the University of Lausanne. Things had definitely accelerated, taking a completely unexpected turn. In the meantime, since the position of Professor Straub had become vacant, the University of Geneva Medical School had offered me an associate professor position, considering that I was too young for a full professorship. I faced a dilemma: I had just bought an apartment in Geneva, near the Medical School and my lab was running well. I would have to commute every day to Lausanne (an almost three-hour commute overall each day) if I accepted the position there. I sought advice from several people I trusted. I recall in particular a discussion with the chair of medicine in Geneva, Professor Alex Muller, who had a special aura in the Medical school and whose lectures in internal medicine had struck me for their clarity. He had no hesitation: the move to a new environment such as Lausanne, a very good university providing appreciable support, was much better than staying in a place where I had been since I was a medical student, in addition to the significant difference in professorial positions that I was being offered. In Muller’s thinking, this was an opportunity not to be missed. He very graciously said that it would be Geneva’s loss. I am still today very grateful to the University of Lausanne who entrusted me and provided a unique opportunity for a professional experience that, at least in Switzerland, occurs usually a decade later in one’s scientific career.

The Astrocyte Neuron Lactate Shuttle

The Institute of Physiology in Lausanne was located in a 19th-century building, close to the hospital. Until the 1950s, the chairs of the Institute lived with their families on the top floor. The building underwent several renovations over the years. My new lab was located in an annex built in the 1970s. I had to start everything from scratch: equip my lab, hire personnel, prepare my lectures and develop practical demonstrations for students, and participate in administrative tasks. The other three, more senior, full professors were very helpful. In particular Eric Jéquier, an internationally recognized expert in human energy metabolism and nutrition, who had been appointed chair, was very supportive: he made sure that I had enough time to develop my research and that I would not be “burned” by the task of combining it with heavy teaching and administrative loads. I am grateful to him for his benevolent support, which lasted until I took over the chairmanship when he retired 10 years later.

I decided to focus on what I considered my core biological question: what are the mechanisms that couple neuronal activity to local energy delivery? I had identified four neuronal signals that could mobilize energy from astrocytes by promoting glycogenolysis: VIP, NA, adenosine, and potassium (Magistretti et al., 1981; Magistretti et al., 1986; Magistretti and Morrison, 1988; Hof et al., 1987). I had a burning question that I wanted to tackle: how does glucose enter the brain parenchyma in register with neuronal activity, possibly to replenish the glycogen stores mobilized by activity (Swanson et al., 1992)? Lou Sokoloff had developed the elegant 2-deoxyglucose autoradiographic technique, which allowed for the determination of basal and activity-dependent glucose utilization in a variety of laboratory animals (Sokoloff et al., 1977). The technique recently had been extended to functional brain imaging in humans using ¹⁸F-2DG positron emission tomography (PET) (Sokoloff, 1981). The technique was powerful and its application to human functional brain imaging represented a major breakthrough, yet it was not affording a cellular resolution. The dogma was that glucose would enter directly neurons from the circulation. Because of my interest in astrocytes and the fact that intraparenchymal brain capillaries are literally covered by particular astrocytic processes called end-feet, I wondered whether glucose would not transit through astrocytes before reaching neurons. An elegant experiment by Lou Sokoloff on the autoradiographic localization of 2DG following somatosensory stimulation had caught my attention: the label was localized in the synapse-rich dorsal horn rather than in the dorsal root ganglia, where the cell bodies of the sensory neurons are located (Kadekaro et al., 1985). This observation along with the fact that many synapses are surrounded, at least partially, by astrocytic lamellar processes, where receptors for neurotransmitters had been recently identified, suggested to me that astrocytes definitely could sense synaptic activity and couple it to the uptake of glucose entry into the brain parenchyma (for review, see Magistretti and Allaman, 2015). We therefore set up the 2DG technique in the lab to monitor potential neurotransmitter-evoked glucose uptake in cultured astrocytes. In particular, because VIP and NA promoted glycogenolysis, I wondered whether they also could promote glucose uptake as a mechanism to replenish glycogen stores in astrocytes.

This study was implemented by a graduate student, Naichen Yu, whom I had met in China during a course sponsored by the World Health Organization, along with Nephi Stella, another student who had joined my lab as part of a co-tutelle thesis with Jacques Glowinski at the Collège de France in Paris. Naichen and Nephi showed that, indeed, NA-stimulated glucose uptake in astrocytes. The signaling mechanism did not involve cAMP, but rather activation of cyclo-oxygenase and arachidonic acid formation (Yu et al., 1993). Not surprisingly, VIP was without effect, as the observed effect was not cAMP dependent. Both Naichen and Nephi, completed their theses and went on as post-docs in San Diego: Naichen worked in Floyd’s lab first and then as a staff scientist at Merck; Nephi started working on endocannabinoids in Daniele Piomelli’s lab at the Neurosciences Institute in La Jolla, a research program that he has since developed successfully at the University of Washington in Seattle, where he has been for several years now as full professor in the Department of Pharmacology.

In 1991, a Canadian post-doc, Luc Pellerin, joined my lab after completing his doctoral thesis with Leon Wolfe at the Montreal Neurological Institute. With him, I extended the study of glucose uptake by astrocytes to other neurotransmitters and found some interesting results with glutamate. Indeed, glutamate not only stimulated glucose uptake but also promoted lactate production by astrocytes (Pellerin and Magistretti, 1994), a biochemical pathway known as aerobic glycolysis or the Warburg effect (Warburg, 1956). Furthermore, this effect of glutamate was mediated by its uptake through sodium-coupled transporters and not by receptors. This observation identified a second mechanism by which neuronal activity—in this case mediated by glutamate, which is released at 80% of the synapses in the cerebral cortex (Braitenberg and Schuz, 1998)— is coupled to energy delivery (Figure 4). Over the next few years, through the work of several students and post-docs, we described the key molecular steps that mediate this process for neuron-glia metabolic coupling. In brief, glutamate uptake by astrocyte-specific transporters, which is driven by the electrochemical gradient of sodium with a stoichiometry of one glutamate for three sodium ions, results in activation of the alpha2 subunit of Na/ATP-ase. Through this process, one ATP molecule is consumed to extrude three sodium ions (Pellerin and Magistretti, 1997). Glutamate taken up is converted partially to glutamine by glutamine synthase, also at the expense of one ATP molecule, and is transferred back to neurons to replenish the neurotransmitter pool of glutamate, through a mechanism known as the glutamate-glutamine cycle (Berl et al., 1968).

Fig. 4.   My lab at the Institute of Physiology of the University of Lausanne Medical School. Pictured left to right are as follows: (Front row) Jean-Marie Petit, Béatrice Roth, Selma Abdelmoumene, Sabrina Zerarka, myself, Jean-Luc Martin, Isabelle Jammes, Igor Allaman. (Back row) Maria Kiraly, Jean-Marie Brunet, Mauricette Maillard (partly hidden), Hubert Fiumelli, Hugues Cadas, Pierre Marquet, Karine Pierre, Stavros Therianos, Jean-Yves Chatton, Ruth De Bernardi.

We then characterized the cell-specific distribution of key molecular operators of glutamate-stimulated aerobic glycolysis, including in the human brain. By this means, we demonstrated that lactate dehydrogenase 5, the isoform of the enzyme that favors the conversion of pyruvate to lactate, is only present in astrocytes, whereas neurons express exclusively lactate dehydrogenase 1, which is also present in tissues like the heart that can use lactate as a substrate (Bittar et al., 1996; Laughton et al., 2000). We also showed a cell-specific distribution of monocarboxylate transporters (MCT), with MCT1 and MCT4 present in astrocytes and MCT2 present only in neurons (Bröer et al., 1997; Pellerin et al., 1998; Pierre et al., 2000). This set of observations led to the formulation of the Astrocyte Neuron Lactate Shuttle (ANLS) model (for review, see Pellerin and Magistretti, 2012; Magistretti and Allaman, 2015, 2018). As I coined these terms, I was reassured by the fact that lactate shuttles also had been recently described in muscle (Brooks, 1986, 2018).

As I presented the ANLS model at conferences (Figure 5), I experienced a strong resistance from classical neurochemists, sometimes in vehement terms. I still remember that one of the first times I did so, a senior neurochemist took the floor and said, “Pierre, what you just presented is a major conceptual step backwards.” Two points in the ANLS model were difficult to swallow for experts who had studied brain energy metabolism for decades: first, the main site for glucose uptake was in astrocytes, and second, the energy substrate that was delivered to neurons was lactate, which generally was considered a metabolic waste product produced by ischemia and anoxia, despite the fact that Henry McIlwain had shown in the 1950s that lactate in the presence of oxygen is a perfectly adequate energy substrate to sustain neuronal activity (McIlwain, 1953). Fortunately, I also found early support for the ANLS model, particularly so in functional brain imaging circles, which were certainly more open to novelty. This support included Lou Sokoloff, who replicated our original findings (Takahashi et al., 1995; Itoh et al., 2003). I had, and still have, very stimulating exchanges with Marc Raichle, one of the pioneers of in vivo brain metabolism studies. Marc published an observation that also generated some resistance: in PET studies, he described the occurrence of an uncoupling between glucose utilization and oxygen consumption during neuronal activation (Fox and Raichle, 1986; Fox et al., 1988). Biochemically, that meant that glucose taken up during neuronal activation was not fully oxidized, a conclusion consistent with the glutamate-evoked aerobic glycolysis and lactate production that we had described (Pellerin and Magistretti, 1994). The controversy about the ANLS model went on for several years, particularly in neurochemistry meetings and journals, mostly on theoretical grounds (Bak and Walls, 2018). Despite this resistance we, and others, were publishing experimental results in support of the model (e.g., see Cholet et al., 2001; Voutsinos-Porche et al., 2003; Bernardinelli et al., 2004; Magistretti and Chatton, 2005) (for review, see Magistretti and Allaman, 2018; Weber and Barros, 2015; Barros and Weber, 2018).

A major confirmation of the ANLS model came through a fruitful collaboration with Cristina Alberini, at Mount Sinai School of Medicine and now at NYU. We had gathered, through work in the lab in Lausanne, evidence that the expression of certain genes involved in the ANLS—in particular, in glycogen metabolism—were upregulated in the hippocampus following spatial learning and fear conditioning (Cardinaux and Magistretti, 1996; Allaman et al., 2000; Tadi et al., 2015). This observation pointed at glycogen and lactate, the main metabolite formed by astrocytes. With Cristina and her colleagues, we showed that pharmacological blockade of glycogenolysis in the hippocampus prevented long-term potentiation and memory consolidation in a manner that was rescued by intrahippocampal lactate delivery (Suzuki et al., 2011). This result, along with several others, led us to conclude that the transfer of lactate from astrocytes to neurons is necessary for memory consolidation (Suzuki et al., 2011; Gao et al., 2016). These findings, which were published in Cell, were quite antidogmatic as they showed that a molecule considered to be a metabolic end-product and a cell type considered to be some sort of “brain glue” were necessary for memory. Recently we extended these data through an electron microscopy study in a novel object recognition paradigm and found that learning increases the number and size of both dendritic spines and astrocytic glycogen granules in the hippocampus (Vezzoli et al., 2019). Blocking glycogenolysis during training inhibits the increase in the number of dendritic spines in a manner that is reversed by lactate (Vezzoli et al., 2019).

Work on the ANLS represented the main scientific focus of my lab at the Institute of Physiology at Lausanne Medical School until 2004 (Figure 5). That year, I was offered the directorship of the Douglas Research Institute in the Department of Psychiatry at McGill; the appointment came with the support of a senior Canada research chair. After 15 years in the Institute of Physiology and still in my early 50s, I felt ready for a new challenge. When I announced that I was going to leave Lausanne, the academic authorities moved fast. Within one week, I was appointed director of the Center for Psychiatric Neuroscience in the Department of Psychiatry, for which I had been a strong proponent within the Medical School. It was also agreed that I would have a joint appointment in the newly created Brain Mind Institute (BMI) at Ecole Polytechnique Fédérale de Lausanne (EPFL). My intention to move to Montreal was genuine, and Christine and I were very much looking forward to this cultural change. Ambroise had left Lausanne to study biochemistry at University College in London. Bérénice had been accepted to study economics at McGill, and Henri, our third child born in 1990, had been accepted in a very good high school in Montreal. McGill had been forthcoming in ensuring that Christine would be able to continue the type of work that she was doing through the foundation that she had just started, developing programs to fight poverty and support the reproductive health of women in the slums of Mumbai. We had found a house in Montreal and arranged for the move. The offer from Lausanne caught me by surprise. It touched on two points that I was particularly sensitive to: being part of the launch of two new institutes. One of these centered on biological research in psychiatry, a topic that had been my main motivation to engage in neuroscience. The other was destined to become one of the premier institutes of neuroscience in Europe, given the ambition and resources that it had been allocated. It would be an understatement to say that the choice was difficult. Eventually, I decided to accept the offer by Lausanne. The appointment at the BMI at EPFL was rapidly implemented. In fact, shortly after joining the BMI, Patrick Aebischer, the president of EPFL and a neurobiologist himself, asked me to take over the directorship of the BMI from Henry Markram to allow Henry to focus on his pet Blue Brain Project, which was a truly original and pioneering modeling effort in neuroscience, jointly developed between IBM and EPFL. Eventually the Blue Brain Project morphed into the Human Brain Project, one of the flagship projects of the European Community. Within a few months, without having planned it, I found myself working in two new neuroscience institutes.

Fig. 5.   Astrocyte-Neuron metabolic coupling. First graphic representation of the Astrocyte Neuron Lactate Shuttle (Pellerin and Magistretti, 1994).

In the course of the experiments we did with Cristina Alberini, we reported that, unlike lactate, glucose could not efficiently replace the blockade of glycogenolysis to rescue memory consolidation (Suzuki et al., 2011). This observation led us to think that energy deficit was not the cause of amnesia. After a long search, through work led by Igor Allaman, one of the pillars of my lab over the past 20 years, we found that lactate, and not glucose or pyruvate, induces the expression of genes involved in neuronal plasticity through the potentiation of N-methyl-d-aspartic acid (NMDA) receptor signaling (Yang et al., 2014). These observations indicated that lactate is not only an energy substrate but also a signaling molecule. A recent review expands on the notion that lactate in the brain should no longer be considered a metabolic waste product but is actually a signaling molecule (Magistretti and Allaman, 2018). Current experiments in the lab are actively exploring the molecular mechanisms of this action of lactate on NMDA receptors. Changes in the redox state of neurons evoked by lactate seem to play a critical role.

In fact, having identified the role of lactate produced by astrocytes has opened a Pandora’s box. Thus, we and others have shown that lactate is involved in other behavioral paradigms related to neuronal plasticity, such as addiction (Boury-Jamot et al., 2015) and the sleep-wake cycle (Petit et al., 2013; Petit and Magistretti, 2015). Lactate exerts neuroprotective effects (Berthet et al., 2009; Allaman et al., 2010; Morrison et al., 2012; Berthet et al., 2012; Bouzat et al., 2014; Carteron et al., 2018) via mechanisms that have been at least partially identified (Bliss et al., 2004; Bélanger et al., 2011a, 2011b; Jourdain et al., 2016, 2018; Margineanu et al., 2018; Tauffenberger et al., 2019) With my long-time collaborator Jean-Luc Martin, we recently have shown antidepressant effects of lactate in three animal models of depression (Carrard et al., 2016). Somehow I have the impression that we are witnessing a rehabilitation of lactate in the brain (Magistretti and Allaman, 2018) in a manner analogous to what occurred for glutamate in the late 1970s. Indeed, when I entered neuroscience, there were doubts as to whether glutamate, a metabolic intermediate of energy metabolism, actually could act as a signaling molecule in the nervous system. Today, nobody would question that glutamate is the main neurotransmitter in the brain, released at the majority of synapses (Braitenberg and Shuz, 1998). The story for lactate may well unfold in a similar way, in this case pointing at a role for lactate as a glia-derived signaling molecule.

Service Engagement and Outreach

As mentioned earlier, during the 1990s, I was able to focus almost exclusively on my research, thanks to the ideal conditions that I was offered at the University of Lausanne and to the shield from excessive teaching and administration that the chair of physiology, Eric Jéquier, generously provided to me. By the end of the decade, however, I had become increasingly involved in a variety of engagements at the medical school and in learned societies. I guess that this is inevitable as a career matures; the process was certainly enhanced by my reluctance to say “no” when approached about committing some time to the community. Among the positions that I accepted, I recall very fondly my presidency (2002 to 2004) of the Federation of European Neuroscience Societies (FENS). FENS was born from the ashes of ENA, the European Neuroscience Association, which by the end of the 1990s had lost, for a variety of reasons, its ability to represent the burgeoning neuroscience community that was developing in Europe. A group of presidents of national neuroscience societies (I represented Switzerland as the first president of the newly established Swiss neuroscience society) met in 1997 and drafted the vision for a new umbrella society for European neuroscience. The winning concept was the establishment of a biennial forum, which over the years has become a vibrant and scientifically outstanding international neuroscience gathering. My presidency was responsible for the fourth forum, which took place in Lisbon. The chances of success of this fourth forum were uncertain, because of the still-fragile nature of FENS, which was in its infancy, and because of the limited membership of the local neuroscience society. The Iberian solidarity worked very well, however, as flocks of Spanish neuroscientists were in attendance along with an excellent participation from across Europe, particularly from young neuroscientists, a feature that continues to characterize the FENS forums.

In the spring of 2008, Torsten Wiesel and Carlos Belmonte contacted me to ask if I was interested in the position of secretary general of the International Brain Research Organization (IBRO). I didn’t know much about this organization, except that like ENA at the end of the 1990s, it had become dormant, but it recently had been reenergized by Torsten and Carlos. Carlos explained to me how the contribution of IBRO to international neuroscience was vital, through the promotion of education, training, and research not only in economically well-developed parts of the world, but also, and more important, in less favored countries. I vividly remember when I received the call: I was in the small apartment where I was living with Christine in the Marais neighborhood of Paris, preparing my lectures for the Collège de France, where I had been appointed to the 2007–2008 international chair. The Collège provides a very special academic environment: it was founded by King François I in 1530 and its professors mainly teach to a public audience the original research that they are conducting. The intellectual heroes of my adolescent years, Roland Barthes, Claude Lévi-Strauss, and Michel Foucault occupied permanent chairs. I felt privileged to have been selected for one of the annual chairs. When I received the call from Carlos, my mind was somehow floating in the ethereal atmosphere of the Collège and I had a hard time fully appreciating what kind of time commitment accepting the position of IBRO Secretary General would entail. Of course, I could not refuse a proposal coming from two neuroscientists I greatly admired. Later, I actually became president of IBRO (2014–2019). It has been an enriching experience during which I have seen how an organization like IBRO can literally change the life of so many young neuroscientists worldwide, by providing them with opportunities for education that in many cases lead to amazing professional success. This came as a lesson and incentive to relentlessly mobilize all efforts to nurture talent worldwide.

Over the past 20 years, I also have been committed to neuroscience outreach. I think that as scientists, it is our duty to reach out to the public and explain the nature of our research. In these efforts I have been associated with the Dana Alliance for Brain Initiatives, in particular its European Dana Alliance for the Brain (EDAB). The Dana Alliance was founded by David Mahoney, a visionary businessman who captured the need for neuroscience outreach. The Dana Alliance has established the now extremely popular yearly “Brain Awareness Week” occurring worldwide every second week of March.

Recent Years

As I was approaching my 60th birthday I began to seriously worry about what would happen when I would reach 65, the mandatory age for retirement in Switzerland. I was certainly not ready to bring my research projects to a halt. I started looking in obvious places, such as the United States or Singapore. An unexpected opportunity entered in my reflections: Stefan Catsicas, a former vice-president of EPFL, and a dear friend from the time of Floyd’s lab at Scripps and later in Lausanne, had been appointed provost at a brand new university in Saudi Arabia: King Abdullah University of Science and Technology (KAUST). He proposed that I helped him as dean, to establish a division of biology and environmental sciences there. I visited the campus in the winter of 2011 and was stunned by the place, like everyone who visits KAUST for the first time. This coed and graduate-only university was established in 2009 on the shores of the Red Sea; it has considerable resources, the main one being the quality of the faculty that it has recruited. In the spirit of its founder, the late King Abdullah, KAUST was to reproduce the House of Wisdom in Baghdad at the turn of the first millennium, where the best scholars, independent of nationality and religion, would gather to advance knowledge. Though very new, KAUST has achieved considerable progress, ranking as the number one university in the world over the past four years in terms of citations per faculty.

Thanks to KAUST, I have been able to continue developing research projects there, in fact even expanding them in collaboration with EPFL. This new work is in areas that I was initially not considering, such as for example modeling and digital reconstruction of neuron-glia interactions, as KAUST provides an amazingly strong environment in computational sciences (Cali et al., 2016, 2019; Coggan et al., 2018, 2019). Corrado Cali and Hubert Fiumelli have been instrumental in setting up the lab at KAUST. Corrado recently was appointed assistant professor at the University of Torino in Italy. Hubert had been a graduate student in my lab in the 1990s. He spent six years with Mu-ming Poo at Berkeley, before returning to Lausanne to work with Jean-Luc Martin at the Center for Psychiatric Neuroscience (CNP). With some hesitation, Hubert took on the challenge to set up a lab with me at KAUST, but he is now enjoying life on the shores of the Red Sea. I continue research projects in Lausanne with Jean-Luc Martin at the CNP, of which I was the founding director from 2004 to 2012.

Establishing the CNP had been the inspiration for an initiative that I began in 2010. The Swiss National Science Foundation launches, usually every three to four years, very competitive calls for applications for National Centers for Competence in Research (NCCRs). The main goal of the NCCRs is the promotion of scientific excellence in areas of major strategic importance for the future of Swiss research, economy, and society. In 2010, we were awarded the NCCR SYNAPSY, one of the eight NCCRs awarded out of 60 applications, with the goal to establish a strong collaboration between basic neuroscientists and psychiatrists through well-integrated research projects based on clinical cohorts. The NCCR SYNAPSY aimed also to introduce a neuroscience culture in the Department of Psychiatry with the target of training promising young clinicians and promoting the emergence of a new generation of psychiatrists strongly grounded in neuroscience. The NCCR SYNAPSY has been renewed for a total of three four-year phases. When I stepped down as director in 2016, the directorship was assumed by Alexandre Dayer, a talented psychiatrist and neuroscientist who embodies the spirit of the NCCR. It is rewarding to see that, now 10 years on, more than 10 early members of the NCCR SYNAPSY have been appointed to professorial positions in the Departments of Psychiatry of the Universities of Geneva and Lausanne. A NCCR SYNAPSY member, Pierre Marquet, has been awarded a senior Canada research chair in the Department of Psychiatry at Laval University in Quebec. All of these individuals developed a dual career as clinician scientists who were practicing psychiatry.

Pierre Marquet, a remarkable scholar and physician, had joined my lab just before my move to EPFL, as part of the MD-PhD program. He previously had graduated in physics from EPFL and had enrolled in medical studies in Lausanne, eventually completing a full training in clinical psychiatry. Leveraging his strong physics background, particularly in optics, we applied digital holographic microsocopy—an advanced imaging technology that Pierre had developed with his master advisor at EPFL, Christian Depeursinge—to biological questions. This interferometric technique allows the visualization of ionic fluxes and cellular dynamics noninvasively and without any dye (Jourdain et al., 2011; Marquet et al., 2013). This experience showed me the incredible gains that can be achieved by establishing a biology lab in a technology school such as EPFL.

Coda

I am fascinated by what I would call, for lack of better words, the tricks that life plays on you. In my teens, I was interested in understanding the mind and concluded that I should study the brain. As I finished medical school, psychiatry was my clinical interest, but I postponed it to try first to understand how the brain worked and engaged in graduate studies in neuroscience. Thirty or so years later, here I was, after a winding journey through brain metabolism, astrocytes and a variety of signaling molecules and energy substrates, a professor of psychiatry, steering together with competent colleagues a major research effort involving large cohorts of psychiatric patients and even exploring experimentally mechanisms of depression.

I feel as if there were a force, like a magnetic field for paramagnetic molecules, which orients your life, unbeknownst to you, toward a certain goal. Some call it God, others a metaphysical force, others randomness in a complex self-organizing system. The psychoanalytical theory has suggested the terms of drive and libido. Unfortunately, these terms have had, from the beginning of Freud’s writings, a strong association with sexuality, but they in fact encompass all aspects of life. Over the years, I have given considerable thought to the psychoanalytical theory. In fact, I underwent a personal psychoanalytic experience and eventually wrote two books and several articles with a colleague psychiatrist and psychoanalyst François Ansermet (he was not my analyst) (Ansermet and Magistretti, 2004, 2010; Tran The et al., 2018; Arminjon et al., 2010). François is the former chair of the Department of Psychiatry at the University of Geneva: he is the most open-minded psychoanalyst I know, a scholar, a great clinician, and above all a wonderful person. Expanding on my personal considerations about the psychoanalytical theory is beyond the scope of this essay; these were developed in the two books with Ansermet. However, I think that it is worth mentioning here the notion of unconscious drive, which is linked to what Freud defined as the pleasure principle. This unconscious drive can account for the sort of force that brings you to situations that come as a surprise. This notion is not far from the theory of decision-making elaborated by Antonio Damasio in his writings, notably “Descartes’ error” (Damasio, 1994; Arminjon et al., 2011). Of interest is also the fact that John Maynard Keynes referred to the role of what he called “animal spirits,” in decision-making processes in economics and finance (Keynes, 1936).

This past decade has been intense, with all the engagements that I have followed up to now, coexisting: research projects in Lausanne and KAUST; service and administration with IBRO and KAUST; translational activities with the NCCR; and a recent initiative, the creation of GliaPharm, a spin-off from my lab at EPFL co-founded with Sylvain Lengacher, a collaborator of mine since the mid1990s, Charles Finsterwald, who was trained by my first graduate student Jean-Luc Martin, and my son Ambroise. Not surprisingly, I can’t help thinking that GliaPharm is somehow a reflection of my scientific and personal life.

My four-decade scientific journey started serendipitously (and with a certain degree of ignorance) with glycogen. This molecule brought my interest to glia and astrocytes, later allowing me to reveal the unexpected role of lactate in the brain, with its implications for plasticity, memory, and brain disorders (Finsterwald et al., 2015; Elsayed and Magistretti 2015). In hindsight, it may seem like a logically, quasi-planned sequence of events. But of course it is not: curiosity, chance, and the unexpected made this happen. Maybe the main lesson that I draw is this: keep an open mind and cherish the unexpected.

Selected Bibliography

Allaman I, Pellerin L and Magistretti PJ (2000) Protein targeting to glycogen (PTG) mRNA expression is stimulated by noradrenaline in mouse cortical astrocytes. Glia (4):382–91.

Allaman I, Gavillet M, Bélanger M, Laroche T, Viertl T, Lashuel HA and Magistretti PJ (2010) Amyloid beta-aggregates cause alterations of astrocytic metabolic phenotype: Impact on neuronal viability. J Neurosci 30(9):3326–38.

Ansermet F and Magistretti PJ (2004) A chacun son cerveau: plasticité neuronale et inconscient. Odile Jacob, Paris.

Ansermet F and Magistretti PJ (2010) Les énigmes du plaisir. Odile Jacob, Paris.

Arminjon M, Ansermet F and Magistretti PJ (2010) The homeostatic psyche: Freudian theory and somatic markers. J Physiol Paris 104(5):272–8.

Arminjon M, Ansermet F and Magistretti PJ (2011) Emergence of the cerebral self, from Theodor Meynert to Antonio Damasio. Psychiatr Sci Hum Neurosci 9:153–61.

Bak LK and Walls AB (2018) CrossTalk opposing view: lack of evidence supporting an astrocyte-to-neuron lactate shuttle coupling neuronal activity to glucose utilisation in the brain. J Physiol 596(3):351–53. doi: 10.1113/JP274945. [Epub 2018 Jan 2.]

Barros LF and Weber B (2018) CrossTalk proposal: an important astrocyte-to-neuron lactate shuttle couples neuronal activity to glucose utilisation in the brain. J Physiol 596(3):347–50.

Beaudet A and Descarries L (1978) The monoamine innervation of rat cerebral cortex: synaptic and nonsynaptic axon terminals. Neuroscience 3(10):851–60.

Bélanger M, Allaman I and Magistretti PJ (2011a) Brain energy metabolism: focus on astrocyte-neuron metabolic cooperation. Cell Metab 14(6):724–38.

Bélanger M, Yang J, Petit JM, Laroche T, Magistretti PJ* and Allaman I* (2011b) Role of the glyoxalase system in astrocyte-mediated neuroprotection. J Neurosci 31(50):18338–52.

Berl S, Nicklas WJ and Clarke DD (1968) Compartmentation of glutamic acid metabolism in brain slices. J Neurochem 15:131–40.

Bernardinelli Y, Magistretti PJ and Chatton JY (2004) Astrocytes generate Na+-mediated metabolic waves. Proc Natl Acad Sci USA 101(41):14937–42.

Berthet C, Lei H, Thevenet J, Gruetter R, Magistretti PJ and Hirt L (2009) Neuroprotective role of lactate after cerebral ischemia. J Cereb Blood Flow Metab (11):1780–9.

Berthet C, Castillo X, Magistretti PJ and Hirt L (2012) New evidence of neuroprotection by lactate after transient focal cerebral ischaemia: extended benefit after intracerebroventricular injection and efficacy of intravenous administration. Cerebrovasc Dis 34(5-6):329–35.

Bittar PG, Charnay Y, Pellerin L, Bouras C and Magistretti PJ (1996) Selective distribution of lactate dehydrogenase isoenzymes in neurons and astrocytes of the human brain. J Cereb Blood Flow Metab (6):1079–89.

Bliss TM, Ip M, Cheng E, Minami M, Pellerin L, Magistretti PJ and Sapolsky RM (2004) Dual-gene, dual-cell type therapy against an excitotoxic insult by bolstering neuroenergetics. J Neurosci 24(27):6202–8.

Bloom F, Segal D, Ling N and Guillemin R (1976) Endorphins: profound behavioral effects in rats suggest new etiological factors in mental illness. Science 194(4265):630–2.

Bloom FE (1977) Peptide transmitters: clues to the chemical cryptogram of interneuronal communication? Biosystems (4):179–83.

Bloom FE (2012) The history of neuroscience in autobiography, Volume 7. Edited by Larry R. Squire, 1–56, Oxford University Press.

Boury-Jamot B, Carrard A, Martin JL, Halfon O, Magistretti PJ* and Boutrel B* (2015) Disrupting astrocyte-neuron lactate transfer persistently reduces conditioned responses to cocaine. Mol Psychiatry doi: 10.1038/mp.2015.157. [Epub ahead of print.]

Bouzat P, Magistretti PJ and Oddo M (2014) Hypertonic lactate and the injured brain: facts and the potential for positive clinical implications. Intensive Care Med 40(6):920–1.

Braitenberg V and Schuz A (1998) Cortex: statistics and geometry of neuronal connectivity. Springer, Berlin.

Bröer S, Rahman B, Pellegri G, Pellerin L, Martin JL, Verleysdonk S, Hamprecht B and Magistretti PJ (1997) Comparison of lactate transport in astroglial cells and monocarboxylate transporter 1 (MCT1) expressing Xenopus laevis oocytes. J Biol Chem 272(48):30096–102.

Brooks GA (1986) Lactate production under fully aerobic conditions: the lactate shuttle during rest and exercise. Fed Proc 45(13): 2924–9.

Brooks GA (2018) The science and translation of lactate shuttle. Theory Cell Metab 27(4):757–85.

Bucher MB and Schorderet M (1975) Dopamine- and apomorphine-sensitive adenylate cyclase in homogenates of rabbit retina. Naunyn Schmiedebergs Arch Pharmacol 288(1):103–7.

Burt DR, Enna SJ, Creese I and Snyder SH (1975) Dopamine receptor binding in the corpus striatum of mammalian brain. Proc Natl Acad Sci USA 72(11):4655–9.

Calì C, Agus M, Kare K, Boges DJ, Lehväslaiho H, Hadwiger M and Magistretti PJ (2019) 3D cellular reconstruction of cortical glia and parenchymal morphometric analysis from Serial Block-Face Electron Microscopy of juvenile rat. Prog Neurobiol 183:101696. doi: 10.1016/j.pneurobio.2019.101696. [Epub 2019 Sep 21.]

Calì C, Baghabra J, Boges DJ, Holst GR, Kreshuk A, Hamprecht FA, Srinivasan M, Lehväslaiho H and Magistretti PJ (2016) Three-dimensional immersive virtual reality for studying cellular compartments in 3D models from EM preparations of neural tissues. J Comp Neurol 524(1):23–38.

Cardinaux JR and Magistretti PJ (1996) Vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, and noradrenaline induce the transcription factors CCAAT/enhancer binding protein (C/EBP)-beta and C/EBP delta in mouse cortical astrocytes: involvement in cAMP-regulated glycogen metabolism. J Neurosci 16(3):919–29.

Carrard A, Elsayed M, Margineanu M, Boury-Jamot B, Fragnière L, Meylan EM, Petit JM, Fiumelli H, Magistretti PJ* and Martin JL* (2016) Peripheral administration of lactate produces antidepressant-like effects. Mol Psychiatry doi: 10.1038/mp.2016.237.

Carteron L, Solari D, Patet C, Quintard H, Miroz JP, Bloch J, Daniel RT, Hirt L, Eckert P, Magistretti PJ and Oddo M (2018) Hypertonic lactate to improve cerebral perfusion and glucose availability after acute brain injury. Crit Care Med doi: 10.1097/CCM.0000000000003274. [Epub ahead of print.]

Chavkin C, Bakhit C, Weber E and Bloom FE (1983) Relative contents and concomitant releases of prodynorphin/neoendorphin-derived peptides in rat hippocampus. Proc Natl Acad Sci USA 80(24):7669–73.

Cholet N, Pellerin L, Welker E, Lacombe P, Seylaz J, Magistretti PJ and Bonvento G (2001) Local injection of antisense oligonucleotides targeted to the glial glutamate transporter glast decreases the metabolic response to somatosensory activation. J Cereb Blood Flow Metab 21(4):404–12.

Choi HB, Gordon GR, Zhou N, Tai C, Rungta RL, Martinez J, Milner TA, Ryu JK, McLarnon JG, Tresguerres M, Levin LR, Buck J, MacVicar BA (2012) Metabolic communication between astrocytes and neurons via bicarbonate-responsive soluble adenylyl cyclase. Neuron 75(6):1094–104.

Clement-Cormier YC, Kebabian JW, Petzold GL and Greengard P (1974) Dopamine-sensitive adenylate cyclase in mammalian brain: a possible site of action of antipsychotic drugs. Proc Natl Acad Sci USA 71(4):1113–7.

Coggan JS, Calì C, Keller D, Agus M, Boges D, Abdellah M, Kare K, Lehväslaiho H, Eilemann S, Jolivet RB, Hadwiger M, Markram H, Schürmann F and Magistretti PJ (2018) A process for digitizing and simulating biologically realistic oligocellular networks demonstrated for the neuro-glio-vascular ensemble. Front Neurosci 12:664. doi: 10.3389/fnins.2018.00664. [eCollection 2018.]

Coggan JS, Keller D, Markram H, Schürmann F, Magistretti PJ (2020) Excitation states of metabolic networks predict dose-response fingerprinting and ligand pulse phase signalling. J Theor Biol 487:110123. doi: 10.1016/j.jtbi.2019.110123. [Epub 2019 Dec 19.]

D’Angour A (2013) Love’s battlefield: rethinking Sappho fr 31. In « Erôs in Ancient Greece » Ed Sanders, Chiara Thumiger, Christopher Carey, and Nick Lowe, Editors, Oxford Scholarship Online: May 2013 DOI: 10.1093/acprof:oso/9780199605507.001.0001

Djamgoz MB and Wagner HJ (1992) Localization and function of dopamine in the adult vertebrate retina. Neurochem Int 20(2):139–91.

Elsayed M and Magistretti PJ (2015) A new outlook on mental illnesses: glial involvement beyond the glue. Front Cell Neurosci 9:468.

Enna SJ, Bennett JP Jr, Bylund DB, Creese I, Burt DR, Charness ME, Yamamura HI, Simantov R and Snyder SH (1977) Neurotransmitter receptor binding: regional distribution in human brain. J Neurochem 28(1):233–6.

Falck B, Hillarp N-Å, Thieme G and Torp A (1962) Fluorescence of catecholamines and related compounds condensed with formaldehyde. J Histochem Cytochem 10(3):348–54.

Finsterwald C, Magistretti PJ and Lengacher S (2015) Astrocytes: new targets for the treatment of neurodegenerative diseases. Curr Pharm Des 21(25):3570–81.

Foote SL, Aston-Jones G and Bloom FE (1980) Impulse activity of locus coeruleus neurons in awake rats and monkeys is a function of sensory stimulation and arousal. Proc Natl Acad Sci USA 77(5):3033–7.

Foote SL, Bloom FE and Aston-Jones G (1983) Nucleus locus ceruleus: new evidence of anatomical and physiological specificity. Physiol Rev 63(3):844–914.

Fox PT and Raichle ME (1986) Focal physiological uncoupling of cerebral blood flow and oxidative metabolism during somatosensory stimulation in human subjects. Proc Natl Acad Sci USA 83(4):1140–4.

Fox PT, Raichle ME, Mintun MA and Dence C (1988) Nonoxidative glucose consumption during focal physiologic neural activity. Science 241(4):462–4.

Gao V, Suzuki A, Magistretti PJ, Lengacher S, Pollonini G, Steinman MQ and Alberini CM (2016) Astrocyte β2-adrenergic receptors mediate hippocampal long-term memory consolidation. Proc Natl Acad Sci USA 113(30):8526–31. doi: 10.1073/pnas.1605063113.

Garau L, Govoni S, Stefanini E, Trabucchi M and Spano PF (Oct 1978) Dopamine receptors: pharmacological and anatomical evidences indicate that two distinct dopamine receptor populations are present in rat striatum. Life Sci 23(17–18):1745–50.

Giulietti I (2008) Magistretti e Trefogli, medici chirurghi del ‘700 e ‘800, patrizi di Torricella-Taverne. Storia Medica Ticinese, Taverne.

Greengard P and Straub RW (1959) Effect of frequency of electrical stimulation on the concentration of intermediary metabolites in mammalian non-myelinated fibres. J Physiol 148(2):353–61.

Greengard P and Straub RW (1962) Metabolic studies on the hyperpolarization following activity in mammalian non-myelinated nerve fibres. J Physiol 161:414–23.

Grzanna R, Molliver ME and Coyle JT (1978) Visualization of central noradrenergic neurons in thick sections by the unlabeled antibody method: a transmitter-specific Golgi image. Proc Natl Acad Sci USA 75(5):2502–6.

Hof PR, Pascale E and Magistretti PJ (1988) K+ at concentrations reached in the extracellular space during neuronal activity promotes a Ca++-dependent glycogenolysis. J Neurosci (6):1922–8.

Hof PR, Dietl MM, Charnay Y, Martin JL, Bouras C, Palacios JM and Magistretti PJ (1991) Vasoactive intestinal peptide binding sites and fibers in the brain of the pigeon Columba livia: an autoradiographic and immunohistochemical study. J Comp Neurol 305(3):393–411.

Hoffer BJ, Siggins GR and Bloom FE (1971) Studies on norepinephrine-containing afferents to Purkinje cells of rat cerebellum. II. Sensitivity of Purkinje cells to norepinephrine and related substances administered by microiontophoresis. Brain Res 25(3):523–34.

Hokfelt T, Elfvin LG, Elde R, Schultzberg M, Goldstein M and Luft, R (1977) Occurrence of somatostatin-like immunoreactivity in some peripheral sympathetic noradrenergic neurons. Proc Natl Acad Sci USA 74(8):3587–91.

Hökfelt, T (1991) Neuropeptides in perspective: the last ten years. Neuron 7(6):867–879.

Irace F and Pasca, V (1999) Vico Magistretti: architetto e designer. Electa, Milano.

Itoh Y, Esaki T, Shimoji, K, Cook M, Law MJ, Kaufman E and Sokoloff L (2003) Dichloroacetate effects on glucose and lactate oxidation by neurons and astroglia in vitro and on glucose utilization by brain in vivo. Proc Natl Acad Sci USA 100(8):4879–84.

Jourdain P, Pavillon N, Moratal C, Boss D, Rappaz B, Depeursinge C, Marquet P and Magistretti PJ (2011) determination of transmembrane water fluxes in neurons elicited by glutamate ionotropic receptors and by the cotransporters KCC2 and NKCC1: a digital holographic microscopy study. J Neurosci 31(33):11846–54.

Jourdain P, Allaman I, Rothenfusser K, Fiumelli H, Marquet P and Magistretti PJ (2016) L-Lactate protects neurons against excitotoxicity: implication of an ATP-mediated signaling cascade. Sci Rep 6:21250. doi: 10.1038/srep21250.

Jourdain P, Rothenfusser K, Ben-Adiba C, Allaman I, Marquet P, Magistretti PJ (2018) Dual action of L-Lactate on the activity of NR2B-containing NMDA receptors: from potentiation to neuroprotection. Sci Rep 8(1):13472.

Karnovsky M and Bolis L (1982) Phagocytosis: past and future. Academic Press, New York.

Kebabian JW, Petzold GL and Greengard P (1972) Dopamine-sensitive adenylate cyclase in caudate nucleus of rat brain, and its similarity to the “dopamine receptor.” Proc Natl Acad Sci USA 69(8):2145–9.

Kadekaro M, Crane AM and Sokoloff L (1985) Differential effects of electrical stimulation of sciatic nerve on metabolic activity in spinal cord and dorsal root ganglion in the rat. Proc Natl Acad Sci USA 82(17):6010–13.

Kerr SE (1938) The carbohydrate metabolism of brain: VI isolation of glycogen. J Biol Chem 123:443–9.

Keynes JM (1936) The general theory of employment, interest and money. Volume VII of collected writings, 161–162. Macmillan, London.

Kilic K, Karatas H, Donmez-Demir B, Eren-Kocak E, Gursoy-Ozdemir Y, Can A, Petit JM, Magistretti PJ and Dalkara T (2017) inadequate brain glycogen or sleep increases spreading depression susceptibility. Ann Neurol doi: 10.1002/ana.25122. [Epub ahead of print.]

Laughton J, Charnay Y, Belloir L, Pellerin L, Magistretti PJ and Bouras C (2000) Differential mRNA distribution for lactate dehydrogenase LDH-1 and LDH-5 isoforms in the rat brain. Neuroscience 96(3):619–25.

Locatelli R (2012) Homines loci torrexelle et tabernarum. Patriciato e Comune di Torricella-Taverne.

McAfee DA, Schorderet M and Greengard P (1971) Adenosine 3′,5′-monophosphate in nervous tissue: increase associated with synaptic transmission. Science 171(3976):1156–8.

McIlwain H (1953) Substances which support respiration and metabolic response to electrical impulses in human cerebral tissues. J Neurol Neurosurg Psych 16(4):257–266.

Magistretti PJ (1990) VIP neurons in the cerebral cortex. Trends Pharmacol Sci 11(6):250–4.

Magistretti PJ and Schorderet M (1979) Dopamine receptors in bovine retina: characterization of 3H-spiroperidol binding and its use for screening dopamine receptor affinity of drugs. Life Sci 25(19):1675–86.

Magistretti PJ, Morrison JH, Shoemaker WJ, Sapin V and Bloom FE (1981) Vasoactive intestinal polypeptide induced glycogenolysis in mouse cortical slices: a possible regulatory mechanism for the local control of energy metabolism. Proc Natl Acad Sci USA 78(10):6535–9.

Magistretti PJ, Manthorpe M, Bloom FE and Varon S (1983) Functional receptors for vasoactive intestinal peptide in cultured astroglia from neonatal rat brain. Regul Pept (1):71–80.

Magistretti PJ and Schorderet M (1984) VIP and noradrenaline act synergistically to increase cyclic AMP in cerebral cortex. Nature 308(5956):280–2.

Magistretti PJ and Morrison JH (1985) VIP neurons in the neocortex. Trends Neurosci 8:7–8.

Magistretti PJ and Schorderet M (1985) Norepinephrine and histamine potentiate the increases in cyclic adenosine 3’:5’-monophosphate elicited by vasoactive intestinal polypeptide in mouse cerebral cortical slices: mediation by alpha 1-adrenergic and H1-histaminergic receptors. J Neurosci (2):362–8.

Magistretti PJ, Hof P and Martin JL (1986) Adenosine stimulates glycogenolysis in mouse cerebral cortex: a possible coupling mechanism between neuronal activity and energy metabolism. J Neurosci (9):2558–62.

Magistretti PJ and Morrison JH (1988) Noradrenaline- and vasoactive intestinal peptide-containing neuronal systems in neocortex: functional convergence with contrasting morphology. Neuroscience (2):367–78.

Magistretti PJ and Chatton JY (2005) Relationship between L-glutamate-regulated intracellular (Na (+) dynamics and ATP hydrolysis in astrocytes. J Neural Transm 112(1):77–85.

Magistretti, PJ and Allaman I (2015) A cellular perspective on brain energy metabolism and functional imaging. Neuron 86(4):883–901.

Magistretti PJ and Allaman I (2018) Lactate in the brain: from metabolic end-product to signalling molecule. Nat Rev Neurosci 19(4):235–49. doi: 10.1038/nrn.2018.19.

Margineanu MB, Mahmood H, Fiumelli H and Magistretti PJ (2018) L-lactate regulates the expression of synaptic plasticity and neuroprotection genes in cortical neurons: a transcriptome analysis. Front Mol Neurosci 11:375. doi: 10.3389/fnmol.2018.00375. [eCollection 2018.]

Marquet P, Depeursinge C and Magistretti PJ (2013) Exploring neural cell dynamics with digital holographic microscopy. Annu Rev Biomed Eng 15:407–31.

Martin JL, Dietl MM, Hof PR, Palacios JM and Magistretti PJ (1987) Autoradiographic mapping of [mono (125I) iodo-Tyr10, MetO17]-vasoactive intestinal peptide binding sites in the rat brain. Neuroscience 23(2):539–65.

Martin JL and Magistretti PJ (1989a) Pharmacological studies of voltage-sensitive Ca²⁺-channels involved in the release of vasoactive intestinal peptide evoked by K+ in mouse cerebral cortical slices. Neuroscience 30(2):423–31.

Martin JL and Magistretti PJ (1989b) Release of vasoactive intestinal peptide in mouse cerebral cortex: Evidence for a role of arachidonic acid metabolites. J Neurosci (7):2536–42

Morrison JH, Grzanna R, Molliver ME and Coyle JT (1978) The distribution and orientation of noradrenergic fibers in neocortex of the rat: an immunofluorescence study. J Comp Neurol 181(1):17–39.

Morrison JH, Molliver ME and Grzanna R (1979) Noradrenergic innervation of cerebral cortex: widespread effects of local cortical lesions. Science 205(4403):313–6.

Morrison JH, Molliver ME and Grzanna R and Coyle JT (1981) The intra-cortical trajectory of the coeruleo-cortical projection in the rat: a tangentially organized cortical afferent. Neuroscience 6(2):139–58.

Morrison JH, Benoit R, Magistretti PJ and Bloom FE (1983) Immunohistochemical distribution of pro-somatostatin-related peptides in cerebral cortex. Brain Res 262(2):344–51.

Morrison JH and Magistretti PJ (1983) Monoamines and peptides in cerebral cortex. Trends Neurosci 6:146–15.

Morrison JH, Magistretti PJ, Benoît R and Bloom FE (1984) The distribution and morphological characteristics of the intracortical VIP-positive cell: an immunohistochemical analysis. Brain Res 292(2):269–82.

Morrison BM, Lee Y, Li Y, Lengacher S, Farah MH, Liu Y, Tsingalia A, Jin L, Zhang PW, Griffin JW, Pellerin L, Magistretti PJ and Rothstein JD (2012) Oligodendroglia have a fundamental role in metabolic support of axons and contribute to neurodegeneration. Nature 487(7408):443–8.

Nelson SR, Schulz DW, Passonneau JV and Lowry OH (1968) Control of glycogen levels in brain. J Neurochem (11):1271–9.

Pasca V (1991) Vico Magistretti: designer. Thames & Hudson, London.

Pellerin L and Magistretti PJ (1994) Glutamate uptake into astrocytes stimulates aerobic glycolysis: A mechanism coupling neuronal activity to glucose utilization. Proc Natl Acad Sci USA 91(22):10625–9.

Pellerin L and Magistretti PJ (1997) Glutamate uptake stimulates Na+/K+-ATPase activity in astrocytes via activation of a distinct subunit highly sensitive to ouabain. J Neurochem 69(5):2132–7.

Pellerin L, Pellegri G, Martin JL and Magistretti PJ (1998) Expression of monocarboxylate transporter mRNAs in mouse brain: support for a distinct role of lactate as an energy substrate for the neonatal vs. adult brain. Proc Natl Acad Sci USA 95(7):3990–5.

Pellerin L and Magistretti PJ (2012) Sweet sixteen for ANLS. J Cereb Blood Flow Metab 32(7):1152–66.

Peters A and Kimerer LM (1981) Bipolar neurons in rat visual cortex: a combined Golgi-electron microscope study. J Neurocytol 10(6):921–46.

Petit JM, Gyger J, Burlet-Godinot S, Fiumelli H, Martin JL and Magistretti PJ (2013) Genes involved in the astrocyte-neuron lactate shuttle (ANLS) are specifically regulated in cortical astrocytes following sleep deprivation in mice. Sleep 36(10):1445–58.

Petit JM and Magistretti PJ (2015) Regulation of neuron-astrocyte metabolic coupling across the sleep-wake cycle. Neuroscience pii: S0306-4522(15)01090-8.

Phelps CH (1972) Barbiturate-induced glycogen accumulation in brain. An electron microscopic study. Brain Res 39(1):225–34.

Pierre K, Pellerin L, Debernardi R, Riederer BM and Magistretti PJ (2000) Cell-specific localization of monocarboxylate transporters, MCT1 and MCT2 in the adult mouse brain revealed by double immunohistochemical labeling and confocal microscopy. Neuroscience 100(3):617–27.

Pittman QJ and Siggins GR (1981) Somatostatin hyperpolarizes hippocampal pyramidal cells in vitro. Brain Res 221(2):402–8.

Pliteri S (2003) Il pancreas esocrino. Masson & Cie, Paris.

Pliteri S and Sironi, PG (2005) Storia di un chirurgo clinico. M&B Publishers, Milano.

Quach TT, Rose C and Schwartz JC (1978) [3H]Glycogen hydrolysis in brain slices: responses to neurotransmitters and modulation of noradrenaline receptors. J Neurochem (6):1335–41.

Quik M, Iversen LL and Bloom SR (1978) Effect of vasoactive intestinal peptide (VIP) and other peptides on cAMP accumulation in rat brain. Biochem Pharmacol 27(18):2209–13.

Rall TW and Sutherland EW (1958) Formation of a cyclic adenine ribonucleotide by tissue particles. J Biol Chem 232(2):1065–76.

Ruminot I, Gutierrez R, Pena-Munzenmayer, G., Anazco, C, Sotelo-Hitschfeld, T, Lerchundi, R, Niemeyer MI, Shull GE and Barros LF (2011) NBCe1 mediates the acute stimulation of astrocytic glycolysis by extracellular K+. J Neurosci 31(4):14264–71.

Schaad N, Schorderet M and Magistretti PJ (1987) Synergism between VIP and noradrenaline in increasing cAMP in the cerebral cortex: role of prostaglandins. Nature 328(6131):637–40.

Siggins GR, Oliver AP, Hoffer BJ and Bloom FE (1971) Cyclic adenosine monophosphate and norepinephrine: effects on transmembrane properties of cerebellar Purkinje cells. Science 171(3967):192–4.

Siggins GR, McGinty JF, Morrison JH, Pittman QJ, Zieglgänsberger W, Magistretti PJ and Gruol DL (1982) The role of neuropeptides in the hippocampal formation. Adv Biochem Psychopharmacol 33:413–22.

Siggins GR, Henriksen SJ, Chavkin C and Gruol D (1986) Opioid peptides and epileptogenesis in the limbic system: cellular mechanisms. Adv Neurol 44:501–12.

Sokoloff L, Reivich M, Kennedy C, Des Rosiers MH, Patlak CS, Pettigrew KD, Sakurada O and Shinohara M (1977) The [14C]deoxyglucose method for the measurement of local cerebral glucose utilization: theory, procedure, and normal values in the conscious and anesthetized albino rat. J Neurochem 28(5):897–916.

Sokoloff L (1981) Localization of functional activity in the central nervous system by measurement of glucose utilization with radioactive deoxyglucose. J Cereb Blood Flow Metab 1(1):7–36.

Sotelo C and Palay SL (1968) The fine structure of the lateral vestibular nucleus in the rat: I. Neurons and neuroglial cells. J Cell Biol 36(1):151–79.

Sutherland EW and Robison GA (1966) The role of cyclic-3’,5’-AMP in responses to catecholamines and other hormones. Pharmacol Rev 18(1):145–64.

Suzuki A, Stern SA, Bozdagi O, Huntley GW, Walker RH, Magistretti PJ and Alberini CM (2011) Astrocyte-neuron lactate transport is required for long-term memory formation. Cell 144(5):810–23.

Swanson RA, Morton MM, Sagar SM, Sharp FR (1992) Sensory stimulation induces local cerebral glycogenolysis: demonstration by autoradiography. Neuroscience 51:451–61.

Tadi M, Allaman I, Lengacher S, Grenningloh G and Magistretti PJ (2015) Learning-induced gene expression in the hippocampus reveals a role of neuron–astrocyte metabolic coupling in long term memory. PLoS One 10(10):e0141568.

Takahashi S, Driscoll BF, Law MJ and Sokoloff L (1995) Role of sodium and potassium ions in regulation of glucose metabolism in cultured astroglia. Proc Natl Acad Sci USA 92(10):4616–20.

Tauffenberger A, Fiumelli H, Almustafa S and Magistretti PJ (2019) Lactate and pyruvate promote oxidative stress resistance through hormetic ROS signaling. Cell Death Dis 10(9):653.

Tran The J, Magistretti P and Ansermet F (2018) The epistemological foundations of Freud’s energetics model. Front Psychol 9:1861. doi: 10.3389/fpsyg.2018.01861. [eCollection 2018.]

Vezzoli E, Calì C, De Roo M, Ponzoni L, Sogne E, Gagnon N, Francolini M, Braida D, Sala M, Muller D, Falqui A and Magistretti PJ (2019) Ultrastructural evidence for a role of astrocytes and glycogen-derived lactate in learning-dependent synaptic stabilization. Cereb Cortex 6. pii: bhz226. doi: 10.1093/cercor/bhz226. [Epub ahead of print.]

Voutsinos-Porche B, Bonvento G, Tanaka K, Steiner P, Welker E, Chatton JA, Magistretti PJ and Pellerin L (2003) Glial glutamate transporters mediate a functional metabolic crosstalk between neurons and astrocytes in the mouse developing cortex. Neuron 37(2):275–86.

Warburg O (1956) On the origin of cancer cells. Science 123(3191):309–14.

Weber B and Barros LF (2015) The astrocyte: powerhouse and recycling center. Cold Spring Harb Perspect Biol 7(12):a020396.

Yang J, Ruchti E, Petit JM, Jourdain P, Grenningloh G, Allaman I and Magistretti PJ (2014) Lactate promotes plasticity gene expression by potentiating NMDA signaling in neurons. Proc Natl Acad Sci USA 111(33):12228–33.

Yu N, Martin JL, Stella N and Magistretti PJ (1993) Arachidonic acid stimulates glucose uptake in cerebral cortical astrocytes. Proc Natl Acad Sci USA 90(9):4042–6.

¹Pier Giulio Magistretti, https://it.wikipedia.org/wiki/Pier_Giulio_Magistretti.

²Fondzaione Vico Magistretti, V1CO: 1920/2020 Magistretti [digital archive], http://www.vicomagistretti.it/en/.

Yasushi Miyashita

BORN:

Tokyo, Japan

December 8, 1949

EDUCATION:

The University of Tokyo, BS (1972)

The University of Tokyo, PhD (1978)

APPOINTMENTS:

Assistant Professor, The University of Tokyo School of Medicine (1978–1983)

University Lecturer, The University of Tokyo School of Medicine (1983–1989)

Visiting Lecturer, University of Oxford, UK (1984–1985)

Professor, The University of Tokyo School of Medicine (1989–2015)

Professor, The University of Tokyo Graduate School of Science (1996–2013)

Professor, National Institute for Physiological Sciences (1996–2002)

Professor, Juntendo University Graduate School of Medicine (2015–present)

Team Leader, RIKEN Center for Brain Science (2018–present)

Director, RIKEN Center for Brain Science (2018–present)

HONORS AND AWARDS (SELECTED)

Tsukahara Prize, Brain Science Foundation (1992)

Plenary Lecture, International Congress of Neuroethology (2001)

Keynote Lecture, Organization for Human Brain Mapping (2001)

Keio Medical Science Prize, Keio Medical Science Foundation (2003)

Presidential Lecture, International Brain Research Organization (2003)

Asahi Prize, Asahi Cultural Foundation (2004)

EBBS lecture, Federation of European Neurosciences Societies (2004)

Medal with Purple Ribbon, Cabinet Office, Government of Japan (2004)

Presidential Special Lecture, Society for Neuroscience Annual Meeting (2005)

Japan Academy Prize, Japan Academy of Science (2007)

Fujiwara Prize, The Fujiwara Foundation of Science (2013)

Plenary Lecture, International Union of Physiological Sciences (2017)

Yasushi Miyashita has been studying the memory and metamemory system in primates to reveal the dynamics of the cortical global networks and local circuits that underlie the memory of objects. He has made three major discoveries: first, the memory neurons that encode and retrieve associative long-term memory of objects in the temporal cortex; second, the top-down signal from the prefrontal cortex to the memory neurons in the temporal cortex for memory retrieval; and third, the metamemory centers in the frontopolar and anterior dorsolateral prefrontal cortex that interact with the temporal lobe memory centers. These discoveries clarify where and how mnemonic representations are organized in the primate brain and which mechanism underlies the on-demand reactivation of the representation during voluntary recall. His work also provides mechanistic insight into the long-standing question of how we comprehend the meaning of what we see. Finally, his recent work on metamemory has enriched our understanding of how our metacognition (cognition of cognition) is implemented in the brain and how retrospection becomes possible.

Yasushi Miyashita

Early Life and Education: Mathematical Beauty or a Mystery of the Human Mind?

I was born in 1949 in Ochanomizu, Tokyo, 1 km from both the Imperial Palace and the University of Tokyo. I grew up in a part of Shinjuku that is now about 1.5 km from the current Tokyo Metropolitan Government Building. But when I was a child, there were still wooded leafy parks and playgrounds here and there in the area. My parents were schoolteachers who specialized in humanities. Before I went to kindergarten, while my parents were at work during the daytime, I went to the grounds of a shrine and temple with an elderly couple who took care of me. There, I enjoyed running around with a white mixed-breed dog. Once I started going to elementary school, I would also spend time in my father’s library, where I enjoyed looking at the illustrations and artwork in the books. Although I forgot most of them by the time I grew up, one exception was Hyakunin Isshu, a classical Japanese anthology of 100 poems by 100 different poets. This traditional Japanese anthology also served as the basis of a card game consisting of 100 pairs of a poem card and a picture card, which my family and I enjoyed playing, particularly while on New Year’s holidays. In later years, as I organized my father’s books after he passed away, I found myself remembering some of the artwork in the books from such poets as Rimbaud and Verlaine in Japanese translation. In particular, I had clear memories of Aubrey Beardsley’s artwork in Salomé by Oscar Wilde. The experiences of individuals during their childhood remain deep in memory. In my case, for example, you can sometimes see motifs from Salomé that I borrowed for the opening line in my presentation slides for a scientific meeting.

In upper-elementary grades, I diligently practiced swimming to become the school’s representative at the regional tournament. In the process, I learned that I had no talent for swimming. Around that time, I started spending less time with my father’s books and instead went to a nearby public library, where I read George Gamow’s books from cover to cover. As with other books, earlier in my life, I was initially attracted by the artwork, but once I started to read them, I became absorbed by the content of Mr. Tompkins in Wonderland and One Two Three . . . Infinity. I consider myself fortunate to have been fascinated by the mysteries of special relativity theory (depicted in Mr. Tompkins in Wonderland) and infinite set theory (depicted in One Two Three . . . Infinity), particularly the concept of cardinal numbers, during my younger years. I still feel some emotion when I encounter a logic problem or discussion that uses the diagonal argument that I first learned when Gamow demonstrated the difference between two sets with different cardinal numbers (e.g., ₀ and ₁). During junior high school, I dedicated myself not to swimming but to gymnastics, particularly the horizontal bar. As with swimming, I ended up learning that I had no talent for gymnastics. At the same time, however, I was attending extracurricular classes in German and French, for the simple reason that I wanted to sing songs by Schubert and Édith Piaf. Moreover, NHK (Nippon Hoso Kyokai; the Japan Broadcasting Corporation) Radio had started offering German and French courses, which I also took. NHK currently offers television and radio courses in Chinese, Korean, Italian, Spanish, Russian, Arabic, and Portuguese, which would have attracted me if available at that time. During junior high and high school, I read basically everything I could get my hands on, but I sometimes was attracted by more academic books. The 12 volumes of Vladimir Smirnov’s A Course of Higher Mathematics: Advanced Calculus had already been published in Japanese translation and were easy to read, so I held a reading club with my friends to read some of the volumes, such as the one on partial differential equations and the Hilbert space. At the same time, I held a journal club with other friends on Maurice Merleau-Ponty to learn stylish French by referring to a Japanese translation of La Structure du comportement (The Structure of Behavior) and Phénoménologie de la perception (Phenomenology of Perception). Although I was not convinced of all the arguments therein, my basic awareness of issues raised by these books may have determined the direction of my life.

At the time that I was considering enrollment in a university, I had not yet made up my mind about the future direction I would take. Although one of my high school teachers recommended that I enter law school to become a lawyer or statesman, I vaguely imagined myself working in academia. But lacking sufficient direction to imagine a specific theme of my life’s work in academia, I vacillated between the physical beauty of the world’s order, which I felt could be mathematically expressed, and the mysteries of the human mind, as described by poets and philosophers. At the end, I decided to study physics at the University of Tokyo as an undergraduate student.

After entering university, I continued to be uncertain about a course of study. However, the civil unrest of Mai 68 in France and the global anti–Vietnam War movement in the United States triggered a university-wide strike at the University of Tokyo, which provided me with time to consider my options. I tried my hand at everything from Bourbaki’s Éléments de mathématique series to cultural anthropology and sociology; my favorites were Max Weber, Karl Mannheim, and Talcott Parsons. I have especially strong memories of tutorials in a student-initiated voluntary course given during the strike by Professor Shozo Omori, a professor at the University of Tokyo and a renowned phenomenologist and philosopher. In an introductory seminar for students working in science, he discussed the philosophical foundation of natural science, based mainly on The Logic of Scientific Discovery by Sir Karl Raimund Popper. In fact, for more than 20 years, until I became a professor at the University of Tokyo School of Medicine in 1989, whenever possible, I participated in the annual meetings of the phenomenology and modern hermeneutics seminar conducted by Professor Yoshihiro Nitta of Toyo University. In later years, I had opportunities to work with Dr. Kei-ichi Noe, who was a colleague in this seminar and later became a leading Japanese philosopher. We co-organized symposia and lectures at the Science Council of Japan, exploring the points of contact between philosophy and natural science.

My wish to find a way to study the mysteries of the human mind using a clear natural scientific method was the basso continuo of my adolescence. I will never forget the impact of reading the chapter entitled “Neuronal Circuit” in A Course of Biophysics (Yoshioka Shoten, 1966), written by Professor Masao Ito, for the first time during high school. This introduction to the concept of the “Neuronal Circuit” strongly shook my heart. Before that, I could not imagine how I could reach the worlds of The Structure of Behavior and Phenomenology of Perception, given the properties of neurons and synapses generally presented in textbooks and popular books explaining the molecular, subcellular, and cellular properties of neurons in the brain. Reading that chapter made me an Ito fan, and I read his books written for the general public immediately after they were published. These included Physiology of Neurons, which was first serialized in the monthly journal KAGAKU (Science) published by Iwanami Shoten and later published as a book entitled Neuron no Seirigaku (Physiology of Neurons, 1972), in which more than one-third of the chapters were devoted to conceptualization and methodological discussion of neuronal circuit analysis. Eventually, I visited Professor Ito, who at the time was an associate professor in the Department of Physiology II at the University of Tokyo School of Medicine, to consult with him about my future career. I was not greatly interested in clinical medicine, which I thought evolved through the accumulation of practical knowledge and practice, and was less directed toward structured theorization and a systematic worldview. Nevertheless, I considered it fine to be enrolled in the Medical School (I was qualified according to university rules) if enrollment provided me with an option to conduct brain research. However, Professor Ito advised me to conduct physiological research under his supervision after I established an academic foundation in the Department of Physics. He kindly introduced me to Professor Setsuro Ebashi, another great physiologist and molecular biologist whom I respected. He had discovered troponin and had elucidated the roles of calcium in muscular contraction. Professor Ebashi’s advice to me was the same as that of Professor Ito.

Ultimately, I decided to pursue my training as a vocational researcher in three steps: training in physics and mathematics during my undergraduate studies, training in physiology in my graduate studies, and training in psychology during my postdoctoral fellowship. In Japanese, it can be expressed that physics explores the kotowari (essence) of the physical world, physiology the kotowari of the biological world and its functionality, and psychology the kotowari of the inner world and mind. I therefore decided to pursue my training in all three kotowaris (i.e., of the physical world, of the biological world, and of the inner world and mind). At that time, however, I was uncertain about how I would be able to develop my own academic field after these educational experiences.

The Ito Laboratory

I could hardly wait to study in Professor Masao Ito’s laboratory. Of course, I enjoyed my physics studies as an undergraduate student. Like many of my classmates, I was absorbed by quantum field theory, particularly gauge theory and second quantization. However, unlike many physicists who were interested in biological phenomena, I did not believe that quantum statistical mechanics, which derive many important macroscopic physical rules from interactions among simpler elements, had the potential to provide a basic understanding of neural circuit dynamics through interactions among neurons and, ultimately, reach the world of The Structure of Behavior.

I started my graduate studies in the Ito laboratory in 1974. When I first met Masao, he was an associate professor at the University of Tokyo School of Medicine, and his laboratory was on the second floor of the School of Medicine Building 1. By 1974, he had already become a full professor, his laboratory had moved to the third floor of the same building, and many researchers from around the world were working in his laboratory. Those whom I directly met included Drs. S. M. Highstein, J. I. Simpson, B. Ghelarducci, M. Dufosse, P. J. Jastreboff, C. Batini, I. Orlov, R. T. Kado, C. D. Balaban, P. Tongroach, V. Chan-Palay, L. Karachot, and T. K. Hensch. Among them, Steve Highstein (1939–2014) later became a professor at Washington University School of Medicine in St. Louis, Missouri, after his residency in the Department of Neurology at Mt. Sinai Hospital in New York. Although Steve conducted his research mainly at Washington University, he often spent the summer at the Marine Biological Laboratories in Woods Hole, Massachusetts. This gave me the opportunity to enjoy yachting with him at Woods Hole, which remains a pleasant memory of my student days.

Professor Ito promoted the internationalization of Japanese neuroscience in various ways. As part of his efforts, he organized a number of international workshops to which Japanese and international researchers were invited. In August 1975, while still a student, I attended an international workshop held at a famous summer resort in Japan, Nikko, where I listened for the first time to presentations and discussions by leading women researchers, including Drs. Ann Graybiel and Victoria Chan-Palay. The experience made a strong impression on me, as did Masao’s determination to promote internationalization and diversity.

Within the Ito laboratory, Associate Professor Keisuke Toyama was responsible for educating the graduate students through journal clubs and seminars. Journal club took place at lunchtime every day, and a meeting to discuss our progress was held every Monday. In the journal club, laboratory members introduced a wide variety of topics covering many different biological fields in English. In addition to these activities, Professor Toyama let us take turns reading a variety of books, including Man on His Nature, 2nd edition (1951) by Sir Charles S. Sherrington, Receptors and Sensory Perception (1955) by Dr. Ragnar Granit, and The Organization of Behavior (1949) by Dr. Donald Hebb. Through these books, the thoughts of these legends in the history of neuroscience deeply affected my later research.

In the Ito laboratory, I devoted myself to studying the function of the cerebellar flocculus, a phylogenetically old area in the cerebellum, in the adaptive control of the vestibulo-ocular reflex. Professor Ito was an advocate of the theoretical hypothesis in systems neuroscience stating that the cerebellum is a “learning machine” responsible for motor learning (Ito, 1970, 1984). This hypothesis is now called the Marr-Albus-Ito model of the cerebellum (Marr, 1969; Ito, 2006). This theory provides the basis for a comprehensive understanding of the functions of the cerebellum, including both the phylogenetically old vestibulo-cerebellum and the phylogenetically newer neocerebellum, which is the part of the cerebellar hemisphere that has evolved the most in humans. To experimentally verify this comprehensive theory, Professor Ito selected the vestibulo-cerebellum, whose anatomical input-output connectivity has been well analyzed and is known to control a simple motor circuit, the tri-synaptic arc of the vestibulo-ocular reflex. This research strategy impressed me a lot.

In daily experiments, I was responsible for a project aimed at elucidating the role of the inferior olive. The core concept of the Marr-Albus-Ito theory is that input from the inferior olive to the cerebellum supplies an error signal that modifies the activity of the cerebellum as a learning machine (Ito, 1974). My mission in this project was to collect experimental evidence addressing this core concept. I sought to accomplish my mission using two approaches. One approach was to record the activity of Purkinje cells to elucidate how inferior olivary input affects the dynamics of the local network within the cerebellum. The other was to use lesioning to obtain causal evidence of the role of inferior olivary input. In later years, the two-pronged strategy of that project would significantly affect my own research strategy toward the elucidation of higher brain function.

Purkinje cells, the only output cells in the cerebellum, receive input from two sources: climbing fibers and mossy fiber-granule cell-parallel fibers. Climbing fibers originate in the inferior olive and directly input to Purkinje cells. In the experiment, we simultaneously recorded both climbing fiber-derived neural firing (complex spikes) and parallel fiber-derived neural firing (simple spikes) in Purkinje cells, and we analyzed how complex and simple spikes change over time along with the progression of adaptive changes in the vestibulo-ocular reflex at the behavioral level (Dufosse et al., 1978; Masao arranged the author names of a paper in alphabetical order). We then investigated whether the observed changes were consistent with the patterns of change theoretically predicted by the Marr-Albus-Ito model. The results of the experiment were quite consistent with the theoretical prediction (Ito et al., 1979). This experience again had a strong impact on my view of the role of theory in systems neuroscience.

In addition to recording single-cell activity for analysis of local network dynamics, I eagerly committed to a lesion experiment. At that time, neither optogenetic techniques, such as the use of ArchT, nor pharmacological neural inhibition techniques with muscimol, both of which we use frequently now (Miyamoto et al., 2017, 2018; Setsuie et al., 2020), were available to inhibit neuronal activities. Therefore, electrocoagulation was the only choice for lesioning a brainstem nucleus. However, the inferior olive is surrounded by a large number of nuclei within the brainstem that are essential for life. Consequently, when using electrocoagulation to destroy the inferior olive or cut the visual input fibers running from the pretectum to the inferior olive, even a slight inaccuracy in the targeting threatens the life of the animal. It was an extremely difficult experiment. Eventually, we reached a conclusion. Both the destruction of the inferior olive and the cutting of the visual input from the pretectum to the inferior olive led to the loss of adaptability of the vestibulo-ocular reflex (Ito and Miyashita, 1975; Miyashita et al., 1980), which provided experimental support for the Marr-Albus-Ito model of the cerebellum.

My experience in the Ito laboratory deeply affected my later research. It was there that I realized the power of empirical studies of brain function. I was convinced that, in principle, it should be possible to approach the world described in The Structure of Behavior, starting with studies of individual neuron activities and network dynamics. Although I had not understood at that time the great distance between “in principle” and “actual” understanding, this experience led me to select systems neuroscience as the field in which I would conduct my life’s work. It was also in the Ito laboratory that I became aware of the importance of both correlational approaches, such as recording single-cell activity, and causal approaches, such as lesion experiments, and their complementarity in empirical studies of brain function. This led me to apply a combination of correlational and causal approaches at various phases of my later research. In addition, I had come to believe that to acquire an understanding of a large research target, such as the motor learning function of the cerebellum, I should focus on elucidating the mechanism of a model (or “prototype”) system that includes the simplest function among those implemented in the target system. Later in life, I thoroughly investigated the simplest model or paradigm (i.e., prototype model) every time I started to study a new higher brain function. An example of the simplest model I chose for the neurophysiological study of declarative (or explicit) memory was the “pair-association memory” paradigm (Sakai and Miyashita, 1991; Miyashita, 2004, 2019), in which I considered the associative nature of long-term memory to be highlighted in its simplest form. Using the same principle, I chose and developed the feeling-of-knowing (FOK) paradigm (Kikyo et al., 2002; Miyashita, 2004) and postdecision wagering confidence paradigm for metamemory (Miyamoto et al., 2017; Miyashita, 2019) for my neurophysiological studies in systems neuroscience. I could not have developed these paradigms for neurophysiology without my experiences in the Ito laboratory. Finally, it was there that I learned the importance and difficulty of presenting and publishing highly original new findings at a high level of international visibility. Masao fought a lot of battles against his competitors at conferences and through publications. In the battles around the cerebellar learning theory and the discovery of the long-term depression of cerebellar Purkinje cell synapses (with which I was not involved), he won the most important ones, but it took many years.

By 1980, Professor Ito’s scientific interest had shifted to long-term depression of cerebellar Purkinje cell synapses. I understood the importance of this phenomenon well, as it was the last piece of the hypothetical elements in the Marr-Albus-Ito model of the cerebellum. However, the time had come for me to leave Masao and to start my own research program. I had already decided on the general direction of my future research: I wanted to explore the human inner world, tapping into the world described in Phenomenology of Perception. But I knew that I had not yet received sufficient training in psychology to do so. Accordingly, I wondered where I should train myself while working as a postdoc. The laboratories of Drs. Evarts and Wurtz at the U.S. National Institutes of Health (NIH) were options I considered first. I respected Drs. Ed Evarts and Bob Wurtz as great pioneers who were running cutting-edge laboratories using monkeys. In 1983, I had an opportunity to visit NIH, where Mickey Goldberg and Oki Hikosaka kindly welcomed me. I was deeply impressed by Mickey’s proud words, “My lab is the best small lab in the world. Smallest and best!” Since then, Drs. Goldberg and Hikosaka have become my best friends in the primate physiology community. However, the studies being conducted in the laboratories of Drs. Evarts and Wurtz were already too firmly established for me; I wanted to conduct my investigations in a less mature field, where I was free to find a new research target of my own. Motor control of the upper limbs or the oculomotor control had already been developed as complete model systems in primate physiology and thus awaited thorough physiological investigation. What I needed was basic training in psychological thinking and experimentation. I sought the opportunity to obtain such training in the Department of Experimental Psychology at University of Oxford. But one of the subliminal reasons I decided to go to Oxford may have been my longing for the origin of neuroscience, which was traceable back from Masao Ito, to Sir John C. Eccles, and finally to Sir Charles Sherrington.

Department of Experimental Psychology at Oxford

In April 1984, I became a visiting lecturer in the Department of Experimental Psychology at University of Oxford. My wife Naomi and I initially lived at Halifax House on South Parks Road, a guesthouse for the university at that time, until we found a terraced house in Cunliffe Close facing Banbury Road. We enjoyed our life in Halifax House, although I made a mistake at the very start. It was Easter Monday when I went for the first time to the Experimental Psychology/Zoology Building (i.e., Tinbergen Building) on South Parks Road; of course, it was closed. Noticing I was in trouble, a bearded gentleman helped me enter the building through a side entrance. This was the first time I met Professor Larry Weiskrantz. I am ashamed to say that I did not know that this gentleman was the head of the Department of Experimental Psychology and a discoverer of blind sight.

I enjoyed my life in the Department of Experimental Psychology. At afternoon teatimes, I very much enjoyed talking with the other researchers, which included legendary pioneers, such as Professors Larry Weiskrantz and Donald Broadbent, as well as young up-and-coming researchers of the time, such as Dr. Dick Passingham. However, this was only possible when my experiment was going well and I could join them at 4 p.m. I did not initially develop a rapport with Jon Driver, because he seemed to be difficult; that is, until our departmental Christmas party, where he showed up wearing a stuffed bunny on his waist, and I finally could have a sort of chat with him, a distant memory for me.

I learned a lot at the Department of Experimental Psychology. I was fortunate enough to receive training in behavioral testing in monkeys from Professor Alan Cowey, in lesion experiments from Dr. David Gaffan, and in neurophysiology from Dr. Ed Rolls. Chantal Stern and Mike Hasselmo, who are currently at Boston University, were graduate students working on the same floor as me and gave me a lot of practical tips for experiments. Dr. Gaffan taught me some fundamental principles and know-how for monkey experiments, which I had previously lacked. I learned from him that, in designing experimental behavior tasks, it’s crucial to maximize monkeys’ spontaneous behavior by taking their ecology into account and to measure their behavior as quantitatively as possible using advanced information technology devices. For example, David and Ed took leadership roles in employing touch panels in the laboratory more than 20 years before the iPhone was equipped with such an interface. My interaction with David continued after I returned to the University of Tokyo. I have a pleasant memory of a dinner at David’s home, with Drs. Mort Mishkin and Betsy Murray, when I visited Oxford University again in 1994. At the EBBS Symposium to mark David’s retirement held in Queen’s College, Oxford in 2011, I had the opportunity to catch up with old friends, including Drs. Mark Buckley, Madeline Eacott, and John Duncan, and to get acquainted with rising stars such as Dr. Mathew Rushworth. Although I learned a lot in the Department of Experimental Psychology, my background at that time limited the experiments that I could contribute to at Oxford and ultimately get published, to those related to neurophysiology. I owe most of my publications during this period to the supervision of Dr. Rolls (Miyashita et al., 1989).

Discovery of Memory Neurons in Tokyo

Discovery of Pictorial Short-Term Memory Neurons

In 1985, I returned to the University of Tokyo School of Medicine, where I took a position as a university lecturer and launched my monkey laboratory. I started my journey from a small corner of the Department of Physiology, with only two Japanese macaque monkeys (Macaca fuscata) and one DEC PDP11 computer. As my goal, I borrowed the phrase “My lab is the best small lab in the world,” which I had heard from Micky Goldberg a few years before, and I worked like a horse. Because the experiment control software programs that are now commercially available from many companies had not yet been developed, I wrote an assembler program for the PDP11 (and later for the VAX11) with functions related to experimental sequence control, video display control, monkey behavior control, and recording time series of spike firing.

Then, I had to ask: what’s the target of study? After wavering, I decided to search for neurons responsible for visual memory in the visual association area in the monkey temporal cortex. I had rationales. My experiences at Oxford made me aware of the depth of the study of memory. Pioneers in the physiology in memory, including Professors John O’Keefe and Tim Bliss, tended to select the hippocampus as their target area of study, with good reason. I asked myself, “What should I select, particularly considering a linkage with general cognition?” I repeatedly read the papers of Professor Brenda Milner (e.g., Scoville and Milner, 1957; Milner, 1968, 1972) and had become convinced that the cortical association areas, rather than the hippocampus, should be studied to explore the seats in the brain that are related to ultimate storage of long-term memory as well as the dynamic expression of short-term and working memory. This belief mostly arose from the fact that, in patient H.M., the retrograde amnesia was relatively mild, or sometimes absent, despite severe anterograde amnesia (Scoville and Milner, 1957; Milner, 1968; Squire et al., 1975; Squire and Wixted, 2011). Then, which cortical association area should I study? Visual research was the major battlefield on which the largest number of excellent researchers were competing across the world. I therefore wanted to compete in that field. In addition, I was familiar with the field of visual research. When I was a graduate student, Dr. Keisuke Toyama, an associate professor in the Ito laboratory, was a physiologist recording neuronal activities in the primary visual cortex of cats. Professor Toyama encouraged us to read the classic papers on visual physiology, including those written by Drs. Hubel and Wiesel, as well as articles and reviews on neuronal activities in the inferior temporal cortex written by Dr. Charles Gross (Gross et al., 1969, 1972) who was one of my heroes. Moreover, I was a long-term follower of Dr. David Marr, starting from the monumental paper on his model of the cerebellar cortex (Marr, 1969), to many MIT AI MEMOs for computer vision and related papers (Marr, 1976, 1980; Marr and Poggio, 1979), and finally to his book VISION (Marr, 1982).

I then had to design a specific experiment. I wanted to use monkeys as subjects and to have them perform tasks that enabled me to make quantitative measurements under conditions in which their behavior could be controlled as rigorously as possible. Ultimately, I decided to start with a delayed matching-to-sample (DMS) task. The DMS task is a form of conditional discrimination and is quite popular for studying learning and memory in animals. During the task, a trial is begun by presenting the subject with a stimulus (a visual object in a visual task), the “sample” stimulus, which the subject is required to remember. The subject is then required to identify from a subsequent set of stimuli, the “choice” stimuli, one that “matches” the sample. In my laboratory, I placed a computer-controlled video display with a transparent touch pad in front of each monkey to rigorously control the presentation of visual stimuli and the monkey’s responses (although quite popular now, it was a unique setup in the mid-1980s). I wanted to set the duration of presentation of each visual stimulus in each trial to be as short as possible. I also wanted to set the delay time to be as long as possible. Delay time, the duration of the period between the sample and choice stimuli, during which nothing except a fixation spot is displayed on the screen, is a key factor in memory load. The two Japanese macaques, Tami and Chie, were great! (By the way, “ta” and “chi” are adjacent phonemes in the Japanese language.) Both monkeys were cooperative in the experiments and performed hundreds of trials each day. I worked to maintain their motivation by preparing their favorite foods (bananas, potatoes, and raisins) in the laboratory. In this way, I started my experiments on the physiology of memory using a DMS task with 0.2 seconds of visual stimulus presentation and 16 seconds of delay time.

During my basic training at Oxford, I learned the importance of controlling the sample size of stimuli—that is, the differential impact on behavioral testing with a small stimulus set and that with a large stimulus set (e.g., see a later paper by Eacott et al., 1994). Initially, I considered using many pictorial stimuli that could serve as trial-unique stimuli. These stimuli needed to be eye-catching to attract the interest of the monkeys. Through trial and error, I created fractal patterns utilizing a fractal algorithm, which enabled me to produce countless different visual graphics using a small number of parameters (Miyashita et al., 1991). This in turn enabled me to design an experiment in which trial-unique graphic stimuli were used in DMS tasks.

From 1985 to 1986, I immersed myself in experiments, devoting myself to recording single-neuron activity using microelectrodes from morning to evening, every day. I worked with Han Soo Chang, a neurosurgeon in the Department of Neurosurgery at the University of Tokyo Hospital, who was studying as a graduate student in the Department of Physiology. In the Ito laboratory, as in many other electrophysiology laboratories around the world, electrical signals reflecting spike firing obtained with microelectrodes were monitored as audio signals that were output from speakers after being amplified and input into a computer. Every day, we concentrated on the sounds of spike firing coming from speakers while monitoring the behavior of the monkeys.

Then, one day in 1986, I heard a series of consecutive strong spike firing sounds that continued for 16 seconds. It was so sudden that I was not sure what had happened. The strong sounds of spike firing occurred only once and never again during the succeeding trials for more than 10 minutes. Nonetheless, I was certain the sounds reflected highly specific spike firing. The sound must have been produced when the neuron fired strongly in response to a particular picture during the recording; I could not think of another reason for the sound. Therefore, although it was unusual, I had no choice but to repeatedly show that particular picture to the monkey to reproduce this phenomenon. I quickly re-wrote the PDP11 software to repeatedly show a particular picture every 10, 20, or 30 trials. The main concern was that the neuron being recorded would move away from the tip of the electrode while I was rewriting the program. Thirty minutes later, I conducted the test again, and the strong consecutive spike sounds returned. I was convinced that there were neurons in the inferior temporal cortex that strongly responded only to a particular picture and continued firing during the 16-second delay time after the picture disappeared from the screen.

Subsequently, however, it was not easy to reproduce this finding. There was no way to predict which neuron would respond to what picture, and most neurons did not respond to any of the pictures tested (rigorously speaking, most neurons responded to some or several stimuli, but only with much weaker firing than the strong firing that I found on the “discovery day.” I was convinced that those weaker firings represent “suboptimal” responses of the neuron, just like the “suboptimal” responses seen in the earlier visual areas). I was a skilled electrophysiologist and had a technique for keeping each single neuron at the tip of an electrode for an hour or even longer, but throughout that hour or so, during which I tested more than 100 pictorial stimuli, most of the neurons examined did not encounter the “optimal” pictures to which they would strongly respond. I finally overcame this difficulty by reducing the sample size of stimuli, and I successfully reproduced the finding within a practical testing time during which a single neuron could be kept stably at the electrode tip.

In July 1987, only two years after returning from Oxford and starting my own experiments, I wrote a paper on this finding and submitted it to the journal Nature. This paper, entitled “Neuronal Correlate of Pictorial Short-Term Memory in the Primate Temporal Cortex” (Miyashita and Chang, 1988), was accepted in November 1987 and published in January 1988.

Discovery of Visual Long-Term Memory Neurons

From the time that I discovered short-term memory neurons, I wondered whether a neuron responds to a particular picture by coincidence or as a result of learning. Through experiments conducted under various conditions to reproduce the finding in short-term memory neurons, I became convinced that the response was a result of learning. I formulated a hypothesis that these neurons constitute a neural basis that is responsible not only for short-term memory but also for storage of long-term memory of visual objects (“long-term memory neuron hypothesis”). Immediately after I posted the paper on short-term memory neurons to Nature, I fully engaged in a study to test this hypothesis. I had to conduct this study myself because Han Soo Chang had already left the Department of Physiology and returned to the Department of Neurosurgery. Whereas I had discovered short-term memory neurons serendipitously, to test the long-term memory neuron hypothesis, I had to proceed logically. I constructed the logic of the associativity of long-term memory and collected physiological evidence to demonstrate that logic. I already knew what kinds of neurons needed to be recorded and where in the temporal cortex I could find such neurons. I collected data quickly, all of which beautifully supported my hypothesis, and I submitted a paper on this theory along with the supporting evidence to Nature in July 1988. This paper, entitled “Neuronal Correlate of Visual Associative Long-Term Memory in the Primate Temporal Cortex,” was accepted in September and published in October 1988 (Miyashita, 1988). I am proud of this single-author paper, which was the first to report neurons that encoded long-term memory engrams in the cortical association areas.

This paper convincingly demonstrated the existence of long-term memory neurons with high probative value. However, I wanted to further broaden our understanding of this finding in two directions. First, I wanted to extend the finding by discovering the neuronal correlates of memory retrieval, as the October 1988 paper dealt with neuronal representation of long-term memory engrams (i.e., the mechanism of memory storage). Second, because the logic in the October 1988 paper was based on artificial experimental conditions (i.e., associativity was defined based on the order of displayed pictures), I wanted to confirm the finding under experimental conditions that were commonly used in psychology. These two aims could be achieved by introducing a behavioral task called a pair-association memory task into the electrophysiological study of monkeys. Pair-association memory tasks are standard memory tasks that were formulated in human neuropsychology and are included in psychological test batteries, such as the Wechsler Memory Scale–Revised (WMS-R), which are widely used around the world. In the WMS-R, the task is included under the category of the verbal and visual paired-associate learning test. Typically, people are asked to learn unrelated word pairs (e.g., elephant–rose) (verbal paired-associate learning test) or picture pairs (visual paired-associate learning test). At a later time, memory of those pairs is tested by having subjects recall one of the words/pictures in response to the word/picture it was paired with during encoding (e.g., recall the word that was paired with “elephant”). In our task, monkeys learned a large number of picture pairs and were trained to recall the paired associate of the presented cue stimulus.

It took two years to complete this study, and our findings were published in Nature in 1991 (Sakai and Miyashita, 1991). In this paper, we reported that monkeys could learn the pair-association memory task using visual stimuli, and that pair-coding neurons responsible for memory storage and pair-recall neurons responsible for memory retrieval could be identified within the framework of the task. Kuniyoshi Sakai, who was the first doctoral student in my laboratory, contributed prominently to this study.

The observations of this study were confirmed and developed in subsequent studies. Dr. Albright’s group demonstrated how the pair-coding property of the neurons develops in the course of the paired-associate learning in monkeys (Messinger et al., 2001; Albright, 2012). Another group also demonstrated a development of single-unit activity through visual stimulus association learning in monkeys (Erickson and Desimone, 1999). We demonstrated forward processing of encoding of stimulus-stimulus association memory in monkey inferotemporal cortex, and clarified the difference of memory encoding between the perirhinal cortex and area TE (Naya et al., 2003). Regarding the retrieval signal, we further clarified that the pair-recall neurons are activated with precise timing when the necessity for memory retrieval and its initiation time were signaled by an independent color switch rather than by the cue stimulus itself, suggesting the involvement of the pair-recall neurons in neural circuits underlying the on-demand reactivation of the representation under cognitive control (Naya et al., 1996). Therefore, the discovery of the pair-recall neurons has been frequently cited as some of the best neurobiological evidence supporting the “reactivation” theory of remembering (Buckner and Wheeler, 2001; Badre and Wagner, 2007; Danker and Anderson, 2010). The reactivation theory posits that domain-specific cortical regions and neurons are reactivated during vivid remembering and contribute to the contents of a memory. This theory has a long history, but it became popular after many functional magnetic resonance imaging (fMRI) studies found that certain brain regions that process incoming (bottom-up) perceptual information are also involved in representing that information during remembering (e.g., O’Craven and Kanwisher, 2000; Ishai et al., 2000). Finally, our 1991 study enabled us to identify the roles played by the memory neuron groups we discovered in various neuropsychological and clinical contexts, including human memory disorders. In 1993, for example, a study by Drs. Murray, Gaffan, and Mishkin (1993) reported that learning of a visual pair-association memory task by monkeys was impaired by a lesion in the temporal cortex (Murray et al., 1993), thus demonstrating the causal roles of the memory neuron group that we discovered. I synthesized these new discoveries into a neurophysiological theory of memory (Miyashita, 1993, 2004).

The discovery of the neural correlate of cortical long-term representations in explicit memory also opened up a door for neurobiologically reexamining some long-standing debates that had been mostly addressed only by behavioral or psychological approaches. One example is the issue of storage versus retrieval and the nature of memory impairment (for a review, see Squire, 2006). When memory impairment occurs, particularly after brain damage, including electroconvulsive therapy, head injury, and drug-induced amnesia, a question arises whether the impairment reflects impaired information storage (“storage deficit” view) or impaired accessibility (“retrieval deficit” view). Beginning in the 1970s, a considerable amount of work targeted the issue, but all the evidence was indirect based on behavioral analysis. We tackled the question directly with my monkey model of paired-associate learning (Higuchi and Miyashita, 1996) by applying the split-brain technique (one half of the hemispheres supported behavior, and the other half allowed for an evaluation of the lesion effects on pair-coding neurons). The study demonstrated that an ibotenic acid lesion of the rhinal cortex (perirhinal and entorhinal cortex) impaired the formation and maintenance of the associative representations between pairs of visual stimuli in area TE (adjacent lower-order neocortex). Thus, the findings demonstrated a strong case for the “storage deficit” view, providing some of the best evidence that memory loss involves an actual loss of the synaptic changes that support a memory.

Impact of the Discovery of Memory Neurons on the Neuroscience Community

After being recognized for my discovery of short-term and long-term memory neurons, I was assigned to take over Professor Masao Ito’s position at the university, and in 1989, I became the professor of the Department of Physiology in the University of Tokyo School of Medicine. I was more frequently invited to international symposia and had more opportunities than before for discussion with the world’s leading scientists. At the 13th European Conference on Visual Perception (ECVP90) held in Paris in September 1990, I met many rising stars with whom I have stayed friends for many years, including Drs. Bill Newsome, Patric Cavanaugh, and Shimon Ullman. I was particularly impressed by the achievements of Dr. Newsome, whose monumental work demonstrated a causal linkage between stimulus-selective neuronal firing and its behavioral impact in perception through microstimulation within area MT in monkeys. I remember a long discussion with Bill during the banquet at the senate held at ECVP90; our conversation was even more memorable than the taste of Sauternes and foie gras (although I no longer eat foie gras) at the banquet. In fact, at that time, Bill suggested that I should electrically stimulate my memory neurons and observe the behavioral impact of the stimulation, just as he did with direction-selective neurons in area MT. I never forgot his suggestion. But it took more than 20 years for me to complete the experiment and publish the results (Tamura et al., 2017): optogenetic stimulation of the memory neurons indeed provided strong behavioral impact as demonstrated by the stimulation-dependent shift of psychometric function for recognition. Both conceptual and technological refinements, including optogenetics in monkeys, were necessary during the 20-year interval.

The Fourth Conference on the Neurobiology of Learning and Memory, held at the University of California at Irvine the following month, in October 1990, also made a deep impression on me. I was so glad to meet Professor Jim McGaugh for the first time at this meeting. More importantly, I was overwhelmed by Professor Larry Squire, who served as a leader of the introduction and discussion sessions in the meeting, because of his long-range perspective and outlook based on clear rationales and broad knowledge. Since then, I have learned a lot from him at every turning point in my research.

To enable Japanese neuroscience to contribute to an international research alliance, we held a symposium entitled “Computation, Cognition, & Consciousness” at the International Institute for Advanced Studies in Kyoto from August 31 to September 3, 1994. The lectures from both experimental and theoretical neuroscientists, including Drs. Marcus E. Raichle, Michael Petrides, Edmund T. Rolls, Christoph von der Malsberg, and Jack D. Cowan, were amazing. In addition, I also invited philosophers specializing in mind-body problems, including Drs. Daniel C. Dennett, Owen Flanagan, and Junichi Murata, who were keen to engage in interdisciplinary exchanges with empirical scientists, particularly neuroscientists. In so doing, I was trying to realize my youthful dream of stimulating exchanges between philosophers and neuroscientists. In particular, a lecture by Dr. Daniel C. Dennett, entitled “Consciousness in Human and Robot Minds,” led to a heated discussion among participants. Furthermore, Dr. Michael Gazzaniga’s lecture, “Consciousness Is an Instinct,” deepened the discussion and impressed both neuroscientists and philosophers. The texts of these lectures were published in Cognition, Computation, & Consciousnes in 1997 by Oxford University Press.

Discovery of the Top-Down Signal from the Prefrontal Cortex

The discovery of memory neurons gave me an important basis for my life’s work. This prompted me to proceed further toward my distant dream of understanding how activity of the mind, as a psychological reality, emerges from the activity of the entire brain. Technically, as will be mentioned later, one of my new research directions was to measure whole-brain activity using neuroimaging, in particular, fMRI. Another new direction was to delve into such whole-brain activity toward the level of cellular network dynamics. To do that, I then took aim at the causal cognitive role of interaction between two brain regions and its physiological mechanisms in memory retrieval.

The theoretical basis of memory retrieval has long been discussed in a broader context of cognitive control (Tulving, 1985; Norman and Shallice, 1986), positing that the central function of memory retrieval is to bring knowledge to mind that is relevant to current goals and actions. Sometimes knowledge relevant to our goals comes to mind automatically, in a bottom-up fashion, simply by processing cues in our environment (“automatic retrieval”), typically when stimulus-stimulus or stimulus-response associations are strong. Often, however, relevant experiences from the past or facts about the world do not readily come to mind. In these instances, we must strategically search memory or trigger a strategic retrieval attempt and monitor its outcome (“controlled retrieval”; for more recent views on automatic and controlled retrieval, see Buckner and Wheeler, 2001; Badre and Wagner, 2007). The prefrontal cortex was considered to play a central role in controlled retrieval because patients with frontal cortical lesions often show retrieval difficulties, in particular when the specific context (or source) of an episode must be remembered or when minimal cues are provided to aid retrieval (Stuss and Benson, 1984; Schacter, 1987; Shimamura, 1995). On these grounds, I hypothesized that in controlled retrieval, a search signal for memory retrieval originates in a frontal lobe process and is sent to the memory neurons in the temporal lobe. I called this hypothetical signal “top-down signal for memory retrieval.” I also formulated a “strong version” of the top-down signal hypothesis whereby both bottom-up signals from the retina and top-down signals from the frontal lobe converge at temporal cortical memory neurons. If it is verified, the “strong version” of the top-down signal hypothesis would provide a neurobiological basis for the classic cognitive control theory of automatic and controlled retrieval (Norman and Shallice, 1986) as well as the “reactivation theory of remembering” that was described in the previous section, “Discovery of Visual Long-Term Memory Neurons.”

Until our discovery of pair-recall memory neurons in the temporal cortex in 1991, there had been no clue or experimental starting point to investigate the neurobiological basis of controlled retrieval, more specifically, no starting point to seek a top-down signal for memory retrieval as a physiological reality. The discovery of pair-recall neurons provided a starting point. I made a plan to demonstrate the existence of a top-down signal for memory retrieval and to analyze its specific characteristics using a physiological approach. To do that, I needed to conduct experiments in monkeys, but I wondered how to make monkeys perform controlled retrieval. I realized that I had to start by developing an experimental paradigm for monkeys.

Since my time in the Ito laboratory, I had been interested in the human split-brain studies conducted by Drs. Sperry and Gazzaniga (Gazzaniga, 1966, 1995) and I had used a split-brain monkey model in my study of the ”storage vs retrieval deficit” debate of memory impairment (Higuchi and Miyashita, 1996). One day, when I was trying to develop an experimental paradigm of controlled retrieval for monkeys, I came across a case report written by Dr. Gazzaniga’s group on memory retrieval in a patient with a partially split brain (Sidtis et al., 1981). This report detailed the process of controlled retrieval in this patient who had undergone partial posterior callosal commissurotomy (i.e., a posterior split-brain patient), based on the patient’s verbal report. For example, when the word “Knight” was presented to the left visual hemifield (i.e., to the right primary visual area) of patient J.W., he answered, “I have a picture in mind but can’t say it . . . Two fighters in a ring . . . Ancient wearing uniforms and helmets . . . on horses trying to knock each other off . . . Knights?”

Having got a clue from this article, I developed a partial split-brain (posterior split-brain) model that enabled me to make monkeys perform controlled retrieval. Because monkeys could not work in a verbal recall task, I designed a modification of the visual pair-association memory task. In this task, monkeys learned many pairs of different pictures, and a trial started when a randomly selected picture (cue picture) from a pair was presented to the right or left visual hemifield of the monkey. Then, choice pictures, including the paired associate of the cue picture, were presented to the right or left visual hemifield or both hemifields, depending on the recall conditions (“intra-hemispheric” recall or “inter-hemispheric” recall). Our behavioral experiment tested the inter-hemispheric transfer of memory engram of the paired associates and also tested the ability of inter-hemispheric cued-retrieval in the posterior split-brain monkeys. The experiment provided statistically robust evidence that memory control signals are produced in the frontal lobe of the cerebrum (i.e., brain regions dependent on the circuit that sends interhemispheric commissural fibers through the anterior part of the corpus callosum, including the genu), whereas long-term memory engrams of visual objects are located in the temporal lobe. We published the results in Science (Hasegawa et al., 1998). Please note that case studies in humans provide us with very interesting anecdotal findings, but it is difficult to statistically test the results. This behavioral evidence from monkeys also clarified the involvement of long-term memory engrams that reside in the memory neurons in the temporal lobe, and their functional roles in whole-brain neuronal circuits for controlled retrieval.

I was then ready to conduct an experiment to detect a top-down signal at a microelectrode tip during controlled retrieval. I designed this experiment to test the “strong version” of the top-down signal hypothesis whereby both bottom-up signals from the retina and top-down signals from the frontal lobe converge at temporal cortical memory neurons. Several aspects of this experiment required a high level of technical skill. For the experiment, the partial split-brain (posterior split-brain) monkeys learned and performed the modified visual pair-association memory task that was described in the previous paragraph. The monkeys were required to maintain fixation while they performed the pair-association memory task under both “intra-hemispheric” recall and “inter-hemispheric” recall conditions. A microelectrode recorded single-neuron activity in the temporal cortex over the course of several hours. If my “top-down signal for memory retrieval” hypothesis was correct, the top-down signal from the prefrontal cortex should be recorded in the “inter-hemispheric” recall condition. Here the cue stimulus is presented to the hemifield ipsilateral to the recording site. In this condition, the cue signal should travel a long way to reach a neuron recorded in the temporal cortex. The signal would first be sent to the contralateral primary visual area, then up to the contralateral frontal cortex, and, after being processed and traversing the anterior corpus callosum, eventually would reach temporal cortex as a top-down signal. The bottom-up signal should be recorded in the “intra-hemispheric” recall condition. In this condition, the cue stimulus is presented to the hemifield contralateral to the recording site and thus sent directly to the ipsilateral primary visual area and to neurons in temporal cortex. This task was difficult to conduct without highly motivated and cooperative monkeys. Hyoe Tomita, a graduate student in my laboratory, completed this difficult experiment and provided strong evidence for the hypothesized top-down signal for memory retrieval. We published the results in Nature (Tomita et al., 1999).

This experiment was the first to detect the top-down signal at the microelectrode tip and enabled analysis of the specific characteristics of the top-down signal. For example, we found that top-down signals conveyed categorical information about each picture, whereas bottom-up signals conveyed information specific to individual pictures. Through this study, we opened up a new way to characterize top-down signals using a rigorous electrophysiological method. Furthermore, the study also found that both the top-down and bottom-up signals converge onto a single temporal cortical neuron, which directly supported the “strong version” of the top-down memory retrieval hypothesis. Thus, it lent novel neurobiological support to classic ideas, such as controlled retrieval theory and reactivation theory of remembering as discussed previously (Miyashita and Hayashi, 2000). The figures included in this paper were cited in Principles of Neural Science, fifth edition (Kandel et al., McGraw-Hill Medical, 2013), and the paper has been recognized as a groundbreaking article that substantiated the concept of top-down signals.

Toward a Comprehensive Understanding of the Cortical Memory System: Local Circuits and Global Networks

The discovery of top-down signals in controlled retrieval ignited an ambition to conduct a comprehensive analysis of brain-wide cortical mechanisms related to declarative memory (explicit memory), with the goal of elucidating the whole picture of the activities of both local circuits and global networks within the monkey cortex. I endeavored to fulfill that ambition for over 15 years. During that time, my achievements included the discovery of recall signals for automatic memory retrieval, which are transmitted between areas in the temporal cortex in a retrograde manner (Naya et al., 2001); elucidation of the roles of the premotor area of the frontal lobe in output control in a sequence of memorized items (Ohbayashi et al., 2003); elucidation of the roles of temporal cortical memory neurons in working memory, particularly in the presence of distracters (Takeda et al., 2005); optogenetic proof that readout from memory neurons in the temporal cortex causally affects memory-based judgments (Tamura et al., 2017); and analyses of local circuit dynamics that enable encoding and retrieval in the memory neurons in the temporal cortex (Takeuchi et al., 2011; Hirabayashi et al., 2013a, 2013b; Takeda et al., 2015; Koyano et al., 2016). The initial concept of this long-term project was explicitly described in a review article published in Science in 2004 (Miyashita, 2004), and the findings were summarized in a review article published in the Nature Review of Neuroscience in 2019 (Miyashita, 2019).

In the course of these studies, we had to develop several new technologies ourselves. For example, to investigate local neuronal circuit dynamics within the cortical association areas (e.g., the perirhinal cortex or area TE), it was necessary to determine in which of the six layers of the cerebral cortex the neurons of interest were located, while recording single-neuron activity in monkeys during a cognitive task. At that time, however, there was no technology to make this possible. Therefore, Teppei Matsui and Kenji Koyano, who were graduate students in my laboratory, and I developed a new method to accomplish this using high-field MRI. The tip of a microelectrode inserted into the monkey cortex is typically invisible in conventional MRI because of a partial volume effect, but we demonstrated that the position of the electrode tip can be detected in high-resolution structural MR images with enhanced detectability. With this technique, the electrode image is made very thick by the enhancement caused by the interaction between the static magnetic field and the electrode metal, while the spatial resolution along the electrode is preserved. Using this method with fast spin echo 4.7T MR imaging, Matsui et al. (2007) were able to identify microelectrode tip locations with single-voxel accuracy (less than 100 µm) (Matsui et al., 2007). At present, 7 T MRI enables determination of tip locations at a voxel size of 50 µm or less.

In addition, we developed another, perhaps more easily accessible, method than the MRI method, which uses current-source-density (CSD) analysis and a linear-array multichannel electrode. The CSD is a reflection of the net transmembrane currents in a local neuronal ensemble and is calculated from stimulus-evoked local field potentials recorded at different depths within the cortical tissue (Nicholson and Freeman, 1975). We found that, within the temporal association cortex, the earliest current sink induced by an optimal visual stimulus provides a good estimate of the position of the granular layer (layer 4) (Takeuchi et al., 2011). Therefore, this method enabled us to assign a large number of simultaneously recorded neurons into a supragranular layer (layers 2/3), granular layer (layer 4), and infragranular layer (layers 5/6). We then analyzed the time series of simultaneously recorded neuronal spikes using spike-spike time series correlation and the Granger-causality method, which enabled us to determine the flow of signals between neurons (Hirabayashi et al., 2010, 2013a, 2013b; Takeuchi et al., 2011; Hirabayashi and Miyashita, 2014; Takeda et al., 2015).

The development of these new technologies enabled us to elucidate the dynamics of the neuronal circuits underlying memory retrieval. Here, I briefly summarize the findings of my studies on the cortical semantic memory system for visual objects. [Note: it would be more accurate to call it “semantic-like memory” because the study was conducted in monkeys. For the conceptualization of “semantic-like memory,” please refer to Miyashita, Nature Review of Neuroscience (2019)].

It is now generally agreed that semantic memories of visual objects are stored and represented in a distributed network encompassing multiple cortical areas. These cortical areas are hierarchically organized such that the perirhinal cortex (PRC) (Brodmann area 35/36) is at the apex of the brain-wide network. Various attributes of visual objects are represented in the downstream areas of the PRC. For example, a major downstream area adjacent to the PRC, area TE, is a unimodal visual association area in monkeys, where information about the shapes of visual objects is represented (Gross, 1992; Miyashita, 1993; Tanaka, 1996). In terms of memory storage, the PRC integrates various attributes represented in area TE and other areas into the images of an individual object through an association mechanism (Yoshida et al., 2003; Hirabayashi et al., 2013b; Hirabayashi and Miyashita, 2014). In terms of memory retrieval, when we see an object, the representation of the object’s identity that is activated in the PRC triggers backward sequential activation from the PRC and retrieval of object-associated features, which are represented in the PRC and other downstream cortical areas, eventually activating all attributes of the object, one after another (Naya et al., 2001; Takeda et al., 2015). The origin of the backward retrieval signal is in the PRC, and the first backward retrieval signal is generated in layer 5 of the PRC (Koyano et al., 2016) by a direction-specific interaction between a neuron encoding an object that is a cue to memory recall and a neuron encoding a to-be-recalled object (Hirabayashi et al., 2013a; Hirabayashi and Miyashita, 2014). The backward retrieval signal is transmitted from the infragranular layer in the higher-order cortical areas to the infragranular layer in the lower-order cortical areas (Takeda et al., 2015). The basic machinery that enables the retrieval of semantic-like memory is serial activation via backward projections from the PRC, which drive retrieval of nested associations. Moreover, in each area, the activity is transmitted from the infragranular layer to the supragranular layer (Takeuchi et al., 2011). It then reads out the attribute information that is represented in each area. The circuit dynamics that send signals from the infragranular layer to the supragranular layer was also a new discovery, shedding new light on the functional principles of local neuronal circuit dynamics within the cerebral cortex (Takeuchi et al., 2011; Miyashita, 2019). These ideas differed from the standard mode of signal transduction found in the primary sensory areas (conventionally known as a “canonical circuit”) that sends signals from the supragranular layer to the infragranular layer (Douglas and Martin, 2004; Harris and Shepherd, 2015).

We also investigated molecular mechanisms of memory circuit formation in the primate. Because the number of monkeys available for such molecular studies was limited, a new research strategy for monkeys was required that was different from the methods used with rodents. Hiroyuki Okuno and Wataru Tokuyama, graduate students in my lab, developed a new efficient assay strategy using a split-brain monkey (Okuno et al., 1999; Tokuyama et al., 2000). To eliminate genetic and cognitive variations between individual animals, we used split-brain monkeys for intra-animal comparisons in PCR-based mRNA quantitation. The monkeys learned a pair-association task using one hemisphere and a control visual task using the other, to balance the amount of visual input to each hemisphere. We found that several molecules, particularly BDNF, was upregulated selectively in the PRC during pair-association learning, but not in areas involved in earlier stages of visual processing (Tokuyama et al., 2000; Tokuyama et al., 2002). The results not only revealed molecular substrates for memory circuit formation in the primate temporal cortex but also confirmed the unique position of the PRC in memory formation in the primate. Some of my students were also interested in synaptic/spine mechanisms that support memory formation (Matsuzaki et al., 2001)

These discoveries were reported in various invited lectures (presidential special lectures/plenary lectures) at international meetings, such as those of the Society for Neuroscience, the International Brain Research Organization, and the Federation of European Neuroscience Societies. I was particularly glad to be invited to the McGill University Brenda Milner Memorial Symposium, held in Montreal, Canada, in September 2003 to celebrate the 85th birthday of Professor Brenda Milner, whom I have highly respected for a long time. This symposium also enabled me to renew old friendships with such pioneers as Drs. John O’Keefe, Larry Squire, Trever Robbins, and Michel Petrides, all of whom I have greatly respected. It was an unforgettable symposium for me. Although I could not attend Professor Brenda Milner’s 100th birthday celebration event held on July 15, 2018, because of my recent appointment as director of the RIKEN Center for Brain Science, I was glad that I could listen to her voice in a video clip uploaded to YouTube.

Beyond Memory Research: At the Rise of Functional Magnetic Resonance Imaging

In parallel with the Local Circuits and Global Networks project described in the previous section, in the early 1990s, I started to think about broadening the scope of my own research beyond the narrowly defined memory processes, “encoding, storage and retrieval,” which have long been investigated in neuroscience. Conceptually, I wanted to look for a new research target in the field of high-level cognition, which, up to that time, had been mostly behaviorally investigated in humans. Methodologically, I wanted to introduce a new imaging technology, functional magnetic resonance imaging (fMRI), into my laboratory. This would enable me to visualize neural activity throughout the entire brain in humans.

My research interest in fMRI began just at the time of Dr. Seiji Ogawa’s seminal publications reporting the discovery of blood-oxygenation-level-dependent (BOLD) imaging (Ogawa et al., 1990; Ogawa et al., 1992). At that time, however, no MR scanner was available for basic scientific research at the University of Tokyo. Although there were several clinical MR scanners at the University of Tokyo Hospital, these instruments were not able to perform echo-planar imaging (EPI), which is an essential MR pulse sequence that enables scanning at high temporal resolution. In 1992, therefore, together with Kuniyoshi Sakai, a research associate in my lab, I began work outside the University of Tokyo on a feasibility study assessing the BOLD effect. This entailed frequently traveling 30 km back and forth to the Hitachi Central Research Laboratory (HCRL) in Kokubunji-shi, where they had an MR scanner supporting EPI sequence. In 1995, our team published two papers detailing the findings of the feasibility on the BOLD effects using the HCRL scanner (Sakai et al., 1995a, 1995b). This initial success enabled us to persuade the University of Tokyo to purchase a new 1.5 T MR scanner that was EPI-compatible and dedicated to basic research. The results of the feasibility study also convinced me of the tremendous potential of fMRI as a new, whole-brain imaging methodology to analyze higher cognitive function in both human and non-human primates.

The mid-1990s were a time of rapid growth of fMRI-related research worldwide, and my lab was no different. With a group led by Seiki Konishi, a graduate student in my lab at the time, we sought new technical and conceptual approaches to the use of fMRI. One such approach was the “event-related design” for fMRI studies, an imaging methodology we proposed in 1996 as an alternative to the then-standard “block design” (Konishi et al., 1996). Unfortunately, we were unaware that the same idea was being thoroughly developed by a group at University College London led by Drs. Richard Frackowiak and Karl Friston. Richard later became a trusted advisor to our lab on imaging studies. We wanted to demonstrate that the new event-related fMRI method could be used to rigorously analyze complex cognitive processes, something that had been difficult using conventional “block design” imaging approaches. After a series of pilot studies confirmed our approach’s feasibility (Konishi et al., 1998a), we prepared to plunge headfirst into the competitive neuroimaging community with a new project targeting the functional analysis of the human frontal lobe. Our first foray (Konishi et al., 1998b) was the application of event-related fMRI to the Wisconsin Card Sorting Test (WCST), a standard neuropsychological test used to detect frontal lobe dysfunction. This was the first attempt to deconstruct the complex prefrontal neural processes enabling cognitive set-shifting into subprocesses that could be localized in different prefrontal areas. The WCST treats a subject’s performance as reflective of a single mental process in neuropsychological terms; however, our research in subsequent years showed that the cognitive set-shifting in question actually emerges from the interplay of “bundles” of multiple processes within the frontal cortex (Konishi et al., 1999a, 1999b, 2002, 2003, 2005, 2006, 2008). We also demonstrated that the same basic principle applies to other domains of cognition such as “response inhibition” that can be tested with go/no-go decision tasks (i.e., the go/no-go decision actually emerges from the interplay of “bundles” of multiple processes within the cortex) (Konishi et al., 1998a; Chikazoe et al., 2007, 2009a, 2009b). Some graduate students in my lab were also interested in single-cell studies of the WCST and in testing causality with focal neuronal suppression in monkeys (Kamigaki et al., 2009, 2012).

I remained interested in all mental processes ongoing within the frontal lobe, but I simultaneously attempted to test the possibility of using fMRI to investigate cognitive functions unique to humans. At that time, as now, the cognitive functions that were “unique to humans” brought to my mind those involved in language, especially syntax. In 1996, one year after installation of the MRI scanner in my laboratory, I launched a joint project in partnership with another group led by Professor Wayne O’Neil in the Department of Linguistics and Philosophy at the Massachusetts Institute of Technology (MIT). Domestic research funding was provided by the Japan Science and Technology Agency. This joint project yielded interesting results, demonstrating the neural basis of syntactic specialization in Broca’s area (Embick et al., 2000). In addition, there were enjoyable discussions with two young, highly focused linguistics researchers at MIT, who are now working at New York University (NYU): Drs. Alec Marantz (Department of Linguistics, NYU) and David Poeppel (Department of Psychology, NYU). One of my fondest memories from the time was the “Image, Language, Brain” symposium that I held in Tokyo in November 1998, early on in our collaboration. Professor Noam Chomsky’s lecture “Linguistics and Brain Science” left a deep impression on the hundreds of people in attendance. Speakers from other disciplines included Drs. Richard Frackowiak and Robert Desimone in brain science and Drs. Helen Neville, Jacques Mehler, Angela Friederici, and Willem Levelt in linguistics. An exuberant optimism was sensed on both the linguistics and neuroscience sides. All were passionate about designing new neuroscientific approaches for human language. The symposium highlights were later compiled and published as Image, Language, Brain in 2000 by MIT Press.

Whole Brain Metamemory Network: Monkey fMRI and Causal Evidence

I learned a lot from the joint project with MIT linguistics, and we published a lot after developing new technical tools for neuroscientific research into linguistics, including source-localization algorithms in magnetoencephalography (MEG) (Sekihara et al., 1997, 1998a, 1998b, 1999a, 1999b, 2000, 2001, 2002). Dr. Kuniyoshi Sakai, a main booster of the joint project from the Japanese side, decided to devote his scientific career to fMRI-MEG analysis of language syntax. Those were all fine. However, the causality issue bothered me. With the benefit of hindsight, I began to wonder if an fMRI-MEG approach to language syntax would face insurmountable methodological hurdles unless it was combined with human genetics. This is because research in humans cannot rely on finely targeted invasive approaches, such as lesioning or pharmacological suppression of neural activity (e.g., using muscimol) for investigation of the causal links between neural events and behavior. (Of course, I agree that neuropsychology is a powerful approach to investigating causality.) It was then that I heard about the discovery of the FOXP2 gene. However, I was unsure at that time whether analyses of human genetics would uncover additional syntax-related genes.

So, where to go? Since my student days, I had dreamed of reconceptualizing the philosophical thoughts of Maurice Merleau-Ponty and Edmund Husserl within the framework of natural science. Several trials and errors later, I decided on metacognition as a primary target of my subsequent research. In its long history since the time of Rene Descartes or William James, self-reflection has been recognized to be a distinguishing mental process of the human mind. Recently, it has been extensively explored in human psychology through analytical characterization of various types of metacognitive processes (Leonesio and Nelson, 1990; Nelson, 1996; Schacter, 1998). Moreover, I recognized a latent opportunity to design a realistic animal model of metacognition, the possibility of which has been discussed among behavioral scientists since the late 1990s (Shields et al., 1997; Hampton, 2001; Hampton et al., 2004; Smith, 2009).

I decided to start with human fMRI studies. There was already an abundance of psychological literature touching on metacognition via behavioral approaches. I therefore searched for a behavioral task that could withstand the strict scrutiny of neuroscientific analysis. First and foremost, the task would need to be compatible with event-related fMRI. Together with Hideyuki Kikyo, a graduate student in my lab, I successfully formalized the so-called FOK (“Feeling-Of-Knowing”) task for human subjects, and published our first fMRI paper on FOK in 2002 (Kikyo et al., 2002). FOK is a form of metamemory that refers to the ability to predict the successful retrieval of information about a particular subject (Hart, 1967; Nelson, 1984; Metcalfe et al., 1993). FOK judgments do not focus on the ability to answer the question correctly, but rather on the ability to predict whether, even when one cannot recall an answer to the question, one would be able to recall the correct answer if given a hint or more time (high FOK rating if YES, and low FOK rating if NO). Using a parametric design of fMRI experiments, we identified several FOK-related areas, all of which were located in the prefrontal cortex. Interestingly, activation patterns in these regions did not necessarily depend on the difficulty of memory retrieval, recall effort, or response time. Moreover, the activation patterns in some regions correlated with whether the retrieval succeeded or failed, as typically has been seen in the parietal cortex, but activation patterns in other regions did not. All the lines of evidence suggested that these neural correlates of FOK in the prefrontal cortex play differential roles in generating FOK. [Note: We were not aware that a research group at the Department of Psychology, Harvard University, was motivated by a similar perspective (Maril et al., 2003). This fMRI research topic was far from popular at that time, and when I learned of their work I realized how much international competition and cooperation was being fostered by the evolution of fMRI research.]

I believed that clarification of the “division of roles” among the identified FOK-related areas was of great importance. I therefore sought to delve deeper into the functional architecture of the metacognition network. Notably, analysis of the causal impact exerted by each candidate area upon metacognitive behavior would be crucial to this research. This causal analysis should be done on the basis of correlational analyses (e.g., fMRI studies). Our correlational analysis of the “division of roles” went relatively straightforwardly in human subjects, but causal analysis would have been difficult using human subjects.

One potential solution was transcranial magnetic stimulation (TMS), a powerful technique capable of halting neural activity in specific targeted regions of the brain, which has been applied in human research. After serious consideration, however, I decided against its use in 2002 because of the ethical constraints on TMS usage in Japan at the time, and because of the relatively low spatial resolution for determining the border of the TMS-inactivated area. Abandoning TMS was a difficult decision, as it meant, in effect, that we would not be studying this problem in humans. To probe the biological mechanisms underpinning metamemory using a more invasive approach demanded that we develop an experimental animal model for the process, along with an fMRI methodology equally suited to human and animal research. I decided that macaque monkeys would be the optimum model animal for both purposes. And since 2002 or a bit earlier on, my laboratory has been tackling these two challenges in parallel with our continuing analysis of the global networks and local circuits involved in memory (i.e., encoding, maintenance, and retrieval), as described in earlier sections.

fMRI studies in monkeys required a more powerful scanner than the standard 1.5 T unit we had been using to date. I elected for a 4.7 T BioSpec system produced by Bruker BioSpin. The scanner had a high static field strength magnet and a high slew rate gradient field coil, enabling it to take remarkably high-resolution images as compared with the standard clinical MR models. Furthermore, I valued the high degree of freedom it provided users to design customized pulse sequences and other parameters, empowering them to find their own solutions to any artifacts—the bane of high-field MR imaging. We developed our monkey fMRI paradigm from a variety of perspectives while comparing the performance of the 1.5 T and 4.7 T scanners. This ranged from complex cognitive task paradigms, such as the WCST, to simpler eye movement paradigms, such as saccades (Nakahara et al., 2002; Koyama et al., 2004; Adachi et al., 2012; Miyamoto et al., 2013, 2014; Osada et al., 2015). Through this work, we joined an international alliance of researchers who considered MR imaging approaches in monkeys quite useful and worked hard to develop new MR technologies adapted for monkeys. In the 1990s to 2000s this included Drs. Nikos Logothesis (Max Planck Institute), Guy Orban (Katholieke Universiteit Leuven), and Wim Vandeffel (Harvard University). Not only did I enjoy and value their friendship, these colleagues have helped me to advance and evolve my research, technically and conceptually.

The development of an experimental animal paradigm for metamemory was by no means easy. I first declared this research goal to the world in November 2005, in the Presidential Special Lecture at the 35th Society for Neuroscience Meeting held in Washington, DC. Initially, we pursued the idea of training macaques on our original FOK task that was applied to human subjects in our previous projects (Kikyo et al., 2002). However, training a monkey, even outside a MR scanner, was difficult, and measurement inside the MR scanner was never successful. I gave up on this approach and decided to design a new task for monkeys. Finally, after spending nearly a decade on wrong turns and redesigning, we finalized our “metamemory confidence task for monkeys,” which is a two-stage metacognition task with a postdecision wagering paradigm for macaques. In a trial of this task, the monkeys first performed a recognition memory test. They then made a wager on the expectation of their performance (or confidence) in the preceding memory decision by choosing either a high-bet or low-bet option. If they chose the high-bet option, they received a large reward after a correct memory decision, but they would have to wait a long time without receiving any reward after an incorrect memory decision. This high-bet option corresponds to the exploitation of reward while taking a risk when they believe the reward is a sure thing. By contrast, if the monkeys chose the low-bet option, they received a small reward with no risk of a long time-out penalty, irrespective of their memory decision. The contribution of Kentaro Miyamoto, a graduate student in my lab at the time, to this metamemory project was immense, even during the design phase of the task.

The postdecision wagering paradigm was difficult for monkeys to understand; it took several months to train them even outside of the MR scanner. It then took several more months for them to perform the task in the MR scanner, where they were subjected to the loud scanner noise. Just verifying that they were truly performing the task correctly, using meta-d-prime and other behavioral metrics, also took time. Nonetheless, thanks to Kentaro’s persistence and resolve, we successfully trained the monkeys to complete the task inside the MR scanner.

From whole-brain fMRI data obtained during performance of the task, we found that, during the memory test phase, before the bet, the dorsal prefrontal cortex (area 9; anterior area from the posterior supraprincipal dimple, aPSPD), the anterior supplementary eye field area (area 6; SEFa), and the frontopolar cortex (area 10; FPC) confer self-confidence on a remotely experienced event, a recently experienced event, and a nonexperienced event (Miyamoto et al., 2017, 2018). That is, activity in aPSPD was significantly positively correlated with a metacognitive behavioral index of self-confidence, Φ, for a remotely experienced event, but not on a recently experienced event, or a nonexperienced event. The phi coefficient (Φ) is a contingency table–based statistical index of preference for optimal choice (Middlebrooks & Sommer, 2011). Similarly, activity in SEFa was significantly positively correlated with self-confidence Φ only for a recently experienced event, and activity in FPC was significantly positively correlated with self-confidence Φ only for a nonexperienced event. We also discovered that focal inactivation of neuronal activity specific to the bilateral aPSPD, SEFa, or FPC using muscimol selectively impairs metacognitive judgments about remote memory, recent memory, or nonexperienced events, respectively, without impairing recognition performance itself (Miyamoto et al., 2017, 2018). I therefore suggest that our metacognition on retrospection is actually supported by bundles of readout streams for metamemory via different prefrontal areas rather than by a single unified site devoted to metacognition in general. If I generalize it a little loosely, the result has provided evidence that our consciousness is supported, not by a single unified cortical “consciousness” site, but by bundles of “consciousness” streams via different cortical areas.

The greatest strength of this three-pronged strategy, which combines an animal model of metamemory, whole-brain fMRI, and finely targeted local inactivation of cortical activity, is that it opens avenues through which to directly probe the causal brain mechanisms governing high-level cognition, such as metamemory. A good example is that this approach enabled us to discover a novel neural correlate of metamemory in a largely uninvestigated area of the dorsal prefrontal cortex, located at the aPSPD, around the boundary of anatomically defined area 9 and 9/46d in monkeys. Neuroimaging can identify specific activation patterns and regions that appear during the performance of a task, but this evidence merely indicates a temporal correlation between brain and mental activities. The level of evidence required to answer the question, “Does this signal or region actually generate the mental activity in a causal manner?” is not achievable with fMRI alone. Describing the behavioral consequences of suppressing the function of a region or network identified in fMRI would provide the most compelling evidence of a causal link. To more broadly examine the promise of such ideas, I held an international symposium entitled “Vision, Memory, Thought: How Cognition Emerges from Neural Network” in Tokyo in December 2014. The symposium also aimed to discuss how we can link recent network analyses at microscopic (single-axon wiring), mesoscopic (cortical interlaminar connections), and macroscopic (interareal functional connectivity) levels. Among the speakers who discussed the challenges of linking these different levels of networks were: Drs. Bill Newsome, Stanislas Dehaene, Doris Tsao, Karl Deisseroth, Takao Hensch, Nikos Logothetis, and Edward Moser.

Since our first fMRI report on the visualization of human metacognition in 2002, I have spent the past 20 years or so trying to pave the way for new methodologies to explore the whole-brain network underlying metacognition, substantiated by causal evidence. I have cleared the first step toward achieving the dream of my youth, substantiating the philosophy espoused in The Structure of Behavior and Phenomenology of Perception in the natural sciences. I am deeply grateful to all my collaborators who have traveled this road with me, especially to those I first met as graduate students in my laboratory, who are now working as principal investigators in their independent positions all over the world, including the United States, Europe, China, and Singapore.

Dedication to Community and RIKEN Center for Brain Science

My life as a researcher has spanned more than 40 years, and I am keenly aware of all the support and help I have received from both the Japanese and international scientific communities at every step along the way. One of my missions, I believed, was to devote myself to the development of the scientific community at both the national and international levels, for example, in my membership on the Board of Reviewing Editors of Science and my longstanding involvement in the Japan Neuroscience Society and the Society for Neuroscience. However, I continue to feel that these purely scholarly activities lack something: a deeper connection to the public. Society would reap the benefits of our research more broadly and deeply if our activities were synchronized and unified across the many relevant clinical organizations. In 2012, while President of the Japan Neuroscience Society, I founded the Union of Brain Science Associations in Japan (UBSAJ). This is a consortium of academic organizations engaged not only in particular kinds of neuroscience (e.g., neuroscience, neurochemistry, and neural networks, etc.) but also in clinical research (e.g., neurology, psychiatry, neurosurgery, rehabilitation, and magnetic resonance in medicine, etc.) and brain-related basic research (e.g., anatomy, physiology, pharmacology, psychology, and neuropsychology). The UBSAJ has grown in both strength and scope, making waves affecting not only academia but also social policy. It has influenced, for example, the Japanese government more than the Japan Neuroscience Society—or any single organization—could alone.

In April 2018, I succeeded Dr. Susumu Tonegawa as director of the RIKEN Center for Brain Science (CBS), Japan’s largest neuroscience institute. Dr. Masao Ito was the first director when the center was known as the RIKEN Brain Science Institute (BSI). The advanced level and thematic breadth of the research carried out at this institute, along with the diversity of its membership, have earned it an excellent reputation and global visibility. Unfortunately, RIKEN BSI’s budget has experienced heavy cuts in the years leading up to 2017, presenting BSI with the problem of stagnant PI recruitment. Since taking office, I have overseen dramatic reforms at the center, shoring up our funding sources and starting to recruit new faculty members from the international neuroscience community. This series of reforms, I hope, will revitalize and rejuvenate the RIKEN CBS, enabling us to freshly contribute to the Japanese and international scientific communities in the coming years.

Interim Review and the Next

My research began from two starting points. One was mathematics and physics, which I first encountered in George Gamow’s books, Mr. Tompkins in Wonderland and One Two Three . . . Infinity. I am indebted to George Gamow for fostering in me an interest in special relativity theory and infinite set theory, ultimately leading me to an appreciation of the mathematical beauty of the world. The other starting point was a reading club with my friends where we read the books of Merleau-Ponty and Husserl during junior high and high school. These books imprinted on me the mysteries of the human mind, particularly the enigma of self-reflection that interacts with the subconscious mind in unfathomable ways. Of course, the road to realization of the dream of my youth, to integrate these two starting points into one, was long and tough and still incomplete. Wissenschaft als Beruf (Science as a Vocation) by Max Weber taught me to cool my head by warning me not to be carried away by naïve ideas and literary rhetoric and not to ignore facts about the brain. I am heavily indebted to my academic role models, including Dr. Masao Ito, who developed the cerebellar learning theory and its experimental support; Dr. David Marr, who set out the idea of computational vision; and Dr. Susumu Tonegawa, who always demanded causal evidence. Although I was tested by these academic role models, the dream of my youth survived. And a part of that dream, which was nurtured by Phenomenology of Perception and The Logic of Scientific Discovery, is coming true in the world of neuroscience. This has been a long journey that has entailed the discovery of memory neurons and the top-down signal for memory retrieval from the prefrontal cortex, as well as the identification and elucidation of cortical global networks and local circuits for memory retrieval [reviewed in Miyashita (2019)]. This has further developed into the identification and causal analysis of the metamemory center within the prefrontal cortex. I have lived a happy life as a researcher. I would like to express my deep gratitude to my collaborators, including the graduate students in my laboratory, who worked with me on difficult projects. I would also thank my colleagues who not only deepened my research but also encouraged me through discussions at academic meetings and healthy critical reviews of my papers.

That being said, my investigations of brain metacognition circuits have just begun. The whole-brain network of metamemory will be scrutinized through various viewpoints with monkey fMRI, since a single cognitive-subtraction approach often misses an important activation due to the problem of statistical stringency. This sounds promising to me as I will be able to test the causal roles of candidate fMRI-activation areas by focal inactivation tests and by determining their impact on metacognitive behavior. Furthermore, I will be applying all the cutting-edge neurobiological methods that I have used in my studies of memory in monkeys in the past 30 years, from now on to analyze metacognition, that is, to analyze “local circuits and global networks of metacognition.” These neurobiological methods will include simultaneous recording of the activity of a large number of neurons with electrode arrays, spike-spike time series correlation analysis and their Granger-causality analysis to determine the flow of signals among neurons, structural MRI- or CSD-based anatomy-function analysis of cortical layers, and optogenetic interventions with excitatory and inhibitory opsins combined with effectively engineered promotors and tracer molecules. I am very excited about this work.

References

Adachi Y, Osada T, Sporns O, Watanabe T, Matsui T, Miyamoto K, Miyashita Y (2012) Functional connectivity between anatomically unconnected areas is shaped by collective network-level effects in the macaque cortex. Cereb Cortex. 22: 1586–92.

Albright TD (2012) On the perception of probable things: neural substrates of associative memory, imagery, and perception. Neuron. 74: 227–45.

Badre D, Wagner AD (2007) Left ventrolateral prefrontal cortex and the cognitive control of memory. Neuropsychologia. 45: 2883–901.

Buckner RL, Wheeler ME (2001) The cognitive neuroscience of remembering. Nat Rev Neurosci. 2: 624–34.

Chikazoe J, Konishi S, Asari T, Jimura K, Miyashita Y (2007) Activation of right inferior frontal gyrus during response inhibition across response modalities. J Cognit Neurosci. 19: 69–80.

Chikazoe J, Jimura K, Hirose S, Yamashita K, Miyashita Y, Konishi S (2009a) Preparation to inhibit a response complements response inhibition during performance of a stop-signal task. J Neurosci. 29: 15870–77.

Chikazoe J, Jimura K, Asari T, Yamashita K, Morimoto H, Hirose S, Miyashita Y, Konishi S (2009b) Functional dissociation in right inferior frontal cortex during performance of go/no-go task. Cereb Cortex. 19: 146–52.

Danker JF, Anderson JR (2010). The ghosts of brain states past: Remembering reactivates the brain regions engaged during encoding. Psychol Bull. 136: 87–102.

Douglas RJ, Martin KAC (2004) Neuronal circuits of the neocortex. Ann Rev Neurosci. 27: 419–51.

Dufosse M, Ito M, Jastreboff PJ, Miyashita Y (1978) A neuronal correlate in rabbit’s cerebellum to adaptive modification of the vestibulo-ocular reflex. Brain Res. 150: 611–16.

Eacott MJ, Gaffan D, Murray EA (1994) Preserved recognition memory for small sets, and impaired stimulus identification for large sets, following rhinal cortex ablations in monkeys. Eur J Neurosci. 6: 1466–78.

Embick D, Marantz A, Miyashita Y, O’Neil W, Sakai KL (2000) A syntactic specialization for Broca’s area. Proc Natl Acad Sci USA. 97: 6150–54.

Erickson CA, Desimone R (1999) Responses of macaque perirhinal neurons during and after visual stimulus association learning. J Neurosci. 19: 10404–16.

Felleman DJ, Van Essen DC (1991) Distributed hierarchical processing in the primate cerebral cortex. Cereb Cortex. 1: 1–47.

Gazzaniga MS (1966) Interhemispheric communication of visual learning. Neuropsychologia. 4: 183–89.

Gazzaniga MS (1995) Principles of human brain organization derived from split-brain studies. Neuron. 14: 217–28.

Gross CG (1992) Representation of visual stimuli in inferior temporal cortex. Phil Trans Royal Soc London B, Biol Sci. 335: 3–10.

Gross CG, Bender DB, Rocha-Miranda CE (1969) Visual receptive fields of neurons in inferotemporal cortex of the monkey. Science. 166: 1303–06.

Gross CG, Rocha-Miranda CE, Bender DB (1972) Visual properties of neurons in inferotemporal cortex of the Macaque. J Neurophysiol. 35: 96–111.

Hampton RR (2001) Rhesus monkeys know when they remember. Proc Natl Acad Sci USA. 98: 5359–62.

Hampton RR, Zivin A, Murray EA (2004) Rhesus monkeys (Macaca mulatta) discriminate between knowing and not knowing and collect information as needed before acting. Anim Cognit. 7: 239–46.

Harris KD, Shepherd GM (2015) The neocortical circuit: themes and variations. Nature Neruosci. 18: 170–81.

Hart JT (1967) Memory and memory-monitoring process. J Verbal Learn Verbal Behav. 6: 685–91.

Hasegawa I, Fukushima T, Ihara T, Miyashita Y (1998) Callosal window between prefrontal cortices: cognitive interaction to retrieve long-term memory. Science. 281: 814–18.

Higuchi S, Miyashita Y (1996) Formation of mnemonic neuronal responses to visual paired associates in inferotemporal cortex is impaired by perirhinal and entorhinal lesions. Proc Natl Acad Sci USA. 93: 739–43.

Hirabayashi T, Miyashita Y (2014) Computational principles of microcircuits for visual object processing in the macaque temporal cortex. Trends Neurosci. 37: 178–87.

Hirabayashi T, Takeuchi D, Tamura K, Miyashita Y (2010) Triphasic dynamics of stimulus-dependent information flow between single neurons in macaque inferior temporal cortex. J Neurosci. 30: 10407–21.

Hirabayashi T, Takeuchi D, Tamura K, Miyashita Y (2013a) Functional microcircuit recruited during retrieval of object association memory in monkey perirhinal cortex. Neuron. 77: 192–203.

Hirabayashi T, Takeuchi D, Tamura K, Miyashita Y (2013b) Microcircuits for hierarchical elaboration of object coding across primate temporal areas. Science. 341: 191–95.

Ishai A, Ungerleider LG, Haxby JV (2000) Distributed neural systems for the generation of visual images. Neuron. 28: 979–90.

Ito M (1970) Neurophysiological aspects of the cerebellar motor control system. Int J Neurol. 7: 162–76.

Ito M (1974) The control mechanisms of cerebellar motor system. In Schmitt FO, Worden FG, eds. The Neurosciences: Third Study Program. Cambridge, MA: MIT Press, 293–303.

Ito M (1984) The Cerebellum and Neural Control. New York: Raven Press.

Ito M (2006) Cerebellar circuitry as a neuronal machine. Prog Neurobiol. 78: 272–303.

Ito M, Miyashita Y (1975) The effects of chronic destruction of the inferior olive upon visual modification of the horizontal vestibulo-ocular reflex of rabbits. Proc Japan Acad. 51: 716–20.

Ito M, Jastreboff PJ, Miyashita Y (1979) Adaptive modification of the rabbit’s horizontal vestibulo-ocular reflex during sustained vestibular and optokinetic stimulation. Exper Brain Res. 37: 17–30.

Kamigaki T, Fukushima T, Miyashita Y (2009) Cognitive set reconfiguration signaled by macaque posterior parietal neurons. Neuron. 61: 941–51.

Kamigaki T, Fukushima T, Tamura K, Miyashita Y (2012) Neurodynamics of cognitive set shifting in monkey frontal cortex and its causal impact on behavioral flexibility. J Cognit Neurosci. 24: 2171–85.

Kikyo H, Ohki K, Miyashita Y (2002) Neural correlates for feeling-of-knowing: an fMRI parametric analysis. Neuron. 36: 177–86.

Konishi S, Jimura K, Asari T, Miyashita Y (2003) Transient activation of superior prefrontal cortex during inhibition of cognitive set. J Neurosci. 23: 7776–82.

Konishi S, Nakajima K, Uchida I, Sekihara K, Miyashita Y (1998a) No-go dominant brain activity in human inferior prefrontal cortex revealed by functional magnetic resonance imaging. Eur J Neurosci. 10: 1209–13.

Konishi S, Chikazoe J, Jimura K, Asari T, Miyashita Y (2005) Neural mechanism in anterior prefrontal cortex for inhibition of prolonged set interference. Proc Natl Acad Sci USA. 102: 12584–88.

Konishi S, Asari T, Jimura K, Chikazoe J, Miyashita Y (2006) Activation shift from medial to lateral temporal cortex associated with recency judgements following impoverished encoding. Cereb Cortex. 16: 469–74.

Konishi S, Nakajima K, Uchida I, Kikyo H, Kameyama M, Miyashita Y (1999a) Common inhibitory mechanism in human inferior prefrontal cortex revealed by event-related functional MRI. Brain. 122: 981–91.

Konishi S, Kawazu M, Uchida I, Kikyo H, Asakura I, Miyashita Y (1999b) Contribution of working memory to transient activation in human inferior prefrontal cortex during performance of the Wisconsin Card Sorting Test. Cereb Cortex. 9: 745–53.

Konishi S, Hayashi T, Uchida I, Kikyo H, Takahashi E, Miyashita Y (2002) Hemispheric asymmetry in human lateral prefrontal cortex during cognitive set shifting. Proc Natl Acad Sci USA. 99: 7803–808.

Konishi S, Nakajima K, Uchida I, Kameyama M, Nakahara K, Sekihara K, Miyashita Y (1998b) Transient activation of inferior prefrontal cortex during cognitive set shifting. Nature Neurosci. 1: 80–84.

Konishi S, Morimoto H, Jimura K, Asari T, Chikazoe J, Yamashita K, Hirose S, Miyashita Y (2008) Differential superior prefrontal activity on initial versus subsequent shifts in naive subjects. NeuroImage. 41: 575–580.

Konishi S, Yoneyama R, Itagaki H, Uchida I, Nakajima K, Kato H, Okajima K, Koizumi H, Miyashita Y (1996) Transient brain activity used in magnetic resonance imaging to detect functional areas. Neuroreport. 8: 19–23.

Koyama M, Hasegawa I, Osada T, Adachi Y, Nakahara K, Miyashita Y (2004) Functional magnetic resonance imaging of macaque monkeys performing visually guided saccade tasks: comparison of cortical eye fields with humans. Neuron. 41: 795–807.

Koyano KW, Takeda M, Matsui T, Hirabayashi T, Ohashi Y, Miyashita Y (2016) Laminar module cascade from layer 5 to 6 implementing cue-to-target conversion for object memory retrieval in the primate temporal cortex. Neuron. 92: 518–29.

Leonesio RJ, Nelson TO (1990) Do different metamemory judgments tap the same underlying aspects of memory? J Experimen Psychol Learn Mem Cognit. 16: 464–67.

Maril A, Simons JS, Mitchell JP, Schwartz BL, Schacter DL (2003) Feeling-of-knowing in episodic memory: an event-related fMRI study. NeuroImage. 18: 827–36.

Marr D (1969) A theory of cerebellar cortex. J Physiol. 202: 437–70.

Marr D (1976) Early processing of visual information. Phil Trans Royal Soc London B, Biol Sci. 275: 483–519.

Marr D (1980) Visual information processing: the structure and creation of visual representations. Phil Trans Royal Soc London B, Biol Sci. 290: 199–218.

Marr D (1982) Vision: A Computational Investigation into the Human Representation and Processing of Visual Information. New York: Freeman.

Marr D, Poggio T (1976) Cooperative computation of stereo disparity. Science. 194: 283–87.

Matsui T, Koyano KW, Koyama M, Nakahara K, Takeda M, Ohashi Y, Naya Y, Miyashita Y (2007) MRI-based localization of electrophysiological recording sites within the cerebral cortex at single-voxel accuracy. Nature Meth. 4: 161–68.

Matsuzaki M, Ellis-Davies GC, Nemoto T, Miyashita Y, Iino M, Kasai H (2001) Dendritic spine geometry is critical for AMPA receptor expression in hippocampal CA1 pyramidal neurons. Nature Neurosci. 4:1086–1092.

Messinger A, Squire LR, Zola SM, Albright TD (2001) Neuronal representations of stimulus associations develop in the temporal lobe during learning. Proc Natl Acad Sci USA. 98: 12239–44.

Metcalfe J, Schwartz BL, Joaquim SG (1993) The cue-familiarity heuristic in metacognition. J Experimen Psychol Learn Mem Cognit. 19: 851–61.

Middlebrooks PG, Sommer MA (2011) Metacognition in monkeys during an oculomotor task. J Exp Psychol Learn Mem Cognit. 37: 325–37.

Milner B (1968) Visual recognition and recall after right temporal-lobe excision in man. Neuropsychologia. 6: 191–209.

Milner B (1972) Disorders of learning and memory after temporal lobe lesions in man. Clin Neurosurg. 19: 421–46.

Miyamoto K, Setsuie R, Osada T, Miyashita Y (2018) Reversible silencing of the frontopolar cortex selectively impairs metacognitive judgment on non-experience in primates. Neuron. 97: 980–89.

Miyamoto K, Osada T, Adachi Y, Matsui T, Kimura HM, Miyashita Y (2013) Functional differentiation of memory retrieval network in macaque posterior parietal cortex. Neuron. 77: 787–99.

Miyamoto K, Adachi Y, Osada T, Watanabe T, Kimura HM, Setsuie R, Miyashita Y (2014) Dissociable memory traces within the macaque medial temporal lobe predict subsequent recognition performance. J Neurosci. 34: 1988–97.

Miyamoto K, Osada T, Setsuie R, Takeda M, Tamura K, Adachi Y, Miyashita Y (2017) Causal neural network of metamemory for retrospection in primates. Science. 355: 188–93.

Miyashita Y (1988) Neuronal correlate of visual associative long-term memory in the primate temporal cortex. Nature. 335: 817–20.

Miyashita Y (1993) Inferior temporal cortex: where visual perception meets memory. Ann Rev Neurosci. 16: 245–63.

Miyashita Y (2004) Cognitive memory: cellular and network machineries and their top-down control. Science. 306: 435–40.

Miyashita Y (2019) Perirhinal circuits for memory processing. Nat Rev Neurosci. 20: 577–92.

Miyashita Y, Chang HS (1988) Neuronal correlate of pictorial short-term memory in the primate temporal cortex. Nature. 331: 68–70.

Miyashita Y, Hayashi T (2000) Neural representation of visual objects: encoding and top-down activation. Curr Opin Neurobiol. 10: 187–194.

Miyashita Y, Higuchi S, Sakai K, Masui N (1991) Generation of fractal patterns for probing the visual memory. Neurosci Res. 12: 307–11.

Miyashita Y, Ito M, Jastreboff PJ, Maekawa K, Nagao S (1980) Effect upon eye movements of rabbits induced by severance of mossy fiber visual pathway to the cerebellar flocculus. Brain Res. 198: 210–15.

Miyashita Y, Rolls ET, Cahusac PMB, Niki H, Feigenbaum JD (1989) Activity of hippocampal-formation neurons in the monkey related to a conditional spatial response task. J Neurophysiol. 61: 669–78.

Murray EA, Gaffan D, Mishkin M (1993) Neural substrates of visual stimulus association in rhesus-monkeys. J Neurosci. 13: 4549–61.

Nakahara K, Hayashi T, Konishi S, Miyashita Y (2002) Functional MRI of macaque monkeys performing a cognitive set-shifting task. Science. 295: 1532–36.

Naya Y, Sakai K, Miyashita Y (1996) Activity of primate inferotemporal neurons related to a sought target in pair-association task. Proc Natl Acad Sci USA. 93: 2664–69.

Naya Y, Yoshida M, Miyashita Y (2001) Backward spreading of memory-retrieval signal in the primate temporal cortex. Science. 291: 661–64.

Naya Y, Yoshida M, Miyashita Y (2003) Forward processing of long-term associative memory in monkey inferotemporal cortex. J Neurosci. 23:2861–2871.

Nelson TO (1984) A comparison of current measures of the accuracy of feeling-of-knowing predictions. Psychol Bull. 95: 109–33.

Nelson TO (1996) Consciousness and metacognition. Amer Psychol. 51: 102–16.

Nicholson C, Freeman JA (1975) Theory of current source-density analysis and determination of conductivity tensor for anuran cerebellum. J Neurophysiol. 38: 356–68.

Norman DA, Shallice T (1986) Attention to action: willed and automatic control of behavior. In Davidson RJ, Schwartz GE, Shapiro D, eds. Consciousness and Self-Regulation. New York: Plenum.

O’Craven KM, Kanwisher N (2000) Mental imagery of faces and places activates corresponding stimulus-specific brain regions. J Cogn Neurosci. 12: 1013–23.

Ogawa S, Lee TM, Kay AR, Tank DW (1990) Brain magnetic-resonance-imaging with contrast dependent on blood oxygenation. Proc Natl Acad Sci USA. 87: 9868–72.

Ogawa S, Tank DW, Menon R, Ellermann JM, Kim SG, Merkle H, Ugurbil K (1992) Intrinsic signal changes accompanying sensory stimulation: functional brain mapping with magnetic resonance imaging. Proc Natl Acad Sci USA. 89: 5951–55.

Ohbayashi M, Ohki K, Miyashita Y (2003) Conversion of working memory to motor sequence in the monkey premotor cortex. Science. 301: 233–36.

Okuno H, Tokuyama W, Li YX, Hashimoto T, Miyashita Y (1999) Quantitative evaluation of neurotrophin and trk mRNA expression in visual and limbic areas along the occipito-temporo-hippocampal pathway in adult macaque monkeys. J Comp Neurol. 408: 378–98.

Osada T, Adachi Y, Miyamoto K, Jimura K, Setsuie R, Miyashita Y (2015) Dynamically allocated hub in task-evoked network predicts the vulnerable prefrontal locus for contextual memory retrieval in macaques. PLoS Biol. 13: e1002177.

Sakai K, Miyashita Y (1991) Neural organization for the long-term memory of paired associates. Nature. 354: 152–55.

Sakai K, Watanabe E, Onodera Y, Itagaki H, Yamamoto E, Koizumi H, Miyashita Y (1995a) Functional mapping of the human somatosensory cortex with echo-planar MRI. Mag Reson Med. 33: 736–43.

Sakai K, Watanabe E, Onodera Y, Uchida I, Kato H, Yamamoto E, Koizumi H, Miyashita Y (1995b) Functional mapping of the human color-center with echo-planar magnetic-resonance-imaging. Proc Royal Soc B, Biol Sci. 261: 89–98.

Schacter DL (1987) Memory, amnesia, and frontal lobe dysfunction. Psychobiology. 15: 21–36.

Schacter DL (1998) Memory and awareness. Science. 280: 59–60.

Scoville WB, Milner B (1957) Loss of recent memory after bilateral hippocampal lesions. J Neurol Neurosurg Psychiat. 20: 11–21.

Sekihara K, Nagarajan S, Poeppel D, Miyashita Y (1999a) Time-frequency MEG-MUSIC algorithm. IEEE Trans Med Imaging. 18: 92–97.

Sekihara K, Poeppel D, Marantz A, Koizumi H, Miyashita Y (1997) Noise covariance incorporated MEG-MUSIC algorithm: a method for multiple-dipole estimation tolerant of the influence of background brain activity. IEEE Trans Bio-Med Engin. 44: 839–47.

Sekihara K, Poeppel D, Marantz A, Koizumi H, Miyashita Y (1998a) Comparison of covariance-based and waveform-based subtraction methods in removing the interference from button-pressing finger movements. Brain Topogr. 11: 95–102.

Sekihara K, Poeppel D, Marantz A, Koizumi H, Miyashita Y (1999b) MEG spatio-temporal analysis using a covariance matrix calculated from nonaveraged multiple-epoch data. IEEE Trans Bio-Med Engin. 46: 515–21.

Sekihara K, Nagarajan SS, Poeppel D, Marantz A, Miyashita Y (2001) Reconstructing spatio-temporal activities of neural sources using an MEG vector beamformer technique. IEEE Trans Bio-Med Engineer. 48: 760–71.

Sekihara K, Nagarajan SS, Poeppel D, Marantz A, Miyashita Y (2002) Application of an MEG eigenspace beamformer to reconstructing spatio-temporal activities of neural sources. Human Brain Map. 15: 199–215.

Sekihara K, Poeppel D, Marantz A, Phillips C, Koizumi H, Miyashita Y (1998b) MEG covariance difference analysis: a method to extract target source activities by using task and control measurements. IEEE Trans Bio-Med Engin. 45: 87–97.

Sekihara K, Nagarajan SS, Poeppel D, Miyauchi S, Fujimaki N, Koizumi H, Miyashita Y (2000) Estimating neural sources from each time-frequency component of magnetoencephalographic data. IEEE Trans Bio-Med Engin. 47: 642–53.

Setsuie R, Tamura K, Miyamoto K, Watanabe T, Takeda M, Miyashita Y (2020) Off-peak 594-nm light surpasses on-peak 532-nm light in silencing distant ArchT-expressing neurons in vivo. iScience. in press.

Shields WE, Smith JD, Washburn DA (1997) Uncertain responses by humans and rhesus monkeys (Macaca mulatta) in a psychophysical same-different task. J Experimen Psychol Gen. 126: 147–64.

Shimamura AP (1995) Memory and frontal lobe function. In Gazzaniga MS, ed. The Cognitive Neurosciences. Cambridge, MA: MIT Press, 803–13.

Sidtis JJ, Volpe BT, Holtzman JD, Wilson DH, Gazzaniga MS (1981) Cognitive interaction after staged callosal section—evidence for transfer of semantic activation. Science. 212: 344–46.

Smith JD (2009) The study of animal metacognition. Trends Cogn Sci. 13: 389–96.

Squire LR (2006) Lost forever or temporarily misplaced? The long debate about the nature of memory impairment. Learn Mem. 13: 522–29.

Squire LR, Slater PC, Chace PM (1975) Retrograde-amnesia—temporal gradient in very long-term memory following electroconvulsive therapy. Science. 187: 77–79.

Squire LR, Zola-Morgan S (1991) The medial temporal lobe memory system. Science. 253: 1380–86.

Squire LR, Wixted JT (2011) The cognitive neuroscience of human memory since H.M. Ann Rev Neurosci. 34: 259–88.

Stuss DT, Benson DF (1984) Neuropsychological studies of the frontal lobes. Psychol. Bull. 95: 3–28.

Takeda M, Naya Y, Fujimichi R, Takeuchi D, Miyashita Y (2005) Active maintenance of associative mnemonic signal in monkey inferior temporal cortex. Neuron. 48: 839–48.

Takeda M, Koyano KW, Hirabayashi T, Adachi Y, Miyashita Y (2015) Top-down regulation of laminar circuit via inter-area signal for successful object memory recall in monkey temporal cortex. Neuron. 86: 840–52.

Takeuchi D, Hirabayashi T, Tamura K, Miyashita Y (2011) Reversal of interlaminar signal between sensory and memory processing in monkey temporal cortex. Science. 331: 1443–47.

Tamura K, Takeda M, Setsuie R, Tsubota T, Hirabayashi T, Miyamoto K, Miyashita Y (2017) Conversion of object identity to object-general semantic value in the primate temporal cortex. Science. 357: 687–92.

Tanaka K (1996) Inferotemporal cortex and object vision. Ann Rev Neurosci. 19: 109–39.

Tokuyama W, Okuno H, Hashimoto T, Xin Li Y, Miyashita Y (2000) BDNF upregulation during declarative memory formation in monkey inferior temporal cortex. Nature Neurosci. 3: 1134–42.

Tokuyama W, Okuno H, Hashimoto T, Li YX, Miyashita Y (2002) Selective zif268 mRNA induction in the perirhinal cortex of macaque monkeys during formation of visual pair-association memory. J Neurochem. 81: 60–70.

Tomita H, Ohbayashi M, Nakahara K, Hasegawa I, Miyashita Y (1999) Top-down signal from prefrontal cortex in executive control of memory retrieval. Nature. 401: 699–703.

Tulving E (1985) Elements of Episodic Memory. New York: Oxford University Press.

Van Essen DC, Glasser MF (2018) Parcellating cerebral cortex: how invasive animal studies inform noninvasive mapmaking in humans. Neuron. 99: 640–63.

Yoshida M, Naya Y, Miyashita Y (2003) Anatomical organization of forward fiber projections from area TE to perirhinal neurons representing visual long-term memory in monkeys. Proc Natl Acad Sci USA. 100: 4257–62.

Dale Purves

BORN:

Philadelphia, Pennsylvania

March 11, 1938

EDUCATION:

Yale University, BA (1960)

Harvard Medical School, MD (1964)

APPOINTMENTS:

Intern in Surgery, Massachusetts General Hospital (1964–1965)

Peace Corps Physician, Venezuela (USPHS) (1965–1967)

Assistant Resident in Surgery, Massachusetts General Hospital (1967–1968)

Resident in Neurosurgery, Massachusetts General Hospital (1968–1969)

Postdoctoral Fellow, Department of Neurobiology, Harvard Medical School (1968–1971)

Postdoctoral Fellow, Department of Biophysics, University College London (1971–1973)

Assistant Professor–Professor, Department of Physiology and Biophysics, Washington University School of Medicine (1973–1985)

Professor of Neurobiology, Department of Anatomy and Neurobiology, Washington University School of Medicine (1985–1990)

Chair, Department of Neurobiology, Duke University (1990–2002)

George Barth Geller Professor, Department of Neurobiology, Duke University (1990–2013)

Director, Center for Cognitive Neuroscience, Duke University (2003–2009)

Director, Neuroscience and Behavioral Disorders Program, Duke-NUS Graduate Medical School (2009–2013)

Executive Director, A*STAR Neuroscience Research Partnership (2009–2012)

George B. Geller Professor of Neurobiology, Emeritus and Research Professor, Duke Institute for Brain Sciences (2013–present)

HONORS AND AWARDS (SELECTED)

Mathilde Solowey Award in Neuroscience (1979)

Alexander Forbes Lectures, Grass Foundation, MBL (1983)

Camillo Golgi Award Lecture (FIDIA) (1988–1989)

Election to National Academy of Sciences (1989)

Grass Lecture, Society for Neuroscience (1990)

Lezioni Lincee Award Lectures, Accademia Nazionale dei Lincei, Italy (1992)

Election to the Institute of Medicine (1996)

Election to the American Academy of Arts and Sciences (1999)

Although Dale Purves is known for his earlier work on neural development and synaptic plasticity, his research during the last 20 years has sought to explain why we see and hear what we do, focusing on the visual perception of lightness, color, form, and motion, and the auditory perception of music and speech. The goal of this work has been to establish an operating principle for nervous systems based on the fact that sensory systems cannot measure physical reality directly and therefore must use accumulated experience to generate the basic qualities we perceive. This understanding of neural function runs counter to the widely held view that sensory information is used to compute models of reality.

Dale Purves

Childhood

I was born in 1938, the second child and first son of an upper middle-class Philadelphia family. My long-suffering father was a businessman saddled with an impossibly neurotic wife and four children who were in various ways a difficult lot. Although successful in business, he was deeply interested in science, math, and music.

My father’s burdens were not made any lighter by me. As a young child I was a mess, refusing to go to preschool and throwing tantrums at the prospect of social engagements. There were attempts to establish a diagnosis and as a four- or five-year-old I remember seeing a psychiatrist. Nothing came of this effort and by first grade I seemed to be coming around. Further restoration to relative normalcy came when my father, at the age of 45, resigned his vice presidency at the Stetson Hat Company and took a job setting to rights a steel company in Mexico City at the behest of a New York financier. Our new lives in Mexico turned me from a cranky kid into a more or less typical neighborhood boy who was good at tops, marbles, yo-yos, and sports and who played with five or six local children on the unpaved street in front of our house. As a second grader, I quickly learned Spanish and was a good and enthusiastic student at the bilingual school I attended. Adding to this time of general contentment was my father’s enthusiasm for wide-ranging travels in Mexico. These halcyon days came to an end, however, when my dad was fired for siding too often with the Mexican workers rather than management (he was a small “d” democrat through and through). We returned to Philadelphia in 1949, where I rejoined my class at the Germantown Friends School at the end of fifth grade.

Anxiety about my father’s new job as a founding partner of a management consultant firm was palpable. Adding to his worries my mother had a “nervous breakdown” and left for the Institute of Living in Hartford where she stayed for several months. I soon turned into a worrisome teenager given to periods of depression, general misbehavior, and grades that reflected all this. The saving grace was the very good school I attended, a group of new friends, and the gradual realization that science was interesting. Having no concept of scientific practice outside the classroom, I gravitated toward medicine as a profession that might mix science, excitement, financial reward, and social status. To test these waters, when I was 16 or 17, I spent the summer living with my aunt and uncle in Connecticut working as an orderly in the local hospital. Despite emptying bedpans, shaving male abdomens in preparation for surgery, and cleaning up after the occasional autopsy, the ambience of medicine was appealing. The obvious respect of patients and nurses for the doctors encouraged the sense that medicine was a good bet. And my high school courses in chemistry and physics under an excellent teacher began to restore my academic credibility. It was soon clear that I would head to college as a premed student.

College

When it came to choosing a college, I gave the issue very little thought. My father, presumably having seen too many Princeton products in Philadelphia society, indicated that if this was my choice, I would have to pay my way. That left Harvard and Yale. Harvard had a reputation for being effete and Yale appealed to me as more “manly.” My ignorance about what would be facing me and my unsuitability for playing the proverbial Jack Armstrong All American Boy role was profound.

When I matriculated at Yale in the fall of 1956, I quickly discovered some unhappy consequences of my choice. My class of about 1,000 was frontloaded with young men (it was a decade before women were admitted) from New England prep schools who knew the ropes and came with a cohort of friends (or at least knew who their enemies were). I knew no one. In my zeal to “belong” at Yale, I had indicated on my application I would just as soon have WASP roommates. As a reward, I was assigned two lily white Protestants with whom I had nothing in common and one of whom was patently weird. Things got worse when my high school girlfriend at the time, a first-year student at Mount Holyoke, unceremoniously dumped me. I was also brought up short by a failing grade on my first chemistry test. None of this helped my mental status. I should have sought counseling but did not want to be “stigmatized.” The final straw in my comeuppance at Yale was “rushing” a fraternity only be turned down despite family connections. Having failed miserably in my misguided effort to become a proper Yale man, I told my father that I was quitting college to join the Army. He convinced me over a somber lunch at the Century Club in New York (to which he had been recently been elected) that this was not a good idea. Although his new club was not the best locus for the meeting, perhaps the subtext was that if he could succeed after being fired in Mexico, I should not quit so easily. Thoroughly beaten, I returned to New Haven.

The aspect of Yale that had little of my attention in high school—its academic excellence—eventually began to sink in. Although I had failed my first test in freshman chemistry, I had buckled down and ended the semester with the top grade. Deciding to work hard (I was a premed after all) was the first sensible choice I made at Yale. The second was to major in philosophy. I had a knack for thinking more or less logically and my philosophy professors seemed to recognize that they’d hooked a live one. By the time I was a rising junior, I had become a committed intellectual and by the end of my junior year, my early failures had dimmed, although they certainly were not forgotten. In the end, I graduated 1 of 15 students awarded a degree summa cum laude. The most important thing I had learned at Yale, however, was that I was capable of incredible stupidity at an age when I should have understood myself and the world better. When it came time to apply to medical school, I gave the matter more thought than I had given what college to attend, but it didn’t take much investigation to recognize that Harvard topped the list. I applied for early admission and was accepted with the idea that, given my interest in philosophy, psychiatry might be a good specialty for me.

Medical School

Although “enjoyable” is not the right adjective to describe medical school, I felt for the first time that I was in the right place with the right colleagues and the right teachers doing something serious. Given my potential interest in psychiatry, I was especially attuned to what I might get out of our first-year course on the nervous system. I assumed it would be the beginning of a new effort to learn about brain biology in a more serious way than I had managed as an undergraduate, and so it was. The senior member of the neuroscience teaching faculty was Stephen Kuffler, then in his early 50s and already a central figure in neuroscience. Having recently arrived at Harvard from Johns Hopkins, he had presciently promoted to faculty status two postdoctoral fellows who had been working with him, David Hubel and Torsten Wiesel. They were then 34 and 36, respectively. He had also hired David Potter and Ed Furshpan, two even younger neuroscientists who had recently finished fellowships in Bernard Katz’s lab at University College London. The last of his initial recruits was Ed Kravitz, who at 31 had just gotten his doctorate in biochemistry from the University of Michigan. Furshpan and Potter taught us how nerve cell signaling worked, Kravitz taught us neurochemistry, and Hubel and Wiesel taught us about the organization of the brain (or at least the visual part of it, which was their bailiwick). Kuffler gave a pro forma lecture or two, but teaching was not his strong suit and he had the good sense to let his new young faculty carry the load.

Unlike teaching us about nerve cells and the mechanisms of the action potential and synaptic transmission, conveying some idea of what the brain is actually doing was a difficult task in 1961. Hubel and Wiesel dealt with this challenge by simply telling us about their work on the organization and function of the visual part of brain. It was not unusual for professors to cop out by telling us what they had been doing in their labs rather going to the effort of putting together a broader and more useful introduction to some subject. But in this case, it was obvious that what Hubel and Wiesel were trying to do was extraordinary. Based on what Kuffler had established in the retina, they were exploring the properties of visual neurons in progressively higher stations in the visual system of the cat, and this was the work that we students heard about as an introduction to the brain.

Despite the excellence of these extraordinary teachers, much of what I had learned from them was soon forgotten. It was not lost on me, however, that the group Kuffler had put together represented a remarkable collection of scientists working on problems that were importantly connected to my conception of what I might eventually do. But all of us had to cope with the courses or rotations that were coming next, and I was still wedded to the idea of pursuing psychiatry.

Disillusion with Psychiatry

My conviction that psychiatry was a good choice began to wane as my knowledge of the field waxed over the next few years. The first disillusion came during the summer after my first year in medical school, not long after the course that Kuffler and his recruits had given us. There was a summer break between first and second year, and we were encouraged to spend the summer working in one of the research labs at the school. Our pharmacology course during the first year included several lectures on psychoactive drugs and, given my inclination toward psychiatry, I thought working with the professor who had presented this material made sense. But the only significant result by the end of my research summer was the demise of an unconscionable number of rabbits.

The experience that disabused me once and for all about the merits of pursuing psychiatry, however, was my first clinical rotation. Although we had some instruction in psychiatric diseases during the second year of medical school, our exposure to the psychiatry wards did not come until the third year. My rotation in clinical psychiatry was at the Massachusetts Mental Health Center, housed in a ramshackle building a few blocks from the medical school. Psychiatry at Harvard in 1963, and at the Mass Mental Health Center in particular, was one of the last strongholds of the Freudian analytical treatment of severely disturbed patients, and the preceptor during my rotation was a psychiatrist who believed strongly in this concept. Sitting through his psychoanalytically based interrogatories of psychotic patients eroded what little remaining faith I had that psychiatry was the field for me. The final blow came one Saturday afternoon when another student and I found a patient who had hung himself in one of the bathrooms. The usual resuscitative procedures were far too late to help, but the psychiatry resident in charge seemed to have less knowledge about how to proceed than we did. The message was clear: psychiatrists were not real doctors, and being a real doctor loomed large for me.

Surgery

Anyone navigating the rigors of medical school gravitates toward one or more role models to provide inspiration and, having given up on psychiatry, I began to look elsewhere. Harvard abounded in potential models and one of most charismatic was Francis Moore, the chief of surgery at the Peter Bent Brigham Hospital, where I did my third-year rotation in surgery. Moore was then in his early fifties and already legendary. As an undergraduate at Harvard, he had been president of both the Harvard Lampoon and the Hasty Pudding Club, and was appointed surgical chief at the Brigham at the age of 32. He was a member of the team that had performed the first successful organ transplant in 1954 and had written a widely respected book in 1959 called The Metabolic Care of the Surgical Patient that underscored his status as a physician-scientist. Holding retractors as a student assistant while Moore exercised his jocular authority and surgical skills turned me in a new direction. I decided then and there that I would train in general surgery.

After some further electives in surgery during my last year in medical school, I applied for a residency in general surgery at the Massachusetts General Hospital, then considered the top program despite Moore’s preeminence at the Brigham. I was accepted and started my surgical internship in the summer of 1964. It is hard to believe in today’s atmosphere of managed care, oversight by insurance companies, and litigation that we “doctors in training” were largely unsupervised. The wards were always filled with patients who could not afford a private doctor, and for better or worse, they were entirely our responsibility (“better” was around-the-clock care by dedicated young doctors; “worse” was our lack of experience).

The chief resident I worked under during the first part of my internship year was Judah Folkman. Like Moore at the same age, Folkman was thought to be destined for great things, as turned out to be the case. At 34, Folkman was named surgeon-in-chief at Boston’s Children’s Hospital, becoming along with Moore one of the youngest professors ever appointed at Harvard Medical School. He became justly famous in the early 1970s for pioneering a novel way of treating cancer by inhibiting blood vessel growth, and at 46, he gave up this appointment as a professor of surgery to pursue basic research on angiogenesis. Folkman was perhaps the most impressive individual I had ever met. Physically slight, already balding, with a great beak of a nose, he dominated in any setting by intelligence, wit, and force of character. The residents universally looked up to him not simply because he was surgically skilled and supremely smart, but because he radiated confidence and integrity that made everyone under him deal better with the daily strife and our inevitable mistakes.

For me, however, working under Folkman that year had another effect. Any competitive individual continually measures himself or herself against the qualities and talents of peers. Although as chief resident Folkman was far advanced from an intern struggling to learn the rudiments of the trade, he was only five years ahead of me, and I had to envision myself in his role in the near future. The comparison was discouraging. I didn’t see him as necessarily smarter or feel that I could never reach his level of technical skill (although I had serious doubts on both counts). What dismayed me was his obvious passion for the craft, which I had already begun to realize I lacked. The recognition that, like psychiatry, a life in general surgery was probably not my calling came at 2 or 3 in the morning when Folkman was trying to make an apparatus to dialyze a patient dying from kidney failure using an old washing machine and other odds and ends he had collected from a hospital storeroom. Although the effort failed, I realized that I would not have made it and that this disqualified me from trying to follow the footsteps of figures like Folkman and Moore.

Venezuela

Thus, I needed to invent another path to the future. This time I was given some breathing room by the war in Vietnam. By 1965, virtually all physicians in training were drafted, and my notice arrived about halfway through my internship. Given my concern over the prospects of a career as a general surgeon, being drafted was not entirely unwelcome. There was another reason as well. Since childhood I had suffered periods of depression. A year of psychoanalysis during my last year of med school had not helped, although it confirmed my conviction that psychiatry was not something I wanted to pursue. I ended my internship year without a clear plan and clinically depressed. The bright side was that I would now have two years of enforced service to pull myself together and sort things out.

Despite the rapidly escalating war in Vietnam, the options for physicians drafted in 1965 were still broad. I could join one of the armed services; seek deferment for further surgical training; apply for a research position at the National Institutes of Health; join the Indian Health Service; or apply to become a Peace Corps physician. This last option meant serving two years in the Public Health Service taking care of Peace Corps volunteers in one of many countries around the world. Given my uncertain frame of mind about what to do next, my total lack of interest in research, and my opposition (along with almost everyone else I knew) to the war, the Peace Corps seemed the best bet. And so, after a few weeks of remedial training in tropical medicine at the Centers for Disease Control in Atlanta, I arrived in Venezuela in July 1965.

As it turned out, the Peace Corps was a good choice. The volunteers that I and another young doctor had to look after were an inspiring bunch who demonstrated all the good things about Americans and American democracy of that era. Since I spoke Spanish as the result of living in Mexico as a kid, I could travel easily and interact well with local doctors. And Venezuela in the 1960s was a beautiful, prosperous, and relatively progressive country. From the medical perspective, the job was easy, serving as general practitioner to about 400 sometimes difficult to reach but generally interesting and healthy young adults. My life in South America was in every way a radical change, and for the first time since college, I had time to think rather than simply meet the demands of medical training.

I read widely, including a lot of books on science that I had not been exposed to as an undergraduate majoring in philosophy or as a medical student and intern with no spare time. One of the books I picked up while rummaging around the American Bookstore in Caracas was The Machinery of the Brain by Dean Wooldridge. Having become wealthy in the aerospace industry, Wooldridge had resigned in 1962 to pursue his passion for basic science. The Machinery of the Brain, published in 1963, was his first effort. Although I was passingly familiar with much of the content, his lucid synthesis of the information I had learned about the brain as a med student got me thinking about issues that I had been keenly interested in but had lost touch with as a prospective surgeon. Wooldridge’s book was modest and provocative and got me thinking about the nervous system once again.

Because I had two years to mull things over before I was scheduled to resume my post as a resident in general surgery at Mass General, there was no rush to sort out my thoughts about a career that might combine an interest in the brain with my training as a physician. I eventually concluded that the most logical course under the circumstances was neurosurgery. In addition to the internship year I had already completed, becoming a neurosurgeon required another year of general surgery that awaited me on my return to Boston, so I was already well along this path. Neurosurgery, I thought, would combine my earlier and now reviving interest in the nervous system, which I had pushed aside as a result of my disillusion with psychiatry.

And so, soon after returning to Boston in the summer of 1967, I asked William Sweet, the head of neurosurgery at Mass General, if I could join his program when I completed my second year of general surgery. He agreed, and I was thus to start formal training in neurosurgery the next year. Despite the logic of this plan, within a few months of my return from the Peace Corps, I began to have doubts about what had seemed, in principle, a good marriage of interests and training up to that point. Sweet was no Francis Moore or Judah Folkman, and his colleagues on the neurosurgery faculty at the time were not much more inspiring. In fact, what they did on a daily basis was not, when I experienced it firsthand, all that interesting. In contrast to my abstract enthusiasm for exploring the brain, the actual operations were long and tedious, and the outcomes all too often a foregone and unhappy conclusion.

As I worried increasingly about the prospect of neurosurgery, my thoughts kept turning back to the young neurobiologists Kuffler had brought to Harvard in the late 1950s and the impression they had made on me. Thus, in the winter of 1967, I found myself back at Harvard Medical School in the office of David Potter, who had taught us about action potentials and synaptic transmission six years earlier. I remembered Potter as the most approachable of the group and sought him out for advice about whether research in neuroscience might be a reasonable option. He listened with apparent interest as I summarized my concerns with neurosurgery and my interest in perhaps giving research in neuroscience a try. On the face of it, my arguments were feeble: the sum total of my research experience was the disastrous summer spent in a pharmacology lab, and my desire to try research had been reached largely by excluding other options. Despite the weakness of my case, Potter said he would think about my situation, and we agreed to meet again. In the meantime, I asked Sweet if I might take my first year in the neurosurgery program as a research fellow, and, primarily because of scheduling issues, he agreed.

When I returned to Potter’s office a couple of weeks later, he considered my intention to try research plausible enough, and suggested that I contact John Nicholls to see if he could take me on as a fellow. Nicholls was working at Yale as an assistant professor and had just been recruited to Harvard by Kuffler. I was disappointed because I had no idea who Nicholls was and had hoped to work with Potter himself or perhaps Hubel and Wiesel. I was even more dismayed when Potter told me that Nicholls was working on the nervous system of the leech. I had no idea what any of the neurobiology faculty was doing then or why, but it was difficult to imagine how the leech was pertinent to my ill-formed ambition to become a neuroscientist.

In fact, the suggestion was a good one. I was somewhat reassured when Potter told me that Nicholls had been a graduate student with Bernard Katz in the late 1950s after he had completed his medical training in London; that he had been a fellow in Kuffler’s lab thereafter; and that his work on the leech was widely regarded as an outstanding example of what was then a new approach to understanding neural function—namely, studying the nervous systems of simple invertebrates. More to the point, Potter went on to say that because Nicholls would be starting up a new lab at Harvard, he would probably welcome a fellow, even one whose experience in neuroscience was nil. Thus, I wrote to John who invited me to visit him at Yale.

And so on a bleak Saturday in February 1968, Shannon Ravenel, whom I was engaged to marry later that spring, and I drove down to New Haven. I had met Shannon, an up and coming editor at Houghton Mifflin, while still in med school and we had had an on-again off-again relationship that, happily for me, had been on-again since I returned from Venezuela. Yale Medical School was unimpressive (I had never actually been there, even though it was only a few blocks from the residential college where I had lived as an undergraduate). John’s lab was equally nondescript, and it was quickly evident that John himself had a complex personality that might not be a good fit with my own. Driving back to Boston that night, Shannon pointedly asked me if I really wanted to make this change in the light of all the evidence that I would be sailing into uncharted waters. Even though my confidence in answering was minimal, there were several reasons that argued for seeing it through: Potter’s word that Nicholls was a good mentor; the lack of obvious options if I wanted to try research; and a determination on my part to do something that might ignite a passion for understanding the brain. And I could always go back to the neurosurgery program at Mass General if the research year failed. Thus, a few days after getting back to Boston, I called John to say that I was willing if he was. Shannon and I married in May, I finished my year of residency in June, and after spending that summer in Vietnam under the auspices of a Boston-based antiwar group selecting war-injured children for treatment in the United States, at age 30, I began my life as a neuroscientist.

Postdoc at Harvard

Although the Department of Neurobiology at Harvard was probably the best place I could have tested the merits of this new choice, the transition was not easy. For the previous four years, I had been a practicing doctor: whether in Boston, Venezuela, or Vietnam, I had had all the responsibilities and respect that being a physician entails. Suddenly, I was a superannuated student on the bottom rung of the ladder; even the two beginning graduate students in the department knew much more science than I did, and they seemed a lot smarter to boot. The stress was of a very different kind than I had experienced during the years I had worked in surgery, but the first year I spent in John’s lab was nearly as trying. There was, however, a fundamental difference: despite my ignorance and well-justified sense of inferiority, I finally loved what I was doing. For the first time in years, I worked hard not because I had to, but because I wanted to.

The approaches to the brain and neural function that Kuffler and his young faculty were spearheading when I was a student in 1961 had flowered by the time I returned as a fellow in 1968. The question that always confronts the next generation of scientists—Nicholls and the rest of the faculty in this case—was what to go after next. One answer to the question had already been supplied by Kuffler’s study of the retinal cell responses at Hopkins, the impetus for the work on vision being carried on by David Hubel and Torsten Wiesel. By the time I arrived back at Harvard as a fellow, they were already well on the way to the dominant position in brain physiology that they would hold for the next several decades. Another aspect of Kuffler’s work had stimulated a quite different direction that seemed equally promising, and this had determined the work John Nicholls was doing when I joined his lab. Following his graduate work with Katz, John had joined Kuffler’s lab as a fellow in 1962, and they had worked together to understand the function of glial cells using the leech nervous system as a model. By the time John left Harvard to join the faculty at Yale, the work on glia had finished, but he continued using the leech as a simple system in which to explore neuronal circuitry in relation to behavior. The opinion held by Nicholls and many other neuroscientists when I joined his lab in the fall of 1968 was that a logical next step in moving beyond the established understanding of neural signaling would be to focus on invertebrate nervous systems to fathom basic principles of neural function. The prospect of relating the function of identified nerve cells to some bit of behavior was attractive and that was the topic I threw myself into as a novice neuroscientist. Absorbing the rationale for exploring the nervous system in this way, and learning the required methods and their scientific basis as a beginner with no background in electronics, mathematics, or anything much else that was relevant, led to many low moments. But the work was conceptually and technically fascinating, and I was buoyed by the fact that a lot of obviously smart people thought this was a good way to explore how vastly more complex mammalian brains might operate.

As Potter had promised, Nicholls was indeed a good mentor and, after two years of working diligently to understand how sensory and motor neurons in the leech nervous system were related, I had written two papers of modest interest that were published in the Journal of Physiology, the journal of record in those days (an output of one detailed paper a year was typical). But despite my appreciation of his teaching, John and I did not get on particularly well. In addition to what we were doing on a daily basis, I wanted to discuss the broader issues that had always interested me about brains and their function, and John didn’t have much stomach for that sort of thing. He told me that as a graduate student, he had been terrified of Katz and the prospect of his failing in his eyes; perhaps as a result, he seemed unwilling to think in grander terms that Katz might have thought silly. By mutual consent, John and I agreed that I would spend the third year of my fellowship in Kuffler’s lab (I had already told William Sweet I would not be returning to the neurosurgical program), working with Kuffler’s senior collaborator at the time, Jack McMahan. Jack and I had already been looking at the anatomy of leech neurons revealed by the injection of a fluorescent dye that had been developed as a sort of sideline by Ed Kravitz. Jack, a terrific neuroanatomist, was about my age but years ahead of me as a neuroscientist and about to be named to the faculty. We got along famously and had a wonderful time that year, during which he taught me how to do electron microscopy.

During that year, Bernard Katz visited Kuffler’s lab, as he regularly did. The friendship and mutual respect between the two first formed in Australia had resulted in a small but steady flow of young neuroscientists between Boston and London, and it was clear that working in Katz’s orbit would be a fine next step for me. Although I had learned a lot of neuroscience in my three years as a fellow, I had started from scratch. It seemed foolhardy not to seek more training before going off on my own. The need was all the more obvious because I had decided that working on invertebrate nervous systems was not what I wanted to pursue. And so I asked John and Steve if they would support my case to Katz, which they did. Harvard offered a generous traveling fellowship that would support two years of study abroad, and in the summer of 1971, Shannon and I set off for London with our one-year-old daughter. What I would pursue in Katz’s small Department of Biophysics at University College had not been specified, but I was by then sure that I had found my professional niche.

Postdoc at University College

Although Bernard Katz’s impact on the course of neuroscience was as at least as great as Kuffler’s, the styles of the two men were entirely different. Whereas Kuffler’s modus operandi was quintessentially eclectic—he would work on a project with a collaborator or two for three years and then move on to an entirely different problem—Katz was a scientific bulldog. He had seized on the fundamental problem of chemical synaptic transmission in the late 1940s and never let it go. And whereas Kuffler was, superficially at least, an extroverted democrat, Katz was reserved and to some degree an autocrat.

As a result of these personal contrasts, as well as the cultural distinctions between the way science was practiced then in the United States and the United Kingdom, Katz’s Department of Biophysics at University College London (UCL) was about as different from the Department of Neurobiology at Harvard as one could imagine. The labs were on the upper floors of one of the old UCL buildings on Gower Street that ran the length of a long London block and housed most of the basic science departments. The rooms of the five faculty members in the department were comfortable but modest, and the surfeit of furnishings, equipment, and supplies that I had been used to in Boston was nowhere in evidence. Even Katz’s lab was outfitted with equipment that would have been consigned to storage at Harvard, and his small office contained the same simple furniture that must have been used by A. V. Hill when he was director in the 1930s. Among other things, all this made clear to me that superb science could be done in modest circumstances.

The students and fellows in Katz’s domain (about a half dozen of us) were in labs along a short corridor on the floor that included Katz’s lab at one end, as well as the supply room and a machine shop. For most of the 1960s, Katz had collaborated with Ricardo Miledi, an extraordinarily talented experimentalist who was Katz’s executive lieutenant and the most prominent of the other faculty members. Miledi had a smaller lab adjacent to Katz’s where he pursued his own projects with a couple of fellows in addition to his ongoing work with Katz. The other faculty members were on the floor above and included Paul Fatt, a brilliant but eccentric physiologist who had collaborated with Katz in the early 1950s in discovering the “quantal” nature of chemical synaptic transmission; Sally Page, an electron microscopist; and Rolf Niedergerke, another very good biophysicist and a disciple of Andrew Huxley who was working on the properties of heart muscle.

Although I expected to work on a project that would explicitly tap into the expertise and interests of Katz, Miledi, and the others in this new environment, I had no idea when I arrived of what the options in London might actually be. The year I had just spent working with Jack McMahan in Kuffler’s lab had been very valuable technically. But my work with Jack had not presented a problem that seemed worth pursuing. Having already soured on the nervous systems of simple invertebrates like the leech, the question for me when I matriculated in Katz’s department was what general direction would make sense in that environment and provide me with a starting point for my own research in the academic job I would have to secure when my two-year fellowship ended.

The first day I came to work after getting settled in our flat in Hampstead, Katz invited me into his office to discuss what I might do. Katz, then 60, was austere but certainly not the terrifying figure John Nicholls had described. He listened patiently to my ill-formed ideas and suggested that I should take my time in deciding on a particular project. He mentioned that another postdoc, Bert Sakmann, happened to be at loose ends and was also thinking about what to do next. Accordingly, I met Bert later that day and we chatted about the possibility of working together.

Bert had been medically trained in Tübingen and later in Munich, where he claimed he had gone in pursuit of the fellow medical student he eventually married. In the course of his medical education in Munich, Bert had spent three years carrying out research on the visual system with Otto Kreutzfeldt. Like many of us brought up scientifically in that era, Bert thought that working directly on the visual system or some other part of the brain was a rather daunting prospect and, with Kreutzfeldt’s help, had sought out further training with Katz to pursue a future working at the seemingly more tractable level of neurons and their synaptic interactions. We hit it off well because of our similar backgrounds, shared fascination with all aspects of neuroscience, and corresponding opinions about the odd cast of characters and their relationships in the Department of Biophysics. Although Bert was four years younger, we were both recently married, ambitious, and faced the need to land academic jobs when we finished our fellowships. Thus, we wanted to do something significant that would get our careers off and running. Our initial conversation made clear, however, that neither one of us had a very good idea about what that might be.

The issue that finally captured our attention, as well as that of many other neuroscientists at the time, was how neural activity affects synaptic interactions and neuronal connectivity. It had long been apparent that understanding how experience is encoded in the nervous system was a major challenge in neuroscience. Successfully addressing this issue would explain the way we and other animals learn, and unlike the mechanisms of neural signaling, this problem was far from being solved. Because the currency of experience in neural terms is the action potential, it had been assumed for decades that learning involves activity-dependent changes at synapses. Pursuing some aspect of how activity changes neural circuits thus seemed to us a worthy goal.

This general line of thinking had already motivated a lot of related work in other labs in the 1960s, and one of these was the lab of Per Andersen in Oslo. Andersen, like Kuffler and Katz, was a trainee of John Eccles, albeit many years later. A student of Andersen’s, Terje Lømo, had discovered a particularly long-lasting form of potentiation in the brains of rabbits in 1966, a topic he pursued with Tim Bliss, another fellow who had arrived in Andersens’s lab in Oslo in 1968. The phenomenon of long-term potentiation that Lømo and Bliss described in the hippocampus was rightly taken to be especially important. Lømo was a fellow in Katz’s department at the time Bert and I were considering what we might do, but he was about to leave to work further with Tim Bliss at Mill Hill in north London, where they pursued hippocampal potentiation and firmly established its importance. At University College, however, Lømo had worked on a different project with Jean Rosenthal, another fellow who had just left. Together they had shown that prolonged stimulation of a muscle changed the sensitivity of muscle fibers to the neurotransmitter acetylcholine. This effect suggested another way of exploring how activity could change the behavior of excitable cells. After some further discussion, Bert and I decided that following up on what Lømo and Rosenthal had done would be a fine way to better understand how activity could alter the properties of nerve and muscle cells and, in principle, store information derived from experience.

Our idea about a way to attack this issue was based on an odd fact that neurologists had known and used as a diagnostic tool for decades. When muscle fibers are denervated, they begin generating action potentials on their own (fibrillation). The origin and consequences of this spontaneous activity raised ways to examine the activity-dependent control of postsynaptic cell properties in muscles taken out of an animal and kept alive for a week or so in a Petri dish. In these circumstances, the spontaneous activity in individual muscle fibers could be monitored directly with a recording electrode, the levels of activity experimentally altered by electrical stimulation or a drug and the sensitivity of the fibers to neurotransmitter tested. Katz and Miledi agreed that this seemed to be a sensible project, and so for the next two years, we happily set about exploring these issues. Because neither we nor anyone else in the department knew how to go about this, we fiddled with various chambers, muscles, methods of stimulation, recording electrodes, and culture conditions until we got things to work. Eventually we could record for several days from single muscle fibers and watch their activity wax and wane as spontaneous action potentials or their absence in the fibrillating fibers altered their membrane properties and consequently their sensitivity to acetylcholine. We also stimulated the muscle artificially, showing that denervated fibers kept active never started to fibrillate, and they could be made to stop fibrillating if the spontaneous activity had been allowed to start. Although the results were in the end a modest contribution (another couple of good but rarely cited papers in the Journal of Physiology), Bert and I had a fine time being on our own and doing what we thought was interesting.

Katz gave the two manuscripts that Bert and I wrote up at the end of our time in the department his seal of approval and suggested we also show the papers to Andrew Huxley, who was in the Department of Physiology a few corridors away in the warren of UCL buildings. Huxley had been studying muscle contraction since the 1950s in work that was as impressive in its own way as what he had done with Alan Hodgkin on the action potential in the 1940s. Since our work concerned muscle fibers, Katz thought Huxley would be interested and might have useful criticisms. Huxley thought the papers more or less fine, but chastised us for having blacked out some noise around the oscilloscope traces with a marking pen, an innocuous bit of pre-Photoshop improvement of our figures that, for a purist like Huxley, was a cardinal sin.

Bert left London in 1973 to take up an assistant professorship in Goettingen, where within the year, he began a collaboration with Erwin Neher that eventually led to a Nobel Prize in Physiology or Medicine in 1991 for having developed patch clamping, a further step in understanding the basis of neural signaling that Hodkgin, Huxley, Katz, and Kuffler had done so much to advance in the preceding 30 years.

I also had to worry about getting a permanent job and what I would do when I did. While still at Harvard in 1970, I had met Carlton Hunt when, like Katz, he had come by to visit Kuffler. Cuy, who was then in his early fifties, had been Kuffler’s first fellow at Johns Hopkins and had spent four years collaborating with him. Together they had worked on stretch receptors in muscle fibers, a project typical of Kuffler’s nose for important problems. When I first ran into Cuy at Harvard, he had recently moved to Washington University from Yale and was in the process of building a Department of Physiology and Biophysics in St. Louis, having already put together excellent departments at the University of Utah and then at Yale (where as chair of physiology he had hired John Nicholls). Cuy was then—as always—a distinguished figure, and it was obvious that Steve and the rest of the faculty at Harvard liked him and admired the two departments he had already created. Whatever conversation we had then about future plans must have been quite tentative. I nonetheless took note that—if history and first impressions were any guide—Cuy would be an excellent person to work for.

I met Cuy again two years later in the summer of 1972 when he visited Katz at University College. Cuy had done a sabbatical year in Katz’s lab a decade earlier when he had taken a break from muscle spindles to study the effects on neurons of cutting their axons, thus interrupting the connection between the nerve cells and their targets. He was a great admirer of Katz, and took pains to visit whenever he was in England. Cuy took me to lunch to discuss what I had been doing and the possibility of joining his new department. We agreed over coffee that I would visit St. Louis later that fall to have a look. Although the trip in late October of 1972 included the few other places that had indicated some interest in hiring me, I liked St. Louis, Washington University, and the potential colleagues I met there. Washington University had a rich history of research in neuroscience, but most important, I felt I would be comfortable working in a department run by Cuy and that he would provide guidance to someone still relatively untutored in science and the ways of academia.

And so, with some difficulty, I convinced Shannon that St. Louis was the right place for us—or for me, she would no doubt wish to add—and we arrived in the Midwest on a sweltering day toward the end of the following summer.

Washington University

Given the need to teach the full range of physiology to the medical students, the Department of Physiology and Biophysics Cuy had put together included people who worked on the lung, kidney, and heart. Nonetheless, Cuy’s enthusiasms clearly favored neuroscience, and 6 or 7 of the approximately 15 faculty members were neuroscientists. In addition to me, the faculty included Carl Rovainen, who had been a graduate student with Ed Kravitz at Harvard and worked on the nervous system of the lamprey; Mordy Blaustein, who had been a postdoctoral fellow with Hodgkin at Cambridge and worked on the role of calcium ions in cell signaling; and Alan Pearlman and Nigel Daw, both of whom had been fellows in Hubel and Wiesel’s lab at Harvard and were continuing to work on the visual system.

Although my initial interests in neuroscience had been anything but reductionist, everything I had done over the preceding five years had been at a simple model systems level. Thus, I was ill prepared to launch into a project that focused on the structure and function of the brain. But I was at least determined to work on nerve cells in a mammal as a step in the right direction, and on problems that would have more pertinence to brain function and organization than the projects I had cut my teeth on.

While still in London, I had of course given some thought to the possibilities. With Jack McMahan, I had worked on autonomic ganglia, a staple of the work that was then going on in Kuffler’s lab. Studying these accessible collections of neurons and their connections with both the central nervous system and peripheral targets seemed a good compromise between plodding onward with some aspect of a model synapse like the neuromuscular junction and a more direct attack on some aspect of the brain, which I knew very little about. Autonomic ganglia had been the focus of many key studies of the nervous system since the middle of the 19th century and had set the stage for understanding neurotransmitter action at synapses and, ultimately, for Katz’s discoveries of the detailed mechanism of chemical synaptic transmission.

Whatever the merits of choosing the autonomic system, getting started in St. Louis depended on much more than simply picking a reasonable topic to pursue. In this, Cuy was a great help, and I soon understood why he had attracted such good people to the three different departments that he had organized by then, and why their research generally flourished. He was every bit the paternal adviser I had imagined and helped me to get going in all kinds of ways, many of them having nothing to do with science. After I had been plugging away for a couple of months with the equipment that he had arranged to have waiting for me in St. Louis (new and much finer than what I had been used to during the preceding two years at UCL), he came by the lab one day to ask why I had chosen not to enroll in TIAA-CREF, the academic pension fund. I told him that I really wasn’t worried about retirement at that point and that Shannon and I couldn’t afford to pay the monthly contribution. He patiently explained what an annuity was, the virtues of compound interest, and why this eventually would be important, as of course it was. More to the point, he raised my salary that very day so we could afford to make the contribution.

Working on neuronal connections in the mammalian autonomic system was, as it turned out, another good choice. Although I saw this work as a stepping stone toward a more direct attack on problems explicitly related to brain function, the step eventually consumed about a dozen years with results that, in contrast to what I had done up to that point, were regarded as important. During the first few years in St. Louis, I undertook two projects in the peripheral autonomic system of mammals. The first was directly inspired by observations John Langley had made 80 years earlier. In the course of neural development in embryonic and early postnatal life, connections between nerve cells must be made appropriately. Experience later in life is, of course, important in the ultimate organization and further refinement of connections, but the idea that the human or any other brain comes into the world as a tabula rasa is silly. Nervous systems at birth are already connected in detailed and highly specific ways based on the experience of the species over evolutionary time. The mechanisms that produce this specificity of connections during development were unclear in 1973 and to a surprising degree still are.

Langley had examined this issue at the end of the 19th century, making use of the fact that neurons at different levels of the spinal cord innervate neurons in sympathetic ganglia in a stereotyped way. In the superior cervical ganglion, for example, cells from the highest thoracic level of the spinal cord (T1) innervate ganglion cells that project in turn to smooth muscle targets, such as the muscle that dilates the pupil, whereas neurons from a somewhat lower level of the cord (T4) innervate ganglion cells that cause effects in other targets, such as constricting the blood vessels of the ear. Langley had assessed these differences in the innervation of the ganglion simply by looking at these peripheral effects while electrically stimulating the outflow to the ganglion from different spinal levels in anesthetized cats, dogs, and rabbits. When he stimulated the outflow from the upper segments of the thoracic spinal cord, the animals’ pupil dilated on the stimulated side without any effect on the blood vessels of the ear, whereas when he stimulated the lower thoracic cord segments, the pupil was not affected but the blood vessels in the ear on that side constricted. Moreover, when he cut the sympathetic trunk that carried the axons to the ganglion and waited some weeks for them to grow back, he observed the same pattern of peripheral responses. Langley thus surmised that the mechanisms underlying the differential innervation of the ganglion cells must occur at the level of synapse formation on the neurons in the ganglion. He further suggested that selective synapse formation is based on differential affinities of the pre- and postsynaptic elements arising from some sort of biochemical markers on their respective surfaces.

Given these studies and more modern ones by Roger Sperry at Caltech, it seemed well worthwhile to pursue the issue of neural specificity at the level of electrical recordings from individual neurons in autonomic ganglia. Arild Njå, a postdoctoral fellow from Oslo, who was the first to come my way, and I pursued the merits of this idea in the autonomic system of guinea pigs by dissecting out the whole upper portion of the sympathetic chain, keeping it alive in a chamber, and making intracellular recordings from individual neurons in the superior cervical ganglion while stimulating each of the input levels from the spinal cord. The results showed that the synaptic connections made on ganglion cells by preganglionic neurons of a particular spinal level are indeed preferred, but that contacts from neurons at other levels are not excluded. Furthermore, if the innervation to the superior cervical ganglion was surgically interrupted, recordings made some weeks later indicated that the new connections again established a pattern of segmental preferences. Thus, neurons of the spinal cord associate with target neurons in the autonomic ganglia of mammals according to a continuously variable system of preferences during synapse formation that guide the pattern of innervation during development or reinnervation without limiting it in any absolute way.

Although this work with Arild resulted in several good papers, it was another project I had begun in parallel that eventually occupied most of my attention over the next decade. The ideas on which this work was based came from another direction altogether. The theme that Bert and I had been working on in London was control of the signaling properties of neurons (although we used muscle cells as a model), and I continued to think—along with many others—that such modulation of signaling and its effects on connectivity over the long haul was especially important. In the first couple of papers to come out of my lab in St. Louis, I showed by electrophysiological recording that the efficacy of the synapses made by the spinal neurons on the neurons in the superior cervical ganglion declined over the first few days after the axons from the neurons to peripheral targets in the head and neck had been cut, and that this decline occurred in parallel with the loss of a majority of the synapses made on the ganglion cells that could be counted in the electron microscope. Because the loss of synapses from the neurons was reversed when the axons grew back to their peripheral targets, the conclusion seemed clear: the synaptic endings made on nerve cells do not just sit there but have to be actively maintained. And whatever the mechanism, this maintenance depended on the normal connections between nerve cells and the targets that they innervated. The clarity of these results in a relatively simple system of mammalian neurons was news, and it encouraged further studies along these lines.

This research led to the beginning of a long collaboration with Jeff Lichtman and a deepening friendship with Viktor Hamburger, both critical determinants of how this work progressed. Jeff appeared in my lab one day in 1974 and asked if he could chat about his future. He was then a second-year med student and knew me from the lectures on neural signaling I had given to his class some months before. Jeff was in the MD/PhD program, and he was trying to figure out what to do for his doctoral work. He seemed nervous and lacked a good reason for wanting to work with me or ideas about what to do. I think he simply saw me as someone who was young and ambitious and who, based on the lectures he had heard, might be a good mentor. My inclination was not to take him on since my experience at Harvard and UCL had been that the best people populated their labs with postdoctoral fellows rather than graduate students. But before reaching a decision, I thought it would be a good idea to ask Cuy. He pointed out that the MD/PhD students were a highly select group, that Jeff would not cost me anything since the program was fully funded by the National Institutes of Health, and that unless I had a very good reason not to I should certainly take him on. Cuy was indeed right: Jeff was—and remains—one of the smartest and most imaginative people I have known in neuroscience and went on to become a major figure in his own right.

Getting to know Viktor Hamburger was equally important. Hamburger was far and away the most notable neuroscientist at Washington University in 1973. Because he was in the Biology Department on the undergraduate campus, I had not met him on my trip to St. Louis as a faculty candidate, and to my great embarrassment, I knew little or nothing about him or his work when I arrived in St. Louis. This woeful ignorance brought home to me the parochial nature of my training up to that point. Viktor was a consummate biologist and my conversations with him about his work and neural development led me to think more and more about what nervous systems do for animals and less about the details of neurons.

As I gained some familiarity with Hamburger’s work, it dawned on me that his expertise was especially relevant to what I was doing in the autonomic system, or at least to the part that involved looking at the failure of synaptic maintenance when neurons were cut off from their peripheral targets. Viktor had used the embryonic transplantation techniques learned from Hans Spemann to either add or take away limb buds in embryonic chicks, assessing what happened to the spinal neurons that would have innervated the ablated limbs, or that innervated the extra peripheral targets. The upshot of this work begun in the 1930s was to establish the phenomenon of target-dependent neuronal death or survival. By the 1970s, neuronal death regulated in this way during development had been shown to be a general phenomenon in the peripheral nervous system and in some parts of the central nervous system. A corollary was that the developing neurons in the spinal cord were competing for acquisition of the postulated agent, dying off if they didn’t get enough of this “trophic” stuff. This work on the regulation of neuronal numbers in early development by trophic interactions had been greatly advanced by a collaboration that Hamburger began with Rita Levi-Montalcini in the late 1940s. Their work together lasted for about eight years and led to the discovery of nerve growth factor, a trophic molecule derived from smooth muscle that is the “nourishing” agent for at least two types of neurons, one of which was the nerve cell type in the ganglia of the sympathetic nervous system I had been working on. Nerve growth factor has served as a paradigm for the interactions between nerve cells and their targets ever since and remains the best example of trophic interactions in neurobiology.

What I learned from Viktor in the 1970s about neural development and nerve growth factor had a significant impact on what was going on in my lab, where by now several people were toiling away on the formation and maintenance of synaptic connections in the simple and accessible systems that various autonomic ganglia in mammals provided. Like Hamburger, I had never had much interest in studies at the molecular level; among other reasons, my brief but dismal experience with neuropharmacology research as a med student left a lingering bad taste and most molecular studies seemed to me then (and still do) to be learning more and more about less and less. The nerve growth factor, however, was an exception. This agent not only promoted the survival of the very neurons we were studying but also influenced the growth of the axonal and dendritic processes of the classes of neurons that were sensitive to it, and by implication the synaptic contacts they made. It was not hard to imagine that competition for and acquisition of such factors was the basis of the maintenance of synaptic connections we had been providing evidence for and that this “trophic theory” of how synapses were regulated in the nervous system could well be a general rule.

The idea was that each class of cells in a neural pathway was supporting and regulating the connections it received by trophic interactions with the cells it innervated down the line, resulting in a coordinated chain of connectivity that extended from the periphery centrally to the spinal cord and ultimately on through the controlling centers in the brain. The aim in this work on synaptic connectivity in mammals was not to sort out which molecules might be involved (the paradigm provided by nerve growth factor was sufficient evidence on that score and by the mid-1970s many labs were studying this agent), but rather the governing principles of neuronal competition. In pursuing that goal, Jeff Lichtman was the prime mover. The main problems that concerned us for the next several years were the nature of competition among the axons that innervate target nerve cells and how the signaling activity of competing nerve cells affects the balance of synaptic connectivity. The theme was the conviction that nerve cells and their targets must interact in sorting out the connectivity of functioning circuits in much the same way that elements in an ecosystem eventually establish an equilibrium as they compete for limited resources.

The closest anyone had come to directly exploring the issue of synaptic competition by the mid-1970s was a study of the developing innervation of skeletal muscle fibers carried out by Michael Brown, David Van Essen, and Jan Jansen. I didn’t know Brown, but Van Essen had been a graduate student at Harvard when I was there (he joined the Nicholls lab for his doctoral work about the time I left to work with Jack McMahan), and Jansen had worked in the Nicholls lab when on sabbatical from his position in Oslo that same year. Back in Oslo a few years later, they had shown that during the first few weeks of postnatal life, each fiber in a rat muscle is contacted by more nerve terminals from different axons than persist in maturity, providing another clue about the nature of synaptic competition and maintenance. A natural question was whether the innervation of neurons followed the same rules as muscle fibers, and Jeff’s thesis showed that it did.

Although understanding the interactions among axon terminals and the synapses they make on target cells remains incomplete, some important principles emerged from the work carried out by Jeff and several other fellows in the lab over the next few years. One is that the spatial configuration of a neuron is a critical determinant of the innervation it receives. For nerve cells without dendritic processes, the end result of the initial competition is innervation by many synaptic endings, all arising from the same nerve cell axon. If a target nerve cell has dendrites, however, the number of innervating axons increases in proportion to the number and complexity of its branches. Moreover, once a given axon makes some synapses on a target neuron, the axon is informed by the conjoint activity of the pre- and postsynaptic neurons that the target cell is a favored site for the elaboration of additional synaptic endings. This focusing of synapses occurs despite the presence of numerous other valid target neurons in the immediate vicinity. Thus, the synaptic terminals made on a target neuron act as sets rather than as individual entities during the establishment of neural circuits. This and much other evidence implies that neural activity—action potentials that release transmitter at the synapses in question—is importantly involved in circuit formation.

Intriguing though these observations were, it was increasingly clear that to understand what was going on during the formation and maintenance of synapses, one would have to figure out a way to directly monitor the progress of synaptic contacts on the same target cell over periods of days, weeks, months, or longer. This goal seemed technically feasible in the peripheral nervous system and would allow us to watch how competition operated during development and how synaptic connections went on being modified in maturity. Since encoding experience during life depends on functional and anatomical changes in neural connectivity, the expectation was that synaptic connections would change gradually over time and that we would be able to witness the process in action. A next step was therefore to figure out how to observe the same synapses chronically.

Our first stab at this goal was based on the ability to identify the same neuron in the autonomic ganglia of a living animal on different occasions. Given that each neuronal cell body has a somewhat different appearance in the cobblestone-like pattern of cells visible on the surface of a ganglion, it is not hard to find the same neuron during an initial surgical exposure and at a second such operation after an arbitrarily long interval. An identified neuron thus could be injected with a non-toxic dye and the configuration of its dendrites photographed. By carrying out the same procedure weeks or months later, we could ask how dendritic branches changed over time. Since the dendrites of ganglion neurons are studded with synapses, any change in the architecture of the dendritic branches would imply ongoing changes in synaptic connectivity. It was evident from these initial studies that dendrites are continuously remodeled, and therefore that the synaptic connectivity of the neurons must be changing as well.

Monitoring the synaptic endings themselves over time would of course be more revealing, and this is what we set out to do next. The problem in this project was that, unlike the cell bodies, synapses are far too small to be directly injected with a dye. To visualize synapses, we needed a dye that the terminals would take up quickly and would then diffuse away without damaging the endings. Finding such a reagent was a matter of trial and error, and the person who undertook this thankless task was Lorenzo Magrassi, a smart, hard-working medical student from Italy who had come to spend a year in the lab in 1985. Lorenzo, who knew quite a lot of chemistry, applied one plausible reagent after another to synaptic endings on mouse muscles in a dish while he observed the results. When after many weeks of this he finally succeeded in finding a dye that met these criteria, Jeff Lichtman (who was by then a faculty member at Wash U), Lorenzo, and I began monitoring synapses on muscle fibers over months by finding and re-staining the same synaptic endings. The method also worked for the synaptic endings on identified ganglion cells, and synapses on neurons could be followed over time in the same way. In both cases, synaptic terminals gradually changed, slowly on mature muscle fibers and faster on neurons.

Although this effort to understand the formation and maintenance of synapses had been successful by the mid-1980s, things as I saw them were not going so well. The reasons were several and had only partly to do with science. With respect to the science, it was not clear at that point what to do next. Directly monitoring synaptic change in muscle fibers and ganglia had been a fine start. But no one was going to get very excited with this work if it could not be extended to synaptic stability in the brain. It was the brain, after all, that determined behavior and the cognitive processes I and everyone else wanted to understand. I had viewed these studies of synapses in ganglia and muscle as simple systems for getting at what was likely to be happening in more interesting parts of the nervous system. But the techniques we had been using were difficult enough to apply in the peripheral nervous system, and for various reasons, were hard to imagine applying to synapses in the brain. Within a decade, further advances in molecular biological methods resolved this impasse by providing labels that could be introduced into neurons by gene transfection. This methodology eventually allowed Jeff and his collaborators and others to begin to tackle these sorts of problems in the brain. But that possibility was not on the horizon in 1985.

Other factors were also at work. Cuy Hunt had retired and moved to France. As a result, I (along with Jeff Lichtman and Josh Sanes) had moved to the Department of Anatomy and Neurobiology in 1986. Gerry Fischbach was running the department as Max Cowan had left to take a position as the chief scientific administrator at the Howard Hughes Medical Institute. Gerry was a fine chair. But he was a peer, creating a situation quite different from the paternal figure Cuy had been. Finally, there was an increasing awkwardness between Jeff Lichtman and me. Jeff by then had his own successful lab and, although we had continued to collaborate, the relationship was no longer the one I had enjoyed for many years. We were now working on similar issues and, to some degree, had become competitors.

In a couple of years I would be 50, and the undeniable fact of middle age combined with these several circumstances triggered another bout of depression, this one more serious than those I had experienced before. Although I kept experimenting, writing papers and books (Principles of Neural Development; Body and Brain) and carrying out teaching assignments, my usual enthusiasm had begun to wane. I saw a psychiatrist who started me on an antidepressant, and when the drug he prescribed didn’t work, my depression deepened. Mainly as a result of my wife’s support, the counsel of another psychiatrist, a different medication, and perhaps just the passage of time, I gradually began to see a plausible future again.

Having returned to a better frame of mind, I felt I had achieved enough success to take some bigger scientific chances. I had started out with broad philosophical interests in the brain, but by virtue of my training, the people and the science that I admired, and the overall direction of neuroscience, I was still de facto a reductionist. With perhaps another 20 or 25 years or so to go, I felt I owed it to myself to at least think about doing something that might go beyond the conventional framework that I had assiduously learned, worked within, and taught for what by then was two decades.

Tackling the Brain

If I was going to pursue research on some aspect of the brain, it was clear I would need a remediation and the first order of business was to find a good teacher. In this regard, I was especially lucky in 1987 when Anthony LaMantia, who had just finished his doctorate with Pasko Rakic at Yale, got in touch with me about joining the lab as a postdoctoral fellow. Rakic was the most accomplished and imaginative neuroanatomist in the country, and I had followed his work on the development of the primate brain closely. His knowledge and talent rubbed off on his trainees, and given my new inclination, Anthony’s arrival in the lab the following year was a godsend. I learned far more from him over the next few years than he from me.

Relearning brain anatomy, however, was only preliminary to figuring out a good problem to explore. Typically, investigators extend their research in directions with which they are familiar, making an educated guess about what an interesting tangent might be. This is what Anthony and I did, ultimately deciding to tackle neuronal development and stability in the olfactory system. By 1988, the work on monitoring synapses over time in the peripheral nervous system was winding down for me. Anthony and I would like to have monitored synapses in some region of the living brain, but there seemed no way to do that. We therefore settled on what we thought was the next best thing: monitoring the development and maintenance of brain “modules.”

The modular units we chose to look at first were the glomeruli in the olfactory bulb of the mouse. The reason for the choice was not that these were the most interesting cortical patterns—that prize went to ocular dominance columns in the visual cortex. Glomeruli, however, were practical modules to begin with. Mice were cheap and we would have to use lots of animals to work out methods for exposing the brain, staining these units with a nontoxic dye, and repeating the procedure to examine the same region weeks later. We succeeded over the next year or so showing that new units were added among the preexisting ones as the mouse brain developed. These findings about the olfactory system were not, however, news that anyone had been waiting for. The focus of interest cortical modularity and the visual system and it was the brain region that had stimulated the most ardent debates about the role of modularity.

As a student in Rakic’s lab, Anthony had had plenty of experience working with rhesus monkeys, and so we turned next to the monkey visual cortex. For a variety of reasons, it was impractical to carry out repeated monitoring in the same monkey as we had done in the mouse. We again settled for the next best thing. Given what we had found in the mouse olfactory bulb, it seemed reasonable to look at the overall number of modular units in the visual cortex shortly after birth and in maturity in different monkeys. If the numbers were significantly different, it would follow that units had been added as monkeys matured, much as we had documented in the olfactory brain of the same mouse. The easiest units to look at in the monkey visual cortex were the so-called “blobs.” These visual system modules had not attracted the same attention as ocular dominance columns, but they were discrete and could be easily counted.

The project, however, was problematic from the outset. Although I had worked on lots of different species over the years, including small monkeys, adult rhesus monkeys are large and often nasty. The expense, the character of the animals, and the knowledge that the project would be only a stepping stone to a more direct approach made us hurry along and eventually publish a wrong conclusion. On the basis of the first few animals in which we counted blobs at birth and in maturity, it seemed reasonably clear that these units were being added. Anxious to stake this claim in the monkey visual system and convinced that the results we had seen in the mouse olfactory bulb indicated a general rule, we went ahead and published a short paper to that effect. When we completed the study with a larger complement of monkeys, however, we found no significant difference in the initial and mature number of blobs in the visual cortex. We corrected our mistake in the full report of the project and no one seemed to have paid much attention to our error, but I realized that I had pushed too hard in the interests of being recognized as a player in the community of “brain scientists.” This minor fiasco left me considerably less confident about making the transition from the peripheral nervous system to the brain. It also left me with the need to come up with another research direction, as there seemed no great merit in pursuing the long-term stability of modular units in the visual cortex (to judge from our work on blobs and other evidence we should have paid more attention to, they are pretty stable over primate development).

Duke

While all this was going on, our lives were changing in another way. In 1990, I accepted an offer from Duke University to start a Department of Neurobiology, and Shannon and I and our younger daughter had moved to North Carolina (which is where Anthony and I carried out the work on monkey blobs). Duke had raised the sum required to hire and set up about a dozen new faculty and had put up a new building to house the department. This largesse coupled with the quality of the university and its ambitions presented an opportunity that was hard to turn down, even though it promised some administrative work that I had always shunned.

The move turned out to be significant in many ways, almost all of them positive. My less than robust mental state when I accepted the job at Duke benefited greatly from the change of scene and the challenge of starting a new department. I had been at Washington University 17 years, and my crankiness at the end of that time, the problematic relationship with Jeff Lichtman, and my desire for a new scientific start were all more or less resolved in one fell swoop. The move was also a big plus for Shannon. Shannon (known as Shannon Ravenel in the publishing world) had been a successful young fiction editor with Houghton Mifflin in Boston when we married in 1968, but had given up her job when we moved to London in 1971. During our first few years in St. Louis, she had taken on a series of minor editorial jobs to make ends meet that were as demeaning to her as it would have been for me to teach high school health science at that point in my career. Her professional situation improved in 1977 when Houghton Mifflin asked her to become the series editor of their annual anthology “Best American Short Stories,” a job she could do in St. Louis that entailed selecting stories published each year in North American periodicals. Shannon’s situation improved again in 1982 when her friend and mentor, Louis Rubin, asked her if she would be interested in starting a literary publishing company in Chapel Hill, where he was professor of English at the University of North Carolina. She agreed, and had been exercising her role in this new venture from St. Louis. But as Algonquin Books of Chapel Hill grew increasingly successful, this arrangement had become awkward. As Duke is only 10 miles from Chapel Hill our move solved problems for both of us (Algonquin Books was bought by Workman Publishing Co. in New York in 1989, and continues to flourish).

The first of several new postdoctoral fellows to join my lab at Duke was David Riddle, a PhD from the University of Michigan, and the direction that seemed most attractive involved yet another region of the mouse brain that had long been of interest: the somatic sensory system. Although not as thoroughly plowed as the visual system (and for many people, intrinsically less interesting), the somatic sensory system had some advantages. The major attraction was that the cortical representation of the body surface can be seen and measured.

David and I (and eventually another fellow, Gabriel Gutierrez) wanted to see whether the regions of sensory cortex that experienced more neural activity during maturation captured more cortical area than less active brain regions. We could explore this question by measuring the area occupied by different components of the somatic sensory map at different ages, asking whether the more active areas grew faster. If this correlation could be established, the implication would be that the neural activity generated by an animal’s experience in life was being translated into the allocation of more cortical area to process the relevant information (i.e., a manifestation of the influence of neural activity on cortical connectivity). This turned out to be the case: the more active cortical regions expanded relatively more during maturation than less active ones.

Taking stock, by the early 1990s, I had put in about five years working on these various projects in the brain at Duke and felt more or less knowledgeable about the issues with a reasonable grasp of brain anatomy. To show my willingness to participate in the grunt work of the new department, I was teaching Duke med students each spring; although I was certainly no expert, I no longer embarrassed myself when answering questions about neuroanatomy. Although work on the growth and organization of the cortex as a function of activity continued, as much from scientific boredom as from any clear goal, I began thinking about vision more broadly, fiddling around with some small projects on perception that seemed interesting but minor asides to the mainstream neuroscience that was plodding along in the lab.

Visual Perception

Perception—that is, what we see, hear, feel, smell or taste—is generally thought of as the end-product of sensory processing, eventually leading to appropriate motor or other behavior. But if one thinks about it, perception is far more complicated than this garden-variety interpretation. Why is it that what we see or otherwise experience through the senses fails to tally with corresponding physical measurements? And what do these discrepancies have to do with the longstanding philosophical inquiry into the question how can we know the world through our senses in the first place? Once I had begun to work on sensory systems, these and other questions about perception kept intruding and were harder and harder to ignore. They are, after all, pretty basic.

Like most mainstream neuroscientists, however, I was leery of devoting much time to questions that generally are looked down on as belonging to psychology or, worse yet, philosophy. I had first gotten a sense of this bias as a postdoc in the Nicholls lab circa 1970, when we had lunch everyday with the Hubel and Wiesel lab. Because they were working on vision, Hubel and Wiesel were familiar with many of the controversies and issues in visual perception. But the only psychologists I remember them taking seriously were people like Leo Hurvich and Dorothea Jameson who devoted their careers to painstaking psychophysical documentation of lightness and color percepts and models of how these phenomena might be explained. When less rigorous psychologists came up in conversation, Hubel would refer to them as “chuckleheads,” a term he used quite a lot (and did not limit to psychologists). Likewise, the rest of my mentors and colleagues at Harvard, University College London, and later Washington University didn’t waste much thought on psychology or its practitioners; by and large, this sort of work was deemed irrelevant to the rapid progress of the reductionist neuroscience that nearly all of us were doing. Psychology as science was considered not up to par, and philosophical questions were simply nonstarters.

In 1994, I undertook the first of several mini-projects on perceptual issues with another postdoc, Len White, that we both regarded simply as interesting diversions from the tedious project we had embarked on. Len was a superbly trained neuroanatomist who had recently gotten his doctorate with Joel Price, one of Max Cowan’s original hires at Washington University. We had been looking at the neural basis of right- and left-handedness by laboriously measuring the cortical hand region in the two hemispheres of human brains. Based on the effect of activity on the allocation of brain space in rodents, we thought that human right-handers would very likely have more cortex devoted to that hand in the left hemisphere where the right hand is represented. Thus, Len and I were in the process of measuring this region in hundreds of sections of human brains removed at autopsy.

People are not just right- or left-handed, but are also right- or left-footed, and, interestingly, right- or left-eyed. To leaven the load of measuring the right- and left-hand regions in what ended up being more than 60 human brains, we started thinking about right- and left-eyed-ness. The question about perception we asked was whether people who were either right-eyed or left-eyed when sighting with one eye (e.g., aiming a rifle) expressed this preference routinely when viewing the world with both eyes. To this end, we covered a large panoramic window with black paper into which we had cut about a hundred holes the diameter of a tennis ball. We asked subjects to simply wander around the room and look at the scene outside though one or another of the holes, which they would necessarily have to do using one eye or the other. This setup mimicked the everyday situation in which we look at the objects in a scene that lie beyond occluding frames in the foreground. As subjects looked at the outside world through the holes from a meter or two away, we monitored whether they used the right or left eye to do so, and whether the eye they used agreed with the eyed-ness they showed in a standard monocular sighting task. It did, although as far as I know, no one paid the least attention to the short paper that we published on this. Doing this work, however, and thinking about the issues involved, was a good deal more fun than measuring the hand region in human brains (which, as it turned out, showed no significant difference between the cortical space devoted to the right and left hand in humans). It also raised eyebrows among my colleagues in the Department of Neurobiology. When they walked by and saw the papered-over window with people wandering around looking out through little holes, it was apparent that some weird things were going on in my lab. The young faculty I had begun recruiting to the new department seemed mildly bewildered at the apparent flakiness of what we were doing, which was very far from neurobiology as they understood it.

A different project in perception we undertook at about the same time was just as peculiar but less trivial and accelerated my transition toward a focus on perception as such. Another postdoc, Tim Andrews, had gotten his degree in the United Kingdom working on trophic interactions and had come to Duke expecting to work with me on some related issue. But when he arrived, the attraction of perception caught him up as well, and he became the first postdoc to work primarily on perception. The eyed-ness project uncovered a lot of interesting literature, including several papers by Charles Sherrington describing little-known experiments on vision that carried out in the early 1900s. In Sherrington’s highly influential work on motor reflexes, one of his principal findings was that actions were routed through a “final common pathway.” By this, he meant that the output of all the neural processing that goes on in the motor regions of the brain ultimately converges onto the spinal motor neurons that innervate skeletal muscles, which in turn generate motor behavior. It thus was natural for him to ask whether the same principle might apply to perception.

Sherrington recognized that the sensory nervous system provided a good venue in which to address this question, namely, the processing carried out by the neurons in the visual system that are related to one eye or the other. If the information from the two eyes is brought together in a “final common pathway” in the visual brain, then the combined asynchronous left- and right-eye stimulation should be perceived as continuous light at roughly half the normal flicker-fusion frequency. The result Sherrington obtained, however, was that the on-off rate at which a flashing light becomes steady is identical in the two circumstances. On the basis of this observation—which Tim Andrews and I confirmed—Sherrington concluded that the two retinal images must be united “psychically” rather than physiologically, thus lying beyond his ability (or interest) to pursue.

For better or worse, Tim and I and other students and fellows in the lab continued down this path over the next couple of years, carrying out a series of projects on visual perception that examined other odd phenomena, such as the wagon-wheel illusion in continuous light, the rate of disappearance of the images generated by retinal blood vessels, the strange way we perceive a rotating wire-frame cube, and the rivalry between percepts that occurs when one stares long enough at a pattern of vertical and horizontal stripes. All the while, the lab was carrying on conventional projects on handedness, the way cortical organization was affected by the prevalence of differently oriented contours in natural scenes and other unfinished business in mainstream neurobiology. The reality, however, was an ever-greater interest in perception, and less and less devotion to mining issues of brain structure and function with the sorts of electrophysiological and anatomical tools I was familiar with. In the end it led to far more important work than I had done earlier.

The tipping point came in 1996. By then I was in my late 50s, and after seven or eight years puttering around with how activity affects brain organization, I still hadn’t stumbled across anything that was deeply exciting. With perhaps 10 or 15 good working years left, I began to think that I should spend all my remaining time working on perception. I had learned enough about the brain and the visual system to have a sense that the attempt to explain perception in terms of a logical hierarchy of neuronal processing in which properties of visual neurons at one stage determine those at the next was wrong in some fundamental way. No percept had been convincingly explained in these terms and a wealth of visual perceptual phenomena remained unclear. In science, when that much time goes by without success, it usually means that a field is on the wrong track.

I was pretty sure that given my age, the raised eyebrows of my colleagues, and my lack of serious credentials in vision science, it would be an uphill fight to support a lab focused explicitly on perception (up to that point, I had been using money from grants for the ongoing conventional work in the lab to support our perceptual forays). I also sensed that I was coming to be seen as something of an oddball and was less-often invited to high-profile meetings or to lecture at other institutions. Conversely, work on perception doesn’t cost much to do, and I knew that if I didn’t take the plunge at that point, I would not have a second chance. And so I plunged.

Lightness and Color

The observation in 1997 that set me thinking in earnest about a possible answer to the challenge of perception was a picture. I don’t remember the subject, but in the course of a noontime seminar, the speaker showed a popular visual illusion. It was not that the information in a scene influenced perception of some particular part of it—Michel Chevreul, Hermann Helmholtz, the Gestalt psychologists and pretty much everyone else had recognized that. What struck me was that an accumulation of this information arising from trial-and-error behavior in response to retinal stimuli provided a way of getting around the problem presented by the inability of biological vision to measure the physical world. Looking at perception in this way also suggested why the standard ideas about what visual neurons were doing had come a cropper, and perhaps a way of understanding what the connectivity of visual neurons was actually accomplishing. I was excited enough about the idea that perceptions might be determined in this way to go back to the lab after the lecture and seek out Mark Williams, a postdoc who was especially skilled in computer graphics (a methodology that was far more challenging then than it is with today’s user-friendly software). I sketched a crude scene and tried to explain what I thought might be going on. Although what I said couldn’t have made much sense, it was enough to get Mark interested. Within a few weeks, he created a series of computer programs that we used to test the idea that the lightness values people see are determined by linking accumulated experience with patterns of luminance to perceptions (and other behaviors) that would have been helpful in response to the stimulus in question.

Perceptions of lightness seemed a good place to start. Of the basic qualities that define visual perception (lightness, brightness, color, geometric form, distance, depth, and motion) the most important is seeing relative light and dark. Because it would presumably behoove us to see the world as it “really is,” a logical expectation is that lightness derives from the luminance of a stimulus: the more light falling on some region of the retina, the lighter that target should appear. But this expectation is not met; indeed, we never see the world as a photometer measures it. A simple example is that two central patches with the same luminance are perceived differently depending on the luminance of the surround (a phenomenon called “simultaneous lightness contrast”). Over the next year, Mark and I and a bright premed student (Alli McCoy) put together enough evidence to write a couple of papers on how subjects perceived the lightness of test patches in scenes with different empirical meanings. The implication was that the different lightness values we see are determined by accumulated experience with luminance patterns in retinal images.

The problem that we took to underlie these effects is that biological visual systems lack the tools needed to measure real-world parameters. If the lightness values we see were simply proportional to luminance, the result would be a useless guide to behavior. If, however, our sense of lightness is generated empirically—that is, by trial-and-error accumulation of information that reflected successful behavior in response to retinal patterns—this problem could be resolved. Our idea was that the frequency of occurrence of image patterns in human experience would have determined the evolution of the relevant visual circuitry. As a result, neural connections that linked the visual stimuli to operationally useful perceptions would gradually wax in the visual brains of the population. Perceptions arising in this way would not correspond to any particular feature of the stimulus but to the perceptions that had generated successful behavior in the past.

Given this conception of vision, the next step was to test its validity in a more serious way. Pursuing this goal over the next few years depended critically on Beau Lotto, a postdoc who arrived in the lab in 1998. Like Tim Andrews, Beau had done his doctorate in developmental neurobiology in the United Kingdom and had come to my lab with the idea of pursuing some developmental issue in vision. But by the time he arrived, my interest in visual perception was fully in the ascendancy. After some initial backing and filling about what to do, Beau threw himself into the work on perception and had all the skills needed to push things along in new and imaginative ways. He grasped the nub of conceptual or technical problems right away and had the intelligence and tenacity to solve them. Furthermore, he was (and is) as much an artist as a scientist, and his ability to make visual tests and demonstrations was invaluable. Because we had no idea how to acquire or analyze data that could serve as a proxy for human visual experience with luminance, we started with the easier task of showing that some of the most perplexing lightness effects (e.g., Mach bands, the Cornsweet edge effect, and the Chubb effect) had plausible empirical explanations.

Although Beau and I were pleased with what we took to be clever empirical explanations of phenomena that had puzzled people for a long time, the general response of vision scientists was that these accounts were “just-so stories” that could not be taken seriously because they were not connected to information about the receptive fields of visual neurons that everyone assumed would eventually explain perception. This was frustrating because if we were right, the relationship between the properties of visual neurons and perception would never be explained in the logical framework that was then in play. If a wholly empirical strategy of vision is the operating principle, then the visual brain was a welter of neuronal connections built historically over evolutionary and individual time according to all the factors that determine successful behavior. Not surprisingly, people whose careers were founded on the supposition of logical computation did not welcome our ideas.

In an empirical conception of vision, making sense of the neurophysiology underlying perception ultimately would depend on understanding the evolutionary history of the human nervous system in terms of behavior. And that goal seemed impossible, at least in the short term. But if we had a proxy for human visual experience with some aspect of the natural world—say, experience with retinal luminance patterns—we could at least test whether accumulated experience predicted some of the lightness perceptions we had been concerned with. Although we began to think more about this possibility, it was not clear how to proceed in 1999. The easier path was to load on more evidence by examining the perceptions elicited by other visual qualities, asking whether further perceptual puzzles could be accounted for in this way. And the quality that seemed best suited to this purpose was color.

Seeing in color is the perceptual quality generated in many visual animals when the light energy in a stimulus is unevenly distributed, and Beau and I felt pretty sure that color perceptions could also be explainable in empirical terms. Thus, we set about exploring whether the way we see color is the result of accumulated trial-and-error experience with spectral relationships.

We first tested this idea by having subjects adjust the perceived color of a target on a neutral background until it matched an identical target on a colored background, thus measuring the perceptual change induced by the color of the surround. The upshot was that we could enhance or diminish color contrast effects by making the characteristics of a scene either more or less consistent with different sources of the light spectra coming from target patches. For example, when identical targets are presented on backgrounds that include a variety of tiles with spectra designed such that the two arrays are likely to be under “red” and “blue” illumination, the apparent color difference between the targets is relatively marked. Conversely, when the contextual information is consistent with the arrays being under the same illumination, the apparent color difference of the physically identical targets decreased. Because the average spectral content in scenes was the same, these effects could not be explained by adaptation or neuronal interactions at the input stages of the visual system. In empirical terms, however, the color perceptions elicited by the same targets in different contexts—i.e., contrast and constancy—made sense.

Although Beau and I were sold by the outcome of these studies, the response from the vision scientists who we thought might be converted was a collective yawn. The papers we wrote invariably were given a hard time by anonymous reviewers; granting agencies were unenthused; and even local colleagues showed only polite curiosity about what we were doing. Visual physiologists were unimpressed because we said nothing about how any of this could be related to the properties of visual neurons. Psychologists were equally unenthusiastic pointing out that we failed to rebut (or often even mention) other explanations. Although there was certainly some truth in this complaint, the main objection seemed to be that in coming at these issues from a different tradition, we lacked the necessary credentials to intrude in this arena and failed to appreciate the conventional wisdom.

Analyzing Spectral Databases

A way to determine the accumulated experience we took to underlie these lightness and color phenomena was to examine spectral relationships in databases of natural scenes. The way to do this was devised by two postdoctoral fellows who recently had come to the lab from China, Fuhui Long and Zhiyong Yang. Fuhui was a quiet young woman whose retiring demeanor concealed a vivid intelligence and a determination I had rarely encountered. Fuhui had received a doctorate in computer science and electrical engineering and had been a postdoc in the Department of Electronic and Information Engineering at Hong Kong Polytechnic University, where she had worked on image processing and computer vision. As a result, she was familiar with a wide range of technical approaches to image analysis; her purpose in coming to my lab was to gain some knowledge about the biological side of things.

Fuhui collected about a thousand high-quality digital photographs of representative natural scenes and wrote the programs needed to extract the physical characteristics associated with hue, saturation, and color brightness at each point in millions of smaller samples taken from these images. Our assumption was that this database would fairly represent the spectral relationships that humans had always experienced and thus allow us to predict the classical colorimetry functions. If the organization of the perceptual color space has been determined this way, then the effects of routinely experienced spectral information should be evident in the ability of subjects to discriminate color differences as the wavelength of a stimulus is varied. The relevant psychophysical functions could then be compared with the functions predicted by analyzing the spectral characteristics of millions of samples from natural scenes. Although certainly not perfect, there was good agreement between the psychophysically determined functions and the functions we predicted from the empirical data.

Just as important was to go back and show that the perception of lightness could be explained by the frequency of occurrence of luminance patterns, and Zhiyong Yang set about this task. He had received a doctorate in computer vision from the Chinese Academy of Sciences, and before coming to the lab, he had done postdoctoral work with David Mumford at Brown working on pattern theory and with Richard Zemel at the University of Arizona working on probabilistic models of vision. Like Fuhui, his skills were well suited to extracting empirical information from scenes to figure out how this information could explain the otherwise puzzling way we see lightness. Much like accounting for colorimetry functions, the idea was that human experience with the patterns of light intensities in achromatic retinal images would account for lights and darks that we actually see. This universal experience would have led to visual circuitry that determined perceived lightness values of the elements in a given pattern according to their relative rank of in all achromatic patterns witnessed over individual and evolutioary time. Using this general approach, Zhiyong showed that the frequency of occurrence of luminance relationships extracted from natural scenes with templates configured in the form of other stimuli predicted a variety of complex lightness percepts.

Geometry

If vision operates empirically, then the same scheme should also explain the way we see spatial intervals, angles, shapes, and distances. It was not clear to anyone in the lab, however, how to pursue this. The answer appeared in the person of Catherine Qing Howe, another superb product of the Chinese educational system. At age 10, Qing had been chosen by the Chinese Academy of Sciences as one of 30 intellectually gifted children to receive an individualized curriculum in the Beijing Middle School system. She entered Peking Union Medical College at age 15, the youngest student they had ever taken. There she became increasingly interested in cognition and behavior and determined to pursue these topics in the context of psychiatry. Her idea (much as mine had been as a first-year medical student with similar intentions) was that the best way to understand these issues was through pharmacology. During her last year in med school she was elected to represent her class in an exchange program with the University of California San Francisco Medical School. The experience convinced her to emigrate to the United States, and after receiving her medical degree in 1997, she matriculated in the neurobiology graduate program at Duke and, after a false start in molecular biology, ended up in my lab.

Qing recognized that if we were going to explain geometrical percepts in empirical terms, she would have to determine the frequency of occurrence of geometrical images projected onto the retina, much as we had been assessing the frequency of luminance and spectral distributions in images. Accordingly, she used a laser range finder to determine the frequency of the occurrence of retinal images generated by real-world geometry. To understand this approach, consider the perceived length of a line compared with its actual length in the retinal image. In human experience, the length of a line on the retina will have been generated by lines associated with objects that have many different physical lengths, at different distances from the observer and in different orientations. As a result, it would be of no use to perceive the length of the line in the retinal image as such. In a wholly empirical concept of vision, the length seen would be determined by the frequency of occurrence of any particular length in the retinal image relative to all the projected lengths experienced by human observers in the same orientation.

Qing first asked how the perceived length of a line changes as its orientation is varied. As psychologists had repeatedly shown, the same line looks longer when presented vertically than horizontally. Oddly, however, the maximum length is seen when the stimulus line is oriented about 25 degrees from vertical. In the empirical framework, the apparent length elicited by a line of any given projected length on the retina should be predicted by the rank of the line on an empirical scale determined by its frequency of occurrence. Qing tested this explanation by assessing the projections generated by the laser-scanned scenes. By extracting all the projected straight lines from the database that corresponded to geometrical straight lines on surfaces in the three-dimensional (3-D) world, she compiled the frequency of occurrence of projected lines at different orientations. In effect, this analysis represents human experience with lines of different lengths and orientations in retinal images. When Qing used the laser-scanned data to predict how the same line at different orientations should be seen on the basis of their empirical rank, the predicted percepts matched the function that describes the lengths people actually see.

Qing and Shuro Nundy (another student involved in much of this work) took on another challenge: rationalizing the perception of angles. Like the apparent length of lines, an intuitive expectation about the perception of angles is that this basic feature of geometry should scale directly with the size of the angle measured with a protractor. This is not, however, what people see. It has long been known that observers tend to overestimate the magnitude of acute angles and underestimate obtuse ones by a few degrees. The frequency of occurrence of angle projections generated by the geometry of the world also could be determined from laser range images. The supposition was that this information would determine the odd way we see angles, which it did.

Motion

The last of the basic visual qualities we explored was how the brain perceives motion. One of the things that puzzled scientists thinking about motion is the obvious way that motion perception is affected by context. Depending on the circumstances, the same speed and direction projected on the retina can elicit very different percepts. Although such phenomena were often treated as special cases or simply ignored, if what we had been saying about vision was true, then the perception of motion should have the same empirical explanation as perceptions of lightness, color, and form. For obvious reasons, observers must respond correctly to the real-world speeds and directions of objects, and these responses are certainly initiated by the speeds and directions of objects that determine stimulus sequences projected onto the retina. But when objects in 3-D space project onto a two-dimensional (2-D) surface, speed and direction are conflated in the resulting images. As a result, the sequence of positions in 3-D space that define motion in physical terms is always ambiguous in the sequence of retinal positions generated by moving objects. If contending with this problem depended on the empirical framework that we had used to rationalize other visual qualities, then the perceptions of motion elicited by image sequences should be predicted by the frequency of occurrence of the retinal image sequences humans had experienced.

Testing this idea, however, was not so easy. There was no technical way to collect the information that we needed about the direction, speed, and 3-D position of moving objects. We could, however, approximate human experience with object motion in a virtual world in which moving objects were projected onto an image plane (a stand-in for the retina). This simulated approximation of motion experience could then be used to predict the perceived speeds and directions seen in response to motion stimuli, thereby testing the idea that motion perception is also generated empirically.

Specific examples people had struggled to explain are the flash-lag effect, which concerns the perception of speed, and aperture effects, which concern the perception of direction. The challenge of explaining these effects in empirical terms was taken up by two postdocs, Kyongje Sung and Bill Wojtach. Kyongje had gotten his doctorate at Purdue studying how people carry out visual search tasks and was the first card-carrying psychophysicist to join the lab. Bill had gotten his doctorate in philosophy at Duke working on perception; he had come to lab meetings while working on his doctorate and eventually decided to pursue a career that tapped into both philosophy and neuroscience. Bill and Kyongje made a somewhat unlikely scientific pair, but they complemented each other’s skills and eventually showed that perceptions of motion are based on the same strategy as other visual qualities.

They first explored the flash-lag effect, a phenomenon that had been kicked around for decades without agreement about its cause. When a moving stimulus is presented in physical alignment with an instantaneous flash that marks a point in time and space, the flash is seen as lagging behind the moving stimulus. Moreover, the faster the speed of the stimulus, the greater the lag. In the framework we had been pursuing, the flash-lag effect should be a consequence of the same empirical strategy applied to the perception of object speed. To test this supposition, Bill and Kyongje asked whether the amount of lag seen by subjects over a range of speeds is accurately predicted by the relative frequency of occurrence of image sequences arising from 3-D object motion transformed by projection onto the retina. Their first step was to vary the speed of the moving object over the range that elicits a measurable flash-lag effect. They then sampled the image sequences generated by tallying up the frequency of occurrence of the different projected speeds generated by the millions of possible sources moving through the simulated 3-D environment. If the flash-lag effect was indeed a signature of visual motion processing on an empirical basis, then the lag reported by observers for different stimulus speeds should be accurately predicted by the relative positions of different image speeds arising from the influence of this accumulated experience. And it was.

They next explored the perception of direction by studying the changes that occur when moving objects are seen through an occluding frame (an “aperture”). For example, when a rod oriented at 45 degrees moving physically from left to right at a constant speed is viewed through a circular opening that obscures its ends, its perceived direction of movement instantly changes from horizontal to downward at about 45 degrees from the horizontal axis. The simplest phenomenon to explore was the altered direction of motion induced by a circular aperture. The frequency of occurrence of lines that can move across a circular aperture with both ends occluded is strongly biased in favor of the direction orthogonal to the line. Bill and Kyonje showed that this is the direction humans have experienced most often whenever moving lines are seen through a circular aperture.

These empirical explanations of flash-lag and aperture effects again indicate that human experience determines what we see, in this case, experience with retinal projections of moving objects.

Music

By 2009, work on visual perception spanned more than a decade, including six years that I had spent as director of the Duke Center for Cognitive Neuroscience (I had stepped down as chair of neurobiology in 2003). I was 71 by then and beginning to suffer the increasing marginalization that inevitably comes with age. My lab had never been more than seven or eight people, but by 2009, the number had dwindled to three or four. Moreover, I had begun to turn from vision to audition. There were several reasons for this change in direction, the main one being the need to verify the general ideas derived from vision in another sensory modality. Other than vision, audition was the best understood sensory system. Moreover, audition presented a database that was not only useful but fascinating in its own right: music and its poorly understood phenomenology. In vision, it had been easy enough to generate a database of natural scenes that served as a foundation for predicting what we see on the basis of the frequency of occurrence of stimulus patterns. But visual aesthetics—why we like one stimulus more than another—seemed a closed door. In contrast, in audition, the data provided by millennia of musical history provided the needed information to explore the basis of aesthetic appeal in a worldwide art form.

The work on music had begun around 2000 more or less for fun, motivated as well by my longstanding effort to play the guitar halfway decently. Music seemed like an interesting challenge and collaborating with David Schwartz, a newly arrived postdoc, offered an opportunity. David had been trained in psychology at the University of Michigan and had joined the lab without any special preconception of what we might do together. In discussing the possibility of venturing into audition, David, who had considerable experience in music, was game. As a result, together with another postdoc (Debbie Ross), two third-year medical students who had taken off a year to work in the lab (Jonathan Choi and Kamraan Gill), a first-rate graduate student (Daniel Bowling), and a series of undergraduate volunteers, by 2009 we had written several credible papers on music.

The aim was to test whether musical phenomena could be explained empirically on the basis of biology, vocal similarity in particular. The underlying theme was simple: given the ecological benefit of recognizing human vocalization, it made sense to think that the universal penchant for making music might be related to vocal sound signals. The general idea—which we eventually came to call “vocal similarity theory”—was that the closer a musical tone combination is to the harmonic series characteristic of human vocalization, the more humans should have evolved to like the tone combination.

By 2009, the lab had taken a break from vision and was plugging away full bore on audition and music as a way to understand some of its peculiarities. I had certainly not lost interest in vision and was carrying on some work that followed up to what we had been doing. But the grant applications I made to the National Institutes of Health (NIH) on these topics were not well received, as had been the case for a long time. Not only had the NIH come to favor applications with a clinical payoff, but the National Eye Institute (the logical source of support for what I had been doing) was a club to which I did not belong. Older investigators who want to pursue something that is off the beaten path are rightly regarded with suspicion, and pursuing unorthodox ideas about vision and now audition and music was an increasingly hard sell.

Singapore

This was the unhappy situation in the spring of 2009 when George Augustine, a longtime Duke colleague, walked into my office with an unexpected question. By any chance, would I be interested in joining the Duke medical school recently established in Singapore as the director of its neuroscience program? George had taken the opportunity to work at the new school a couple of years earlier and was intent on filling the vacant position in neuroscience with a reasonable person, as was the dean of the school (Ranga Krishnan), and the dean charged with hiring new faculty (Pat Casey). Both Ranga and Pat had moved from Duke to take up positions in Singapore, and both were colleagues for whom I had great respect.

The rationale for Duke’s venture to set up a sister medical school in Asia needs some explaining. Singapore’s colonial heritage meant that, as in Britain, medical school was undertaken immediately after high school as a six-year program, quite different from the U.S. system. Ever anxious to upgrade the country’s system of education, the Singapore Ministry of Education decided it would be wise to invest in an U.S.-style medical school with a doctoral component that could train clinician-scientists (an M.D./Ph.D program). This educational trajectory in medicine had worked in the United States, suggesting that this was a good way to create doctor-scientists who could bring the research more effectively from bench to bedside. Johns Hopkins was Singapore’s first choice for the execution of this goal in the early 2000s. But when Hopkins failed to meet the Ministry’s “mileposts” in a timely way, the deal was called off. The second choice was Duke University Medical School, and by 2005, the project was underway.

To the extent that I thought about this project at all I was, as a bystander, skeptical. But as was obvious by turn of the century, extraordinarily well-educated secondary school students from Japan, China, India, Singapore, and elsewhere in Asia were increasingly joining both undergraduate and graduate schools in U.S. universities. Many of these students would stay in the United States, adding greatly to the energy and expertise of the aging population that had immigrated to the United States from Europe in the first half of the 20th century. Indeed, I had already benefitted greatly from this influx. By establishing sister institutions in Asia and sending faculty to Singapore and other Asian countries, U.S. universities could establish their “brands” abroad, thus faring better in the competitive market for students seeking education in the United States. Duke also could off-load faculty to serve abroad who would be paid by Singapore, creating a financial benefit as well.

I understood little of all this at the time George came by to explore my possible interest. But I had several reasons for taking his question seriously. First, having lost some of its zip, my lab could be reenergized for a few more years. And George didn’t waste any time in pointing out the financial benefits. As any newly hired faculty member, I would receive a generous “startup package” that I could spend on whatever research I wanted to do over the next five years. This was far more support than I could anticipate in the Untied States under the most optimistic scenario. The job also came with a generous salary by U.S. standards, along with additional allowances and prerogatives. As if all this were not enough, relocating in Singapore would be an adventure at a time when life was becoming a bit humdrum. My attractiveness to the Duke–National University of Singapore (NUS) Medical School was that I had plenty of administrative experience and should have no problem organizing a good neuroscience program. Moreover, as an “internationally recognized scientist,” I would lend a measure of credibility to neuroscience at the infant school. To a considerable degree, seeking out recognized names was Singapore’s modus operandi. As a city-state that was striving to join the ranks of other small countries that had major-league scientific clout, it was important to be seen as having some notable players. And, in this respect, Singapore had already done well. An early recruit to advise the government on how to proceed in its overall effort to put biomedicine on the map was Sydney Brenner. Others soon followed, and both the NUS and the NIH-like Agency for Science, Technology, and Research (A*Star) Campus were well stocked with notable expats from the United Kingdom and, to a lesser degree, from the United States.

There was, however, an obvious stumbling block. In thinking over George’s proposition, I was pretty sure that Shannon was unlikely to share my openness to the possibility of moving to Singapore. One of our two daughters was living near us in Chapel Hill with one of our then three grandchildren, and our other daughter was not many hours away in Atlanta with the other two grandkids. In contrast, Singapore was about as far away as one could get on the planet, with a 24-hour plus trip that was debilitating by any standard. I was thus surprised, in broaching the subject when I came home that evening, that Shannon’s response was enthusiastic. She had been planning to retire within a few years as the editorial director of Algonquin Books which she had cofounded 25 years earlier. With retirement looming and the same marginalization beginning to affect her, an adventure during which she could continue her work remotely but gradually cut the cord with Algonquin appealed to her. I think she also sensed that it would be a good thing for me, perhaps fending off the depression that she imagined might afflict me as things inevitably continued their slow decline at Duke.

I had left it with George that Shannon and I would think hard about the possibility and get back to him. We talked about little else over the next few days, coming to the conclusion that there wasn’t much to lose and a good deal to be gained, at least for me. So in June 2009, we took the first of what would be many trips to Singapore, this one simply to look over the lay of the land. In truth, I am not sure Shannon or I could have found Singapore on the map and our knowledge of the island and its cultural makeup was nonexistent. But Singapore is a thoroughly modern, beautifully organized city-state in which physical dilapidation, crime, and U.S.-style poverty are virtually unknown, and it as cosmopolitan as New York or London without the ethnic tension. The only obvious downside to emigrating was the unhappiness of our daughters, both of whom were upset about our being so far away (it hadn’t occurred to us that in their view we were “elderly,” which no doubt contributed to their concern). Nonetheless, they eventually relented. We found a sitter for our house in Chapel Hill in case things didn’t work out and, by September 2009, had packed up and were on our way.

A truism is that adjusting to Singapore is “Asia lite.” A problem for any couple, however, is that while the spouse with a full-time job has some sense of purpose and is pretty well insulated from loneliness, that is not the case for the partner who doesn’t have work. Although Shannon had plenty to do online for Algonquin Books, it is quite different being in a workplace and sitting in an apartment using the Internet and Skype. It was soon clear that Shannon would be condemned to the life of an expat spouse, of whom there were a great many in Singapore. Although many became good friends, it was clear from the outset that Shannon’s experience would be quite different from mine.

The Duke medical school in Singapore turned out to be a plus for both for Singapore and Duke. Nonetheless, its success was achieved only after an enormous amount of work by Sandy Williams (then dean of the Duke medical school in the United States), Pat Casey, and other “pioneers” during the initial years of the project. The Duke–NUS Graduate Medical School officially opened in 2006, housed in what previously had been a barracks close to the site where the new school was being built, at Singapore’s expense, and next to Singapore General Hospital with its excellent clinical faculty. Twenty-five students were taken into that first year’s class and began their training in makeshift circumstances. But it worked, and in 2008, the faculty, students, and staff moved into the newly constructed school.

Despite having missed the hard part of getting the school going, my entry into professional life at Duke–NUS was not altogether easy. Everyone’s best intentions notwithstanding, I had to set up a new lab and hire a new staff. The only person I brought with me from the United States was Dan Bowling, the graduate student working on music for his doctorate. Dan arrived in Singapore a few weeks before we did and was an enormous help. But the new lab had to be remodeled and new equipment bought. Money was no problem, but ordering things, many of which had to come from abroad, was not simple, and it was a good three months before we could actually get to work. In the meantime, I was learning the administrative ropes of the new school and the faculty already in place.

Both Pat Casey and Ranga Krishnan, the newly appointed dean of the school, were excellent administrators, but neuroscience in Singapore was a moving target. Ranga told me a few weeks after I arrived that, if I was willing, there was another component to the job I had signed on for, namely, becoming executive director of the A*Star neuroscience program in Singapore. A*Star was more or less the equivalent in Singapore of the NIH, which is to say a collection of research centers on its own campus. This codirectorship made a certain amount of sense, and I was curious to see another side of science in Singapore. The A*Star neuroscience director had been Colin Blakemore. Colin, however, had been in Singapore only part time, and the A*Star administration seemed glad to welcome a full-timer in this interesting if ultimately frustrating position.

Before arriving, I had begun to place ads for postdoctoral fellows and research assistants (RAs). (Even though I had signed for what could be a five-year stint, I thought it unwise to take on any new graduate students because it was unclear how long my tenure might actually be.) In this I was lucky, and before long, in addition to Dan, I had three RAs, one very good postdoc, and two more on the way. The RAs and the postdoc who came first were from local institutions, but because money was in short supply in the United States for the kind of work I was doing, postdocs from abroad were not hard to come by. And so, by the late fall of 2009, things in the lab were pretty much set to go.

Research in Singapore

Having gotten things set up in Singapore, the question once again was what to do next. There were two attractive avenues to pursue now that I had plenty of support to do whatever I wanted without having to get more grant money in the United States. The first was further understanding music in biological terms. The second was to press on with visual perception, in particular the mechanism that translated the frequency of stimulus occurrence into the qualities we actually see.

To take music first, the basis of consonance and dissonance, the rationale for scales, the universality of a few scales in music, the rationale for tuning, and octaves as a musical framework all remained largely unexplained. The challenge was to examine whether these issues could be explained in biological terms. Kamraan Gill, the medical student who joined the lab for a year in 2008, had shown that of the billions of possible scales that humans could have used to make music, only a few dozen were in fact employed. The payoff was that these few scales were empirically ranked at the top of the list when the similarity of all possible scales was compared to the uniform harmonic series that characterize human vocalization. This finding strongly supported the idea that humans prefer tonal combinations that mimic conspecific vocalization.

A second encouraging observation came from Dan Bowling’s work on the expression of emotion in musical tones. It had been accepted for centuries that major scales generally are used to express happy, excited, or martial feelings, whereas music in a minor mode expresses sadness, lethargy, and a subdued state of mind. Dan showed that vocalization in these various states indeed tracked the tonal intervals found in major and minor scales.

These successes encouraged exploring further links between music and human vocalization. One possibility was looking for a parallel between the music and speech of cultures whose languages used tones to indicate meaning, such as Mandarin, Vietnamese, and Thai. These linguistic data then could be compared with the characteristics of classical music in various cultures. Singapore was an ideal place to carry out such studies because of the polyglot population and extensive library of Asian musical scores housed at the NUS music library. By good fortune, two of the research assistants I had hired, both graduates of NUS, were well prepared for this work. Han Shiu ‘Er was a native Singaporean fluent in Mandarin and knowledgeable about music, and Janani Sunderarajan was fluent in Tamil and an expert in the classical Carnatic music characteristic of South India. Despite some bumps in the road, they both took to the project and were soon documenting the relationship between classical Asian musical scores in tone and nontone languages. Based on our “vocal similarity theory,” the supposition was that music in tone and nontone language cultures should be quite different. And this turned out to be the case. The music of tone language cultures uses greater pitch differences than nontone languages, which use smaller intervals and less frequent reversals of pitch direction. In contrast to classical European music, these findings were common to the classical music of China, Vietnam, and Thailand.

In another study, we examined the idea that musical consonance depends on recognizing and attending to human speech. Based on the work that Gill had carried out on scales, we supposed that the attraction to tone combinations would reflect the degree to which they represented a harmonic series, and vice versa in the case of dissonant tone combinations. In music, melodies and harmonies make up the tone combinations that can be simple dyads (a combination of two tones) or more complex chords. The idea was that when a tone combination in music more closely approximated a complete harmonic series—for example, an octave or a perfect fifth—the more consonant it should be. Conversely, tone combinations that less faithfully mimicked a harmonic series—for example, a minor second or a major seventh—would be relatively dissonant. Again, this turned out to be the case, as documented in Dan’s thesis in 2012 and the papers that followed from it.

About the same time, another postdoc arrived in the lab with the intention of pursuing empirical explanations in music. Brian Monson had finished a doctorate in speech analysis at the University of Utah and, as a member of the Mormon Tabernacle Choir, was well versed in vocal music. He took up a project that examined more specifically whether the same ideas that had been useful in rationalizing visual perception applied to audition. The goal was to ask whether the way we perceive basic acoustical features, such as loudness and pitch, are predicted by the empirical characteristics of speech. If trial-and-error experience is also the basis for perception of tonal sounds arising from unknowable physical sources, then one would expect the frequency of occurrence of a physical intensity or frequency (the physical correlates of sound stimuli) to underlie the loudness and pitch values we actually hear. Brian succeeded in confirming this idea by correlating the frequency of occurrence of intensities and frequencies in speech with classical psychophysical functions in audition.

Nonetheless the major preoccupation of the lab continued to be vision. The piece in the puzzle that had been left more or less in limbo when the lab moved to Singapore was the mechanism underlying the empirical association between visual experience and visual perception. The percepts we become aware of never accord with physical measurements, and the issue was how to explain this disconnection in neurobiological terms. Now that I had the wherewithal to hire new collaborators who had the talent in the needed computational domains, empirical vision joined music and speech as a mainstream in the laboratory.

The initial foray into how empirical vision might work was undertaken by a bright research assistant named Mike Hogan who was taking a year off after graduating from Hampshire College. Although what he did was entirely bootstrapped, the goal was to use artificial neural networks instructed by trial-and-error experience rather than algorithms, asking whether evolved networks showed evidence of “perceiving” visual qualities in the strange way that humans did. The best visual quality for this purpose was the lightness values seen in response to luminance patterns. Thus, Mike set about training simple neural networks in artificial environments in which reproductive success depended on responding to light intensities.

In this he was soon joined by two postdoctoral fellows, Cherlyn Ng and Yaniv Morgenstern. Cherlyn had gotten her doctorate in molecular biology and had done a postdoc in cancer research. But she was unenthusiastic about the sort of work that the field demanded and wanted to try her hand at neuroscience. Yaniv, in contrast, had already trained in neuroscience in Canada and arrived after finishing a postdoc in Montréal. He was adept at programming and what Mike had started during his year in the lab Yaniv took over with a much stronger background. The three collaborators became increasingly good at crafting a project on the perception of light intensity that began to make some sense. The idea was to use simple luminance patterns received by a sensory array that could then inform a feedforward neural network whose evolved connections and output signified the “perception” the network had chosen as a basis for its “behavior.” Populations of such networks used trial and error to continually improve their responses over time without any indication of what problem they were trying to solve. I/we believed that the inability to measure the physical world using biological sensors was the major problem vision had to contend with and that this empirical approach was the only way a nervous system could deal with the intractable complexity of its owner’s environmental niche.

All the while, I was of course learning a great deal about Singapore. The theme in transforming Singapore from an underdeveloped island to a major player had always been money. And it was this aspect of science in Singapore that I struggled with unsuccessfully in my role as the director of the neuroscience program at the Duke–NUS Medical School and as the executive director of the A*Star neuroscience program. In both cases, the stumbling block was freedom to do “blue sky” science, which was constrained by the government’s preeminent concern with the economy. When I arrived in 2009, there was some enthusiasm for the idea that excellence in basic science would differentiate Singapore from countries wedded to human health as the goal of biomedical research. Over the four years I was in there, however, there was a decided shift from the idea that Singapore had the financial wherewithal to pursue both avenues to the view that basic research should contribute to the bottom line. The Ministry of Finance came to have increasing control over science policy, and the climate for carrying out basic science by the time I left was pretty much like every other developed country. Although I left for personal reasons, given my research, I would have had a tough time getting grants in Singapore had I stayed much longer.

What made me call it quits after four years was that Shannon was now 10,000 miles away, having returned to Chapel Hill at the end of 2012. I had no counter to her reasons for going home other than the self-serving desire to go on doing research in what for me was a still a comfortable environment. So in September 2013, I returned to Duke, where I took up more or less where I had left off four years before. The reality, however, was that I was now an elder statesman whose presence was of no particular value to a new contingent of neuroscientists and administrators.

Back at Duke

When I came back to Duke in the fall 2013, I was prepared for a less-than-enthusiastic welcome. At 75, I would have been expected to become emeritus and to quietly fade into the academic sunset. But this was something I did not want to do. I had been forewarned by Ranga Krishnan, the astute dean of Duke–NUS Medical School, that becoming emeritus was rarely a wise move. He pointed out that the only emoluments that came with that status at Duke were an email account and the right to park on campus if one could find an empty space. But in seeking some other arrangement, I found out that things were not so simple. I couldn’t transfer the considerable research money left in my account in Singapore to Duke, meaning that I would be starting all over seeking grant support, long the measure of an individual’s value to a department of basic science. And although I had imagined returning to the Department of Neurobiology at Duke where I had been chair for 13 years, after a decade in absentia, I had few friends there.

The Neurobiology Department had fallen on relatively hard times over those years. Jim McNamara had taken over as chair when I stepped down in 2003. As a neurologist and leading researcher on the genetics of epilepsy, he was an ideal choice in an era that had become heavily biased toward clinical relevance and grants that advanced the human health agenda. But events conspired against him. Several of the faculty members that I had hired in the 1990s were now mature scientists of considerable stature and were looking at other jobs. In addition, perhaps my most successful hire—Larry Katz—died of malignant melanoma in 2005. The combination of Larry’s death, the departure of Mike Ehlers to Pfizer Pharmaceuticals and Guo Peng Fong to MIT were major hits. At the same time, David Fitzpatrick, a highly regarded vision scientist had moved on to become director of the Duke Institute for Brain Sciences. The same course was taken by Michael Platt, another excellent faculty member, a few years later when David left to become director of the new Max Planck Institute in Florida.

In all the hiring I had done at Duke and then in Singapore, I had sought entry-level scientists with promise. Although some of these hires failed, the batting average was bound to be better than trying to poach senior faculty from other institutions. Given the complications of moving, leaving children’s schools behind, and distancing oneself from long-standing friendships, most senior researchers who put themselves on the market actually are trying to force their home universities to match an attractive outside offer. And most universities, unless the faculty member is a real pain in the ass, are happy to meet this demand rather than take on the far greater trouble and expense of finding a replacement. But in replacing these departures at Duke, Jim had recruited senior faculty and never hit pay dirt, and a new chair was being sought to invigorate the department.

All this transpired while I was in Singapore, but I knew that the search for a new chair had not gone smoothly. In the end, the job was accepted by Stephen Lisberger, a very good vision scientist from the University of California at San Francisco. I had never met Steve, but he had a reputation of being hard-nosed. Indeed, the only interaction Steve and I had had was his complaint several years earlier that a paper of mine he had overseen as an editor probably should not have been accepted (this was the first paper on music in 2003, and his complaint was not entirely without merit).

Although Steve never said so directly, it was clear from third parties that I would not be particularly welcome in my old department. This lack of enthusiasm was reasonable as I had noted in seeing other ex-chairs find a home: there is no joy in having someone previously in authority looking over one’s shoulder, whether in fact or imagined. Thus, I probably would have taken the same view had I been in Steve’s shoes. In any event, this left me stateless, so to speak, as appointments at Duke are generally made in departments. But to the credit of the search committee, Steve did an outstanding job setting the department to rights and extracting the substantial money from the university needed to do so. He hired good junior people and was deeply dedicated to the details of running the department, something that I always found burdensome and often neglected.

The solution for me finally emerged when I asked the provost, Peter Lange, what he saw as the alternatives. He pointed out that the obvious answer was to be hired in the Duke Institute for Brain Sciences (DIBS), which was then being run by Michael Platt whom I had recruited to Neurobiolgy some years earlier. As an “institute” at the university rather than a department, DIBS could hire in its own right. Michael agreed to this arrangement and gave me a small space in the Center for Cognitive Neuroscience, which was also under his aegis. I thus would be a department-less “research professor” but with full faculty standing. Because I had no grants and really didn’t want to rejoin that competition, I was happy enough with the arrangement at no salary. This amorphous status served my intention to remain in the neuroscientific mix of the university, teaching and taking pokes at fatuous arguments in seminars (not a wise priority, but one that I had always enjoyed). And there was a lot of science still to be finished up with my erstwhile collaborators from Singapore.

Having resettled, the first order of business was to establish courses in the two domains that remained my interests, music and vision. A new fashion in teaching had taken hold by 2013 was massive open online courses (MOOCs) and Duke had already partnered with Coursera, one of the major players in this new way of educating. The idea of presenting material on vision and music for free to a worldwide audience was immediately attractive. My first effort in 2013 was a MOOC on vision, with the goal of putting together a course based on a book that Beau Lotto and I had recently written (Why We See What We Do Redux, Sinauer, 2011) whose message would be relatively easy to convert into an online course. Thus, I enlisted two savvy undergraduates who knew enough about the video editing software to put together a beta version of the course on our own (a year later, I redid the course with professional help). Having tested the waters, I did the same thing for music, coupling another MOOC with a book on music I was then writing.

Not writing grants was a huge relief after 45 years of begging for money in an increasingly unfavorable environment for people like me who were interested in issues outside the mainstream. Although lacking grants meant that any new work had to be low cost (as indeed much of it already was in Singapore even when the lab was well heeled), this was no great impediment since I could tap into a sizable slush fund that had accumulated over the years. One order of business was to finish up Yaniv Morgenstern’s project, showing that the same ideas explaining the relationship between light intensity and the perception of lightness also applied to the relationship between spectral distribution in color perception. At the same time, Yaniv extended the work on lightness based on the experience of evolving neural networks. These papers were published in 2014 and 2015 and were backed up by a more general account of this overall theme coauthored by Yaniv and Bill Wojtach.

Another piece of unfinished work from Singapore was a theoretical paper written with Chidam Yeggapan on the geometrical basis of color vision. The gist of Chidam’s argument was that solving the four-color map problem in a 2-D image on the retina was basically a geometrical challenge. In a 2-D space, the evolution of color vision must contend with the four-color map problem as it pertains to light spectra in images. At the same time, color vision must be able to identify all spectrally different equiluminant points on a 2-D plane. These dual goals can be achieved by two pairs of direction vectors that give rise to four color classes defined by four unique hues that are pair-wise opponents. Despite its complexity, I thought Chidam’s paper was both ingenious and correct. Nevertheless, the paper proved to be almost impossible to publish despite its originality—or perhaps because of it—and was anonymously rejected by all of the first-line vision science journals we sent it to. It was not until 2016 that this work saw the light of day in a newly minted vision journal that was no doubt anxious to take any paper by credible authors.

Another piece of unfinished work in vision was binocularity. Cherlyn Ng had begun to explore the idea that there might be a simpler way to explain fusion, stereopsis, and the puzzle of ocular dominance. Uniting the right- and left-eye views usually was tackled in terms of matching corresponding image points, although exactly how this could be accomplished remained debatable. Another possibility was that different levels of activity at anatomically corresponding retinal points were being used to produce a sense stereoscopic depth. Once again, this work proved difficult to publish.

There was much to finish up on music as well. Dan Bowling and I undertook a short review that summarized work on the hypothesis that consonance and dissonance were intimately related to the biological advantages of recognizing and attending to the uniform harmonic series that characterize human vocalization. The initial intent was a more extensive article that would pull together all aspects of musical tones. But Dan and Kamraan Gill argued correctly that more evidence was needed, particularly with respect to musical chords. Although consonance and dissonance had long been studied in the context of dyads (i.e., musical intervals consisting of a lower reference note and a higher tone), there was almost no work on higher-order chords. This deficiency led to a further project on triads and tetrads, the three- and four-tone chords familiar in musical harmony. Dan had begun this work in Singapore testing musically literate and naïve subjects on their relative attraction to musical chords. But there was much more to do and, without any particular help from me, the two of them forged ahead and analyzed a large set of three- or four-note chords with respect to their appeal to listeners and their physical similarity to a harmonic series. This work was published in 2019 and Dan, now at Stanford, and I are still trying to understand musical tuning in biological terms as I write this.

Summing Up

To go back to the beginning, the foundation for thinking about the nervous system when I was a first-year medical student in 1960 was primarily knowledge about nerve cells and neural signaling based on work carried out over the preceding few decades by Hodgkin, Huxley, Kuffler, and Katz with their collaborators and students. This remarkable body of research had led to a reasonable understanding of how information in the nervous system is transferred by action potentials and conveyed to other neurons by synaptic transmission. Although a wealth of detail about these processes has been added since, this basic understanding of neural function at the cellular level remains much the same as when I first learned it.

In contrast to the clarity of what is known about neural signaling, the functional significance of brain structures, their complex interconnections, and how they determine human behavior remains poorly understood. Why, then, despite the enormous increase in information about the properties of neurons in different regions, their connectivity, their transmitter pharmacology, and the behavioral situations in which they become active, do neuroscientists remain relatively ignorant about perception and other higher-order behaviors that now interest us most?

The reason, at least in part, is the absence of some guiding principle or principles that would help sort out the neural underpinnings of perceptual, behavioral and cognitive phenomenology. One doesn’t have to be steeped in history to recognize that other domains of biological science have typically advanced under the banner of some overarching framework. The complexity of the human nervous system notwithstanding, when all is said and done, our brains and the rest of our nervous systems are arguably doing just one basic thing: using trial and error to associate sensory information with successful behavior by neuronal connectivity. As a result, the neuronal associations underlying successful behavior in response to stimuli wax over the eons whereas unsuccessful associations wane, eventually leading to the brain circuitry humans and other animals have today. By the same token, modulating neuronal connectivity by activity-dependent plasticity promotes learning during the lives of individuals. All that is needed to implement these strategies is plenty of time and a way of providing feedback about the relative success of behavior. The history of life on earth has provided ample time and natural selection has offered a wonderfully powerful mechanism for assigning credit to successful behavior.

At 82, I have not quit promoting this explanation of nervous systems. Brains seem to be logically unfathomable skeins of neuronal connections that embody the ever increasing empirical associations that have kept animals going strong for more than 500 million years and counting.

Selected Bibliography

Bowling DL, Gill K, et al. (2010) Major and minor music compared to excited and subdued speech. J Acoust Soc Am. 127(1): 491–503.

Bowling DL, Purves D (2015) A biological rationale for musical consonance. Proc Natl Acad Sci. 112: 11155–60.

Coppola D, Purves D (1996) The extraordinarily rapid disappearance of entoptic images. Proc Natl Acad Sci. 93: 8001–04.

Gill KZ, Purves D (2009) A biological rationale for musical scales. PLoS ONE. 4: e8144. doi:10.1371/journal.pone.0008144.

Howe CQ, Lotto RB, Purves D (2006) Comparison of Bayesian and empirical ranking approaches to visual perception. J Theor Biol. 241: 866–75.

Howe CQ, Purves D (2002) Range image statistics can explain the anomalous perceptionof length. Proc Natl Acad Sci. 99(20): 13184–88.

Howe CQ, Purves D (2005) Natural scene geometry predicts the perception of angles and line orientation. Proc Natl Acad Sci. 102(4): 1228–33.

Howe CQ, Purves D (2005) Perceiving Geometry: Geometrical Illusions Explained by Natural Scene Statistics. New York: Springer.

Hume RI, Purves D (1981) Geometry of neonatal neurones and the regulation of synapse elimination. Nature. 293: 469–71.

Hume RI, Purves D (1983) Apportionment of the terminals from single preganglionic axons to target neurones in the rabbit ciliary ganglion. J Physiol. 338: 259–75.

LaMantia A-S, Pomeroy S, Purves D (1992) Vital imaging of glomeruli in the mouse olfactory bulb. J Neurosci. 12: 976–88.

Lichtman JW, Magrassi L, Purves D (1987) Visualization of neuromuscular junctions over periods of several months in living mice. J Neurosci. 7: 1215–22.

Long F, Yang Z, Purves D (2006) Spectral statistics in natural scene predict hue, saturation, and brightness. Proc Natl Acad Sci. 103(15): 6013–18.

Lotto, RB, Purves D (1999) The effects of color on brightness. Nature Neurosci. 2: 1010–14.

Njå A, Purves D (1977) Re-innervation of guinea-pig superior cervical ganglion cells by preganglionic fibres arising from different levels of the spinal cord. J Physiol. 272: 633–51.

Purves D (1975) Functional and structural changes in mammalian sympathetic neurons following interruption of their axons. J Physiol. 252: 429–63.

Purves D (1988) Body and Brain: A Trophic Theory of Neural Connections. Cambridge, MA: Harvard University Press.

Purves D (2010) Brains: How They Seem to Work. New York: Pearson–Financial Times Press.

Purves D (2019) Brains as Engines of Association: An Operating Principle for Nervous Systems. New York: Oxford University Press.

Purves D, Augustine GA, Fitzpatrick D, Hall W, LaMantia A-S, White LW (2017). Neuroscience, 6th edition. New York: Oxford University Press.

Purves D, Hadley RD (1985) Changes in the dendritic branching of adult mammalian neurones revealed by repeated imaging in situ. Nature. 315: 404–06.

Purves D, Hume RI (1981) The relation of postsynaptic geometry to the number of presynaptic axons that innervate autonomic ganglion cells. J Neurosci. 1: 441–52.

Purves D, LaMantia A (1993) Development of blobs in the visual cortex of macaques. J Comp Neurol. 334: 169–75.

Purves D, Lichtman JW (1985) Geometrical differences among homologous neurons in mammals. Science. 228: 298–302.

Purves D, Lichtman JW (1985) Principles of Neural Development. Sunderland, MA: Sinauer Associates.

Purves D, Lotto RB (2003) Why We See What We Do: An Empirical Theory of Vision. Sunderland, MA: Sinauer Associates.

Purves D, Lotto RB (2011) Why We See What We Do Redux. Sunderland, MA: Sinauer Associates.

Purves D, Lotto B, Polger T (2000) Color vision and the four-color-map problem. J Cog Neurosci. 12(2): 233–37.

Purves D, Monson BB, Sundararajan J, Wojtach WT (2014). How biological vision succeeds in the physical world. Proc Natl Acad Sci. 111: 4750–55.

Purves D, Williams MS, Nundy S, Lotto RB (2004) Perceiving the intensity of light. Psycholog Rev. 111: 142–58.

Purves D, Wojtach WT, Lotto RB (2011) Understanding vision in wholly empirical terms. Proc Natl Acad Sci. 108(3): 15588–95.

Purves D, Yegappan C (2017) The demands of geometry on color vision. Vision.1(9). doi:10.3390/vision1010009.

Riddle DR, Gutierrez G, Zheng D, White LE, Richards A, Purves D (1993) Differential metabolic and electrical activity in the somatic sensory cortex of juvenile and adult rats. J Neurosci. 13: 4193–213.

Schwartz D, Howe CQ, Purves D (2003) The statistical structure of human speech sounds predicts musical universals. J Neurosci. 23(18): 7160–68.

Sung K, Wojtach WT, Purves D (2009) An empirical explanation of aperture effects. Proc Natl Acad Sci. 106(1): 298–303.

Williams, SM, McCoy AN, Purves D (1998) An empirical explanation of brightness. Proc Natl Acad Sci. 95(22): 13301–06.

Wojtach WT, Sung K, Truong S, Purves D (2008) An empirical explanation of the flash-lag effect. Proc Natl Acad Sci. 105(42): 16338–43.

Yang Z, Purves D (2003) A statistical explanation of visual space. Nature Neurosci. 6: 632–40.

Yang Z, Purves D (2004) The statistical structure of natural light patterns determines perceived light intensity. Proc Natl Acad Sci. 101(23): 8745–50.

A complete list of publications is available at http://www.purveslab.net.

Larry R. Squire

BORN:

Cherokee, Iowa

May 4, 1941

EDUCATION:

Oberlin College, BA (1963)

Massachusetts Institute of Technology, PhD (1968)

APPOINTMENTS:

Fellow, Albert Einstein College of Medicine (1968–1970)

Assistant Research Psychobiologist to Distinguished Professor, Department of Psychiatry, University of California, San Diego (1970–Present)

Research Career Scientist, Veterans Affairs Medical Center, San Diego, California (1980–Present)

Distinguished Professor of Neurosciences, University of California, San Diego (1993–Present)

Distinguished Professor of Psychology, University of California, San Diego (1996–Present)

Affiliate, Neurobiology Section, University of California, San Diego (2005–Present)

HONORS AND AWARDS (SELECTED)

Elected, National Academy of Sciences, USA (1993)

Elected, Society of Experimental Psychologists (1993)

Distinguished Scientific Contribution Award, American Psychological Association (1993)

Dana Foundation Award for Pioneering Achievements in Health (1993)

President, Society for Neuroscience (1993–1994)

William Middleton Award, Department of Veteran Affairs (1994)

McGovern Award, American Association for the Advancement of Science (1994; 2004)

Karl Spencer Lashley Award, American Philosophical Society (1994)

Elected, American Academy of Arts and Sciences (1996)

Elected, American Philosophical Society (1998)

Elected, Institute of Medicine (2000)

Metropolitan Life Foundation Award for Medical Research (2000)

Kuffler Lectures, University of California, San Diego (2005)

Howard Crosby Warren Medal, Society of Experimental Psychologists (2007)

Doctor Honoris Causa, University of Basel, Switzerland (2010)

NAS Award for Scientific Reviewing, National Academy of Sciences (2012)

Goldman-Rakic Prize, Brain & Behavior Research Foundation (2012)

Doctor Honoris Causa, Oberlin College, Oberlin, Ohio (2013)

Lifetime Contribution Award, National Academy of Neuropsychology (2017)

Larry Squire has been a pioneer in elucidating the structure and organization of mammalian memory. He provided the first evidence that the resistance of memory to disruption can develop over a period of years in humans. This finding implied a memory consolidation process that reflects, not rapid transition from a labile to a stable, long-term state but gradual reorganizfation within long-term memory itself. He showed in rats, monkeys, and humans that, by such a process, memory becomes gradually independent of the hippocampus and intrinsic to neocortex. With Stuart Zola, and working with nonhuman primates, he discovered the anatomical components of the medial temporal lobe memory system: the hippocampus plus the adjacent, and previously neglected, entorhinal, perirhinal, and parahippocampal cortices. Building on early work with his student Neal Cohen, he established the biological distinction between declarative and nondeclarative memory and the idea that different kinds of memory depend on different brain systems. Through studies of memory-impaired patients, classical eyeblink conditioning, and memory-guided eye movements, he and his colleagues identified conscious awareness as key to the distinction between declarative (aware) memory and nondeclarative (unaware) memory. The work is a rare example of bringing both human and animal studies, and multiple methods, to the science of brain structure and function.

Larry R. Squire

There was nothing particular in my background to suggest that I might become a scientist. Both my parents and all four grandparents were from Grinnell, Iowa. My maternal grandfather was a long-time professor of speech at Grinnell College, and my maternal grandmother was an accomplished pianist and harpist. My father’s circumstances were more modest. His father ran a gas station, and my father worked his way through Grinnell College, majoring in physics. The family left Iowa for New Jersey and then New York State soon after I was born and a few years later landed in Columbus, Ohio, where my father founded a successful, wholesale heating and air conditioning company. At one point he served as president of his national trade association. Later in life, leaving the daily tasks of the business to others, he attended Ohio State University to obtain a doctorate in finance, taught a course at a local university for many years, and produced two instructional books for contractors in retail business. We took a number of camping trips, together with other boys, including one epic trip down the Ohio and Kentucky rivers. My father and I were both Eagle Scouts. He was always an advocate of hard work and had strong opinions, but as a Goldwater Republican his opinions usually differed from mine.

My mother was more easygoing. She ran the house and looked after my younger sister and me. She enjoyed sports (had a basketball trophy from high school), did ceramics, and had a talent for word games. All through high school, I could never beat her at anagrams or categories (write down city names, rivers, birds, and so on beginning with a particular letter). She was completely noncompetitive. I beat her once when I prepared for a game of categories by studying the dictionary and then suggested that we use the letter R. When I won, she made no comment and seemed not to notice that anything unusual had happened. Once she attended a baby shower for a niece and joined in a game of anagrams (make as many words as possible from some longish title words). After several minutes, the hostess asked, “Does anyone have more than 20?” “Oh, I have about 200,” my mother said. She explained to me later, “They gave you all the vowels.”

Early Schooling

My mother took a close interest in my early schooling where, as an early reader, I was mostly unengaged. After I skipped the second half of first grade at public school, she enrolled me in the supposedly progressive university school, affiliated with Ohio State. There, the class was divided into three reading groups—advanced, middle, and slow. Still the early reader, I was assigned to tutor the slow group. I have always viewed this as unfortunate, because it set me apart from the other students and encouraged the idea that I had special academic talent. In fact, as I later learned, reading skills develop at different rates, and the slower kids turned out fine. In any case, my mother had had enough and with third grade I began at the Columbus Academy, a private day school for boys (grades 1 through 12). I liked it there. The teachers were excellent, and I was glad to be in the midst of very capable students.

At the Academy, the junior year public speaking course required each of us to deliver a talk to the student body. As I rose through the grades, hearing splendid talks on such subjects as the United Nations, bats, and the ascent of Mt. Everest, I harbored the idea that I would transfer to a different school that year. The thought of speaking in front of a couple hundred people was terrifying. When my time came, I proposed the topic “Science and Religion.” Fortunately, the instructor was discouraging (“a bit too large”), and in the end, I managed to deliver on the topic of hypnosis, perhaps an early sign of interest in cognitive science.

I had no real plans for college except to go to a good place that was coeducational. (In 1959, most of the noted east-coast schools enrolled only men.) One day my mother came across a ranking of the top 10 schools in my category. The list began with Oberlin, then Swarthmore, and then others including Reed, Grinnell, and Carlton. Oberlin was first, so I visited and then applied only there. It proved to be a fine choice. The faculty was dedicated and accessible, music was everywhere (thanks to the Conservatory of Music), and the students were a stimulating mix of impressive and interesting people (many from the east coast) who, like me, had opted for a small, active community over a larger school with clubs and fraternities. Among the faculty, I was most influenced by Norman Craig (chemistry), Lee Henderson (psychology), and Celeste McCollough (psychology), discoverer of the McCollough visual aftereffect. She taught a riveting course in what was then called physiological psychology. Neuroscience was not yet a curriculum term.

Graduate School

When it came time to think about what to do next, I recognized that I was deeply interested in brain and cognition. If I were going to learn more, I would need to go to graduate school. I did not have enough background at that point to suppose that I was preparing to be a scientist. Rather, I imagined becoming a scholar, an academic, perhaps a professor at a place like Oberlin.

The direction I was headed in looked even better after spending the summer after Oberlin (1963) as an assistant to Dr. McCollough, who was doing a sabbatical term at McGill University in Montreal. I undertook a largely unsuccessful project involving autonomic conditioning in the rat, but I was able to meet Donald Hebb, Peter Milner, and a number of talented graduate students, including Graham Goddard and Philip Liss. The highlight of the summer was a visit from Jerzy Konorski, director of the Nencki Institute of Experimental Biology in Warsaw and author of the 1948 book Conditioned Reflexes and Neuron Organization. He gave a chalk talk, and the students told him about their projects. I had no experience in presenting but was asked to take a turn as well, so I told him about my project, which had no results. He listened politely, hurrying me along when I described irrelevant details and expressing interest in the overall idea. I returned from McGill through Washington, D.C., where I participated in the March on Washington and heard Martin Luther King deliver “I Have a Dream.” The eloquence of his address distinguished it from the many other speeches made that day, but only later was I able to appreciate that I had been present at an historic occasion.

I was accepted at the three graduate programs I applied to and had decided on the Department of Psychology at Stanford. I was especially interested in memory and knew of two faculty there, J. Anthony Deutsch and Karl Pribram, who had written on the subject. As it turned out, Tony Deutsch was not working on memory at the time, and Pribram was remote in the medical school. There were fine faculty, and a large clinical program, but there was nothing resembling neuroscience and no program for the biological side of psychology.

I did find a card room and fell into regular poker playing (no limit, California lo ball). This was pretty absorbing, and I was good enough at it to match my stipend. But, by the end of the year, I had not connected to any faculty except a prominent neuroendocrinologist, Seymour (Gig) Levine, who was a regular at the card room and known to us there simply as “Doc.” I only learned who he actually was later in the year when one day I saw him parking near the building where he was to chair our group’s weekly lunch meeting. I greeted him with “Doc, do you work around here?” Such was the extent of my disconnection from Stanford. At the year-end evaluations, I was 1 of 9 in our class of 27 who was invited to stay one more year for a terminal master’s degree.

Someone asked me once why I didn’t give up at this juncture, but I guess this didn’t occur to me. Stanford at the time was not a good match for my interests, and in truth, I hadn’t yet really engaged in graduate school. After a couple weeks of disorientation and reflection, I wrote to MIT where I had been accepted initially and asked if I might “reactivate” my admission after I completed the master’s degree. In what proved to be the signal event of my career, I soon received a letter saying to forget the master’s and that I could come in the fall. So, in 1964, off I went to Cambridge. From Stanford, I took my poker winnings and the beginnings of what became a lifelong hobby.

MIT was what I had hoped for. The program was housed in a single building, there was considerable esprit among the students, and there seemed to be a sense of common purpose across the entire community. Everyone’s work was relevant and interesting, and most of it involved what would soon be called neuroscience. The faculty included Peter Schiller (see Volume 7 in this series), Charlie Gross (Volume 6), Richard Held (Volume 6), Emilio Bizzi (Volume 6), the distinguished neuroanatomist Walle Nauta, and a research associate, Harvey Karten. The department head Hans-Lukas Teuber, a remarkable man, had assembled the faculty himself (then as a Department of Psychology, later renamed the Department of Brain and Cognitive Sciences). He had encyclopedic knowledge of the literature and was a gifted lecturer. The weekly Friday colloquia, which drew scientists from the Boston area, appeared to be organized entirely by Teuber, and he introduced most of the speakers himself. He inspired a whole generation of students to pursue what now would be called systems neuroscience (cellular and molecular neuroscience came to the department later). He died in 1977 in a swimming accident at the age of 60.

At MIT, I made some missteps as I learned what was expected of a graduate student and a young professional. On one occasion, the department scheduled a practice session for the people who would be speaking at an upcoming meeting. Afterward, one of the faculty asked me, “Why weren’t you there?” “Well,” I said, “I know what everyone is doing.” He patiently explained that the purpose of the session was not for my benefit but for me and others to provide feedback and encouragement to the speakers. On another occasion, I attended a large meeting where a speaker was to present on spreading depression, a technique I had used but with a different interpretation (Squire and Liss, 1968). After the session, one of my faculty found me and asked, “Where were you?” I replied, “I know his experiments and what he was going to say, so I went to another session I was interested in.” With some dismay, he explained that I needed to be there to represent my position and potentially defend it. All of this seems so obvious now that it is difficult to recognize myself in these stories.

I eventually developed a project documenting the effects of cholinergic and anticholinergic drugs on memory in rats (Squire, 1969). It was not unusual in those days for graduate students to construct their thesis problems semi-independently and outside the research program of any particular faculty. Peter Schiller kindly agreed to be my adviser, despite not being especially interested in my topic. Professor Teuber seemed eager to see me finish (“You did have that extra year at Stanford”) and suggested that I visit Murray Jarvik, professor of Pharmacology at the Albert Einstein Medical School, as a possible postdoctoral opportunity. I did, and Murray offered me a place in his lab funded by an Interdisciplinary Fellowship program. So, in 1968, after completing my doctorate under Schiller, I relocated to New York City and Einstein, where Murray told me I should work on whatever I liked.

Einstein

I began at Einstein with studies that continued my thesis topic, but in my first year I had the good fortune to meet Samuel Barondes, associate professor in the Department of Psychiatry. Sam’s lab was conducting in mice some of the first behavioral studies showing the importance of brain protein synthesis for the formation of long-term memory. The work involved inhibitors of protein synthesis, such as cycloheximide and anisomycin, and behavioral tests of memory. Sam was a master of efficiency who aimed at the heart of questions with simple experiments. I saw this work as getting at the nature of memory more directly than what I could do with my cholinergic drugs. After a few conversations, we began to collaborate. The experiments in Murray’s lab continued, eventually yielding three publications, but my enthusiasm had been redirected. The initial efforts with Sam resulted in one paper in Nature and another in Science (Squire and Barondes, 1970; Segal et al., 1971). Sam’s talent for formulating questions and presenting a coherent story was on grand display. In our study of actinomycin-D, an inhibitor of RNA synthesis, the behavioral experiments ran afoul of the toxic effects of the drug. After several efforts, I came to his office with news of the final failure, expecting some mutual commiseration and an abandonment of the project. I knew that we would not be able to say anything compelling about RNA synthesis and memory. Sam said, “Let’s run another group so we can make a different point [memory changes with time] and send it to Nature.”

In the midst of all this, Sam was recruited to the new Department of Psychiatry at the University of California San Diego (UCSD) and invited me to join him. I was familiar with the area because my maternal grandparents had earlier retired to La Jolla for a number of years, and my family had made several cross-country automobile trips to visit them during the late 1940s and early 1950s. So, in 1970, I made the easy decision to move, taking a research scientist position in Sam’s group.

Arriving at UCSD

Collaborative studies with inhibitors of protein synthesis continued with Sam at UCSD and resulted in six publications that described the behavioral actions of the drugs and ruled out various side effects. Even after I obtained an independent position in 1973 (supported by the Veterans Affairs Medical Center) and began working with humans, I did some additional work with the inhibitors, publishing eight papers. Yet one could see that, although much had been learned, this particular approach (drugs and behavior) could take us only so far with the tools available at the time. Moreover, concerns about side effects continued to appear in the literature, despite our efforts to address a number of them directly (Squire et al., 1974; Squire et al., 1976b). With the idea that the story was nevertheless on pretty strong footing, Hasker Davis (a former undergraduate in the lab) prepared a review with me to summarize the case for the importance of brain protein synthesis, during or shortly after training, in the formation of long-term memory (Davis and Squire, 1984). I have always been glad, as Sam and I turned to other topics, that there was an opportunity to do a thorough accounting of where the problem stood at that point. The paper has accumulated more than 1,600 citations. Many years later, an excellent review made the case again, and more comprehensively, revisiting the matter of side effects and drawing on evidence from newer methods for disrupting protein synthesis (Alberini, 2008, Neurobiology of Learning and Memory, 89, 234–246).

The Move to Studying Memory in Humans

What propelled me to human work was a 1971 publication on retrograde amnesia in a mixed group of five memory-impaired patients (Sanders and Warrington, 1971, Brain, 94, 661–668). Retrograde amnesia refers to memory loss for information that was acquired before the onset of memory impairment. The patients in that study had memory loss (for past news events and famous faces) that extended into the past across the three to four decades that were measured, and its severity was similar at all past time periods. This result completely perplexed me. It did not fit with what I had come to understand from the animal literature, in which retrograde amnesia was typically brief and also temporally graded, affecting recent memory more than older memory. Retrograde amnesia in animals was thought to provide evidence for memory consolidation: the idea that memory is initially in a labile state but becomes fixed and less vulnerable to disruption as time passes after learning.

At the time, there was active interest in how long it takes after learning for this fixation process to occur. The animal work suggested a time frame of seconds, minutes, or hours, perhaps reflecting the transition from a fragile short-term memory to a stable long-term memory. I also had been intrigued by a few clinical reports that patients can sometimes exhibit retrograde amnesia extending back a few years. However, the evidence for such prolonged, but still temporally graded, memory loss was weak, and the idea did not attract much attention. When an interview about the past covers a period of years, questions about the remote past tend to query salient events that have proved resistant to forgetting, whereas questions about the recent past query less salient events that may be soon forgotten (in the extreme, “What was the name of your first school?” vs. “What did you have for breakfast today?”). As a result, when a patient appears to have lost mainly recent memory, one cannot know whether the patient really has temporally graded memory loss for the past or whether the patient simply has lost the weaker memories.

The First Experiments: Memory Consolidation

I began by asking if long gradients of retrograde amnesia covering a year or more can actually occur. What was needed, I thought, was a method to sample past events equivalently—that is, a method to assess information from past time periods that had initially been learned to the same extent. After six months of trial and error, we developed a memory test for the names of television programs that had broadcast for a single season, 1957–1972 (Squire and Slater, 1975). The correct answers (five items/year) were the names of one-season programs, and each program was presented together with three fabricated titles. Popular exposure to the programs across time periods was quite similar, based on data from the Nielsen Company for percent of households having a television, percent time watching television, and individual ratings for each program. Moreover, program names were apparently learned close to the time the programs were on the air, because high-school students failed to recognize the names of programs broadcast when they were very young, and adults residing outside the United States for a period of years were poor on questions about programs broadcast while they were away.

Being in a Psychiatry Department, I was aware that a number of facilities in the area offered electroconvulsive therapy (ECT) as a treatment for depressive illness. ECT seemed to provide a perfect way to study the temporal dimension of retrograde memory loss. Indeed, electroconvulsive shock, or ECS as it was called, was at the time the most widely used method for studying retrograde memory in rodents. We gave half the test to patients a day before their first treatment and the other half 1 hour after the fifth treatment at a time when memory impairment is readily detected. The results were straightforward. Before ECT, recently broadcast programs were remembered better than programs broadcast many years ago (evidence for normal forgetting). After ECT, memories acquired up to three years before treatment were markedly impaired, but more remote memories (4 to 17 years old) were fully spared (Squire et al., 1975). Moreover, the performance score after ECT for the most recent few years was not just low but lower than the scores for any of the more remote time periods. This particular result, that recent memory was even poorer after ECT than more remote memory, was the key feature of the data that made the findings relevant to memory consolidation (see Squire, 1992, for elaboration of this point). In subsequent work, we found a similar pattern of memory loss when we asked about the temporal order in which the programs had broadcast (Squire et al., 1976a) or asked patients to recall details about the programs (Squire and Cohen, 1979).

These findings provided the first evidence that resistance of memory to disruption can increase over a lengthy time period (a few years). Thus, the same kind of experiment that in animals had suggested a brief period of consolidation, and a rapid transition from a labile to a stable state, now suggested that consolidation depended on reorganization within long-term memory itself. The process proceeds such that the same material that is becoming harder to recall (through normal forgetting) is also becoming less vulnerable to disruption.

I wondered why these findings in humans were so different from the finding of very brief retrograde amnesias in rodents. So a few years later, we did a large study with ECS in mice (Squire and Spanis, 1984), giving ECS four times at 1-hour intervals to mimic the multiple treatments in humans that had yielded a few years of retrograde amnesia. We gave ECS at one of seven different delays (1–70 days) after training on a one-trial task, and tested retention two weeks after treatment. Control animals exhibited gradual forgetting with increasing retention intervals. ECS caused extended retrograde amnesia covering the period one day to three weeks prior to treatment. Memories acquired three to ten weeks before treatment were fully spared. These findings increased by an order of magnitude the time period across which temporally graded retrograde amnesia had been demonstrated in rodents, presumably as a result of using a strong amnestic protocol. The results showed that in mice, as in humans, the process during which memory becomes less vulnerable occurs within long-term memory. Perhaps it was a coincidence, but we also noticed that the percentage of life span covered by these longer retrograde amnesias was similar in the two species.

Clinical and Practical Studies of ECT

When I was studying ECT in the 1970s, I discovered that a number of practical questions about how a course of ECT affects memory had not been addressed as thoroughly as they might. How long after ECT does memory impairment last? Are any effects permanent? How do patients rate their memory abilities as time passes after treatment? We were well equipped to pursue these questions. Moreover, this was the kind of thing that the psychiatrists who were giving us access to their patients really wanted to know. The first study simply compared the new learning ability of 38 patients who, six to nine months earlier, had had a course of bilateral ECT (mean = 10 treatments), right unilateral ECT (mean = 9 treatments), or hospitalization without ECT (Squire and Chace, 1975). Fifteen inpatients currently receiving bilateral ECT were also tested during their course of treatment to provide a profile of memory impairment against which follow-up performance could be compared. On six tests of recall and recognition (both verbal and nonverbal), the inpatients currently receiving bilateral ECT were markedly impaired, but the two follow-up groups tested six to nine months after ECT performed virtually the same as the inpatients who had never received ECT. The tests were sensitive enough to detect the weakening of memory that occurs from one decade to the next during normal aging. Interestingly, and despite their good performance, 10 of the 16 patients in the bilateral group expressed persistent complaints about their memory abilities. In other tests of new learning, bilateral ECT always disrupted memory more than right unilateral ECT (Squire, 1977).

In a different study, we assessed retrograde memory loss by giving four tests involving public events or personal memories on three occasions: before bilateral ECT, one day to one week after the completion of treatment, and about seven months later (Squire et al., 1981). ECT initially disrupted past memories as measured by all the tests. As time passed, the retrograde amnesia shrunk, as had been described in the clinical literature, for example, after head trauma. By seven months after ECT, recovery was nearly complete with the exception of persistent memory loss from the period several days to possibly a few weeks before treatment. We later demonstrated shrinkage of retrograde amnesia with formal tests in other kinds of transient amnesia—after ECS in mice (Spanis and Squire, 1987) and after TGA (transient global amnesia) in patients (Kritchevsky and Squire, 1989). In the case of TGA, we estimated the permanent retrograde loss to cover several hours to days; in the case of mice and ECS, we estimated one to five days.

Some insight into what explained patients’ persistent memory complaints, despite all the evidence of recovery, came when we constructed tests to get at this quantitatively (Squire et al., 1979; Squire and Slater, 1983). For example, we presented a horizontal bar marked into time bins, including “now” and “time of ECT,” and asked patients to indicate what time periods they had difficulty remembering. Although there was considerable variability, 31 patients who had received bilateral ECT three years earlier indicated a median of two months of anterograde amnesia and six months of retrograde amnesia. What was interesting about this was that the patient descriptions, on average, resembled what we had measured with our objective memory tests. In the case of retrograde memory, we had identified some persistent loss of the past from the period just before treatment. In the case of anterograde amnesia, the capacity for new learning did improve and gradually recovered during the weeks and months after treatment. However, memory for the period shortly after ECT, when new learning was affected, did not return, presumably because these memories had not been established in the first place. I also proposed an additional factor that I thought might contribute to complaints about memory. As time passes after treatment, and memory improves, it may become increasingly difficult to discriminate the ordinary lapses and failures of memory that are part of daily life from failures attributable to ECT.

As a result of our ECT work, I was invited to participate in a number of panels and symposia, including a Task Force on ECT (1975–1978) organized by the American Psychiatric Association. In these formats, I was usually the lone representative of the “costs” of ECT in the context of broader discussion of safety and efficacy. Often, I found myself somewhere between the treating psychiatrists, who hoped for as little memory impairment as possible, and patient advocates, who thought that blaming any part of memory complaints on ordinary lapses in memory rather than on ECT was tantamount to saying, “It’s all in your heads.” I remember speaking at a National Institute of Mental Health (NIMH) Consensus Conference in 1978, which was open to both academics and lay people, where I had the unique experience of hearing a hiss from the audience as I discussed the thorny issue of memory complaints.

Bringing in Neuroanatomy

With the development of modern imaging techniques, especially structural magnetic resonance imaging (MRI), it became possible to bring neuroanatomy to our studies, including the study of the long consolidation process that had been revealed by ECT and ECS. I had always believed that neuroanatomy was critical for studies of memory-impaired patients so as to relate patient work to animal work, and for moving the whole enterprise in the general direction of biology. We began these efforts with Gary Press, then a neuroradiologist at UCSD, and David Amaral, a fine neuroanatomist who was then at the Salk Institute. The first success was a high-resolution protocol for imaging the human hippocampus, which we accomplished by obtaining images precisely perpendicular to its long axis (Press et al., 1989). None of us had ever seen the human hippocampus with such clarity in a living person, and I don’t believe anyone had. I guess Nature thought so, too, as they put a coronal image on its cover showing a beautiful left and right hippocampus belonging to one of my graduate students. Seeing the first images appear on the monitor was one of those exhilarating scientific moments that one remembers forever. This development meant that we could now identify (and measure) volume loss in patients whose memory impairment resulted from hippocampal damage (or larger medial temporal lobe damage) and also could distinguish these patients from patients with diencephalic amnesia, such as Korsakoff syndrome (Squire et al., 1990).

During the same time period, we had begun to assemble a small population of memory-impaired patients with selective hippocampal lesions whom we could characterize with these methods. This meant we could move to studying memory in these patients instead of in patients receiving ECT. Our first studies of retrograde amnesia with this group found temporally limited retrograde amnesia (for past news events and famous faces), but the questions we had constructed were grouped by decade and did not have good temporal resolution (Squire et al., 1989; Reed and Squire, 1998). We could not use the television test because viewing statistics had become less stable from year to year, as television moved from broadcasting on only three channels to broadcasting on multiple channels.

Instead, graduate student Joe Manns put together several hundred questions that asked participants about notable news events that had occurred in a particular year from 1950 to early 2002 (Manns et al., 2003). Testing proceeded in a free-recall format, and the data for each patient were analyzed according to the year the patient developed memory impairment. In this way, a score for each patient was calculated for the period of anterograde amnesia and, in five-year intervals, for the period of retrograde amnesia up to a maximum of 30 years (mean = 32 questions for each time period). On this test, the patients with damage thought to be limited to the hippocampus were impaired at recalling events that had occurred after the onset of their amnesia and for the period one to five years before amnesia. Memory for more remote events was intact. Christine Smith joined the lab as a postdoc at about this time (and stayed on to become an invaluable colleague and leader of many projects, eventually with her own faculty position). Using the same news-event questions and fMRI, Christine found gradually decreasing activity in the hippocampus as participants recollected events from 1 to 12 years ago and a constant level of activity during recall of more remote events from 12 years up to 30 years ago (Smith and Squire, 2009).

These findings supported our developing idea that the hippocampus has a time-limited role in the formation of memory (Squire, 1986, 1992; Squire and Alvarez, 1995), an account that is sometimes referred to as the standard model of memory consolidation. After learning, the hippocampus initially works together with distributed sites of memory storage in neocortex, but as time passes, the role of the hippocampus gradually diminishes and a more permanent memory is established in the neocortex. The idea is not that memory literally transfers to the neocortex, for information is encoded in neocortex as well as in hippocampus at the time of learning. The idea is that gradual changes in neocortex increase connectivity among the cortical regions that ultimately store the learned material. These changes eventually allow the neocortex to support recall on its own without the participation of the hippocampus. To make the basic point more concrete, we constructed a simple network model that behaved in a way that was consistent with the data (Alvarez and Squire, 1994).

There was initially skepticism about the idea that such a process could continue for years, although I did point out that forgetting itself can proceed over even longer time periods (Squire, 1989). Later, we began to study the matter prospectively in animals with hippocampal lesions and found long gradients of retrograde amnesia, just as we had found earlier with mice given ECS. In rats, the gradient extended across 30 days (Clark et al., 2002a); in monkeys, eight weeks (Zola-Morgan and Squire, 1990). The monkey study was especially satisfying because it was one of the first such studies and was the only study on this problem ever done in monkeys. It required scheduling multiple events across the calendar, all in advance of an outcome that we would not see for several months. Monkeys learned 100 simple object discriminations beginning 16, 12, 8, 4, and 2 weeks before surgery (20 object pairs per time period). After surgery, we assessed the status of object memory by presenting each of the 100 object pairs for a single choice trial.

Following the monkey work, a number of groups in the 1990s found long gradients of retrograde amnesia after hippocampal lesions in mice, rats, and rabbits. It is now widely appreciated that, in rodents, the time needed for memory to become independent of the hippocampus is about 30 days. In our monkey study, it was eight weeks, and in humans it was a few years. I have supposed that the process develops more slowly as one moves from simple to more complex nervous systems. In any case, we knew now that memory consolidation, as studied in our own work on retrograde amnesia, was never about a transition from a short-term (labile) to a long-term (stable) memory but described a gradual process during which memory becomes independent of the hippocampus and is consolidated in neocortex. This process is now often referred to as systems consolidation to distinguish it from the cellular-level (consolidation) process that depends first on changes in synaptic strength and then on protein synthesis and morphological change. An excellent review summarized where things stood with systems consolidation at that point (Frankland and Bontempi, 2005, Nature Reviews Neuroscience, 6, 119–130). Ten years later, in collaboration with Richard Morris and others, we wrote a review as well (Squire et al., 2015).

It turned out that about 30 years following the 1971 publication in Brain that had brought me to the study of human memory, I could understand their report of an ungraded retrograde amnesia that extended decades into the past. It’s all in the anatomy. First, none of the patients in the 1971 study had the restricted, bilateral hippocampal damage that we had found to result in only a few years of retrograde amnesia. One of these early patients proved to have left lateral hippocampal damage together with a right temporal lobectomy that left intact only part of the right superior temporal gyrus. Another had had coal gas poisoning, and three had Korsakoff syndrome, a form of diencephalic amnesia. Second, extended retrograde amnesia across decades can occur when the lesions extend beyond the hippocampus into the adjacent structures of the medial temporal lobe as in patients E. P. and G. P. (Reed and Squire, 1998; Bayley et al., 2006). In these cases, retrograde amnesia covered as much as 30–50 years (but with substantial sparing of very remote memories from adolescence and young adulthood). Third, retrograde memory loss can extend even into childhood when the pathology involves most of the medial and also lateral temporal lobe bilaterally (patient G. T.), or the medial temporal lobe plus areas of temporal and frontal neocortex (patients H. C. and P. H.) (Reed and Squire, 1998; Bayley et al., 2005b). Indeed, unlike any other patients we have studied, G. T. and P. H. were unable to recall a single autobiographical memory from early life, perhaps because their cortical damage directly disrupted sites of long-term memory storage. This all added up to the simple idea that there is not a single phenotype of retrograde amnesia or a single “amnesic syndrome” but rather different phenotypes of retrograde amnesia and different presentations of memory impairment, all dependent on neuropathology.

Other reports of impaired autobiographical recall from childhood often have included the suggestion that hippocampal damage itself is responsible. The proposal is that autobiographical information (but not factual information) depends on the hippocampus for as long as a memory persists. I have been sour about this idea and have not found compelling evidence for it. To be incapable of any autobiographical remembering takes a lot more than hippocampal damage. Such an impairment requires a patient such as G. T., with his large medial and lateral temporal lobe lesions, or the head trauma patient K. C., with his medial temporal lobe lesion and widespread neocortical damage, who was well described by investigators in Toronto (Tulving et al., 1988, Brain and Cognition, 8, 3–20).

Our own three studies of autobiographical memory found intact recollection of remote autobiographical memories after hippocampal lesions, even after large medial temporal lobe lesions, together with impaired recollection of recent memories (Bayley et al., 2003; Kirwan et al., 2008a; Dede et al., 2016a). We tried to sort all this out in a review (Squire and Bayley, 2007), and I continue to believe that the clearest perspective will come from neuroanatomy and from careful description of the locus and extent of lesions. One also recognizes that the topic of autobiographical recollection itself is particularly challenging, because the available testing methods are a little “soft,” and it’s unclear how to study the problem in experimental animals.

The best kind of anatomical information, of course, comes from postmortem histological analysis of patients who have been well studied during life. Succeeding at this is difficult and rarely accomplished, as it depends on cooperation from many directions, especially on being able to obtain the brain within hours of death. Nevertheless, we have been pretty dedicated in these efforts, and my group, in collaboration with David Amaral, has been able to present eight cases (Zola-Morgan et al., 1986; Rempel-Clower et al., 1996; Gold and Squire, 2006; Insausti et al., 2013).

An example of the benefits of postmortem data came when Ricardo Insausti and David Amaral carried out a detailed neurohistological analysis for patient E. P., whom we had studied for 14 years (Stefanacci et al., 2000; Insausti et al., 2013). E. P. had developed profound memory impairment after encephalitis, an impairment that proved to be even more severe than in the noted patient H. M. (Scoville and Milner, 1957, Journal of Neurology, Neurosurgery, and Psychiatry, 20, 11–21; Squire, 2009). We had studied E. P.’s MRI images, obtained 8 and 12 years earlier, and had noted shrinkage of the lateral temporal lobe. Yet, I was still impressed by the extent to which his entire temporal lobe bilaterally was shrunken and atrophic, probably (as we thought about it) because of loss of afferent input (e.g., from amygdala and perirhinal cortex) as well as intracortical afferents that funnel through the temporal stem. Loss of afferents from lateral temporal cortex through retrograde degeneration also could have been a factor. It seemed likely to us that some shrinkage within lateral temporal cortex may be a typical (albeit indirect) consequence of large medial temporal lobe lesions, given the substantial connectivity between the medial and lateral temporal lobe. In addition, it is possible that shrinkage within the lateral temporal lobe increased over the years as anterograde and retrograde degeneration progressed. This scenario raised the possibility that the considerable extent of E. P.’s retrograde memory loss, as described earlier (Reed and Squire, 1998; Bayley et al., 2006), could have reflected, at least in part, these changes in his lateral temporal cortex. This means that it is important to evaluate the status of lateral temporal cortex, and the possible contribution of lateral temporal damage, when evaluating patients with large medial temporal lobe lesions. It is also a good idea to obtain MRI data close to the time that neuropsychological and neurohistological data are obtained.

Nonhuman Primates

In 1978, another publication appeared that dramatically altered the course of my work (Horel, 1978, Brain, 101, 403–435). Horel proposed that it was not hippocampal damage that impairs memory but damage to temporal stem white matter, which lies just above the hippocampus and connects lateral temporal neocortex to diencephalic and other subcortical targets. The temporal stem, he argued, would necessarily have been damaged by the surgical approach that had been used to resect medial temporal lobe structures in monkeys and in humans, including patient H. M. Horel noted, too, that efforts in rats and monkeys with hippocampal lesions to establish an animal model of H. M.’s condition had foundered up to that point. I had to admit that the case for the hippocampus was not as rock solid as I had thought. I was so eager to jump into the problem that I asked a young graduate student at UCSD if he would like to do a monkey project with me, a ludicrous idea as I knew nothing about monkey work except from reading (he declined). I began making serious inquiries and had the good fortune to hear from Stuart Zola-Morgan (later Stuart Zola), who was just completing postdoctoral work with Helen Mahut in her Boston primate lab and happened to find my letter to Helen, which was sitting neglected on her desk. Stuart came to UCSD, set up a monkey lab, and eventually obtained an independent faculty position. Working with Stuart was one of the great pleasures of my career. It involved almost nightly phone calls to talk through the work and continued for 21 years until he left to become director of the Yerkes National Primate Research Center at Emory University.

In an odd coincidence, in the same year that Horel presented his new idea (1978), Mort Mishkin described a profound memory impairment in monkeys with large medial temporal lobe lesions, designed to reproduce H. M.’s lesion and using a task, delayed nonmatching to sample (DNMS), that tested memory for single events (Mishkin, 1978, Nature, 273, 297–298). In DNMS, the monkey first displaces a single (sample) object to obtain a reward. Then after a variable delay, from a few seconds to many minutes, the monkey sees the old object together with a new one and receives a reward for choosing the new one. New pairs of objects are used on each trial. The lesion damaged the hippocampus, the amygdala, and adjacent cortex and came to be identified as the H⁺A⁺ lesion (the plus signs denote that cortex was damaged by the direct surgical approach used to access the hippocampus and amygdala).

This important finding described the kind of memory impairment that one saw in patients and made it possible to ask: What damage within the large territory of this lesion was responsible for the memory impairment? Or, in the light of Horel’s novel suggestion, was damage to the white matter of the temporal stem responsible? Our first study, in which Mort joined, simply compared the effects on memory of temporal stem lesions and H⁺A⁺ lesions (Zola-Morgan et al., 1982). Temporal stem lesions had no effect on DNMS, although they did impair the learning of visual pattern discrimination tasks in which the animal learns which of two patterns is correct (e.g., o vs. +). The H⁺A⁺ lesion severely impaired DNMS but spared pattern discrimination learning. The same H⁺A⁺ monkeys also failed a number of memory tasks in addition to DNMS that patients with medial temporal lobe lesions had failed (Zola-Morgan and Squire, 1985).

We had some ideas about why visual pattern discrimination learning might be spared. Monkeys took as many as 300 trials to gradually learn these two-dimensional pattern tasks, reminding us of the gradual learning of motor-skill tasks and perceptual-skill tasks, which were known by that time to be spared in patients (see the section “Multiple Memory Systems”). In fact, the same monkeys with H⁺A⁺ lesions who had succeeded at difficult pattern discrimination learning also succeeded at learning motor-skill tasks (Zola-Morgan and Squire, 1984). In contrast, these monkeys were impaired on easy discrimination problems involving distinct, three-dimensional objects that could be learned in only 10 trials. Perhaps learning the easy problems was more like learning a fact than acquiring a skill. The monkeys with temporal stem lesions who had failed difficult pattern discrimination tasks were intact at the easy problems (Zola-Morgan and Squire, 1984). Stuart and I wrote a review during this period, developing the idea that difficult pattern discrimination learning tasks in the monkey were largely skill-like tasks, an idea first suggested by Sue Iversen (International Review of Neurobiology, 1976, 19, 1–49), and making the case for a correspondence between the findings for human and nonhuman primates (Squire and Zola-Morgan, 1983). We argued that the effects of temporal stem damage on pattern discrimination learning reflected visual processing deficits associated with the loss of afferents and efferents of the unimodal visual area TE in lateral temporal neocortex.

None of us had paid much attention to the fact that the surgical approach used in these studies to target the hippocampus and amygdala proceeded directly through one or more structures of the adjacent parahippocampal gyrus: perirhinal cortex, entorhinal cortex, or parahippocampal cortex (area TH-TF). Indeed, what I am here calling the H⁺A⁺ lesion was originally termed the A+H lesion, and the plus-sign superscripts were not introduced until several years later (Squire and Zola-Morgan, 1988). The perirhinal cortex, in particular, was barely on the radar, as our graduate student Wendy Suzuki and David Amaral only recently had redefined its borders. Instead of comprising a small area on the lateral bank of the rhinal sulcus, as originally thought, the perirhinal cortex now extended laterally all the way to the medial bank of the anterior middle temporal sulcus in the ventral temporal lobe. These structures of the parahippocampal gyrus would soon prove to be an important part of the story.

At about this time, as our program of human work continued, we had the opportunity to study a patient who became moderately amnesic following an ischemic event in 1978 and was then tested extensively until his death in 1983 (patient R. B.). With the consent of family, we were able to obtain the brain at the time of death, and David Amaral then undertook a detailed histological examination, which revealed a bilateral lesion restricted to the entire rostro-caudal extent of the CA1 field of the hippocampus (Zola-Morgan et al., 1986). This was the first reported case of memory impairment following a lesion limited to the hippocampus in which extensive neuropsychological and neuropathological analysis had been carried out. Here was conclusive evidence that the hippocampus itself was important for memory. In addition, because R. B. was not nearly so impaired as patient H. M., the findings clearly indicated that other areas beyond CA1, most likely outside the hippocampus, must also be important for memory functions. Later, we developed a technique for the monkey that combined stereotaxic surgery with MRI to make substantial lesions of the hippocampus (the H lesion) with little or no damage to adjacent cortex (Alvarez-Royo et al., 1991). These monkeys were moderately impaired on two tasks of recognition memory: DNMS and visual paired-comparison, and (just as R. B. was much less impaired than H. M.) the H monkeys were much less impaired than monkeys with the large H⁺A⁺ lesion (Alvarez et al., 1995; Zola et al., 2000).

Buoyed by the R. B. case, we next prepared an H⁺ lesion in the monkey involving the posterior medial temporal lobe (Zola-Morgan and Squire, 1986). The H⁺ lesion was limited to the hippocampus and the underlying posterior entorhinal and parahippocampal cortices, and it unequivocally impaired memory. Comparisons carried out later between the H⁺ monkeys and the just-mentioned H monkeys indicated that the H⁺ monkeys were more impaired, thus implicating a role for the underlying cortex. Importantly, the fact that the H⁺ lesion nevertheless impaired memory less severely than the H⁺A⁺ lesion meant that anterior structures comprising the A⁺ component of the large lesion must also be important.

The first clue about these anterior structures came from monkeys with stereotaxic lesions limited to the amygdala that spared surrounding cortex (Zola-Morgan et al., 1989a). These monkeys were fully intact on four memory tasks. Moreover, when the H⁺ lesion was made conjointly with A lesions (the H⁺A lesion), H⁺A monkeys were impaired on the same four tasks but no more so than after H⁺ lesions. These findings ruled out the amygdala and turned our attention to what else had been damaged when the amygdala was removed by the conventional surgical approach (the ⁺ component of the A⁺ lesion).

As we began to consider what tissue subjacent to the amygdala might explain the considerable difference in the behavioral effects of H⁺ lesions and H⁺A⁺ lesions, we realized that we didn’t really understand the anatomy of the anterior medial temporal lobe. On a memorable Saturday evening (March 14, 1987), in one of our regular nightly phone calls, Stuart and I decided to cancel the surgery we had scheduled for the following Monday. Then on Monday, we took the brain sections from our earlier studies of H⁺A⁺ lesions over to David Amaral at the Salk Institute. He examined each of the slides and then said, “All these lesions have damage to perirhinal cortex.” I remember throwing up my hands, saying, “That’s it!”

Anatomical studies from David Amaral and his colleagues, published in the same year as our critical conversation with him, had indicated that the perirhinal cortex and the closely associated, and more posterior, parahippocampal cortex provide two-thirds of the cortical input to the entorhinal cortex. Given that the entorhinal cortex originates the major input to hippocampus, these two cortical regions thus provide the principal route by which information from the neocortex reaches the hippocampus. We therefore evaluated the severity of memory impairment in monkeys with lesions designed by David that were limited to the perirhinal cortex and parahippocampal cortex (the PRPH lesion) (Zola-Morgan et al., 1989b). The monkeys with PRPH lesions were severely impaired on three memory tasks, including DNMS, and overall, they were as impaired or more impaired than monkeys with the original H⁺A⁺ lesions. A later study of PRPH lesions showed the same severe deficit on the DNMS task in the tactual modality (Suzuki et al., 1993). Still later, lesions to perirhinal cortex itself, prepared by David, produced a modest, multimodal deficit on the DNMS task, as well as on two other memory tasks (Buffalo et al., 1999). Lesions of the immediately adjacent area TE, a major source of afferents to the perirhinal cortex, had entirely different effects that suggested a visual processing deficit, not a memory impairment.

With the results of the PRPH lesion in hand, we were ready to suppose that, if an H⁺A lesion did not increase the impairment associated with an H⁺ lesion, then an H⁺⁺ lesion should be effective, probably by virtue of damage to perirhinal cortex. We therefore prepared an H⁺ lesion and brought it forward to include the cortex beneath the amygdala that typically had been included in the original H⁺A⁺ lesion. The H⁺⁺ lesion severely impaired memory and approximated the effect of the large H⁺A⁺ lesion (Zola-Morgan et al., 1993). Quantitative measurement indicated that the perirhinal cortex was the only structure that was damaged more extensively in the H⁺⁺ lesion than in the H⁺ lesion.

Now we thought we had it, so we put together a paper identifying (announcing) the anatomical components of the medial temporal lobe memory system: the hippocampus, entorhinal cortex, and the adjacent, anatomically related perirhinal and parahippocampal cortices (Squire and Zola-Morgan, 1991). The amygdala, we wrote, is not a component of this system and has quite distinct functions (e.g., see Zola-Morgan et al., 1991). We emphasized further that this cortex along the parahippocampal gyrus is not simply a conduit for connecting neocortex to hippocampus. Both the H⁺⁺ lesion and the PRPH lesion impaired memory much more severely than the H or H⁺ lesion. Accordingly, the cortex damaged in the H⁺⁺ and the PRPH lesions must be important for memory function on its own. Apparently, information from neocortex can reach the parahippocampal gyrus for some memory storage to occur and need not reach the hippocampus itself. We did not intend to imply that the structures of the medial temporal lobe therefore work together as a single and uniform functional unit, although this view sometimes has been attributed to us.

The monkey project, and the charting of the medial temporal lobe memory system, was one of the most satisfying pieces of work in my career, in no small part because of the pleasure of working with Stuart. It took a long time, but we knew the problem was solvable. Sustained collaboration between peers (we were only three years apart in age) is not so common in science, but it has many useful features. Everything is talked through so that it is hard to fool yourself. The thinking is out loud, as it were, and errors of logic, memory, interpretation, or emphasis are readily exposed.

Bringing in the Rats

Lesion-behavior studies in the monkey come with a number of challenges. Each animal is typically studied for one or two years with multiple tasks, and experiments must be carefully planned. Waste and inefficiency carry a high cost. Furthermore, studies requiring many animals, extended pilot work, or the charting of parametric effects are often out of bounds. So, in 1998, Stuart and I had discussions with Bob Clark, a postdoctoral fellow in our group, about the prospects of setting up a rat lab. The idea was to develop a program that would complement the monkey work and allow us to pursue related questions. I had tended to view what I was studying as essentially mammalian, so it seemed reasonable to me that what we could learn from rats would be relevant to what we had been learning from monkeys and humans. Bob enthusiastically took this on, eventually obtained an independent faculty position, and collaborated with us (and then with me after Stuart left) on a number of useful studies until we retired the rat program in 2018.

As an example, it was well established in humans that immediate memory (the limited amount of information that can be held in mind such as a short string of digits), is intact after medial temporal lobe lesions and distinct from long-term memory, which is impaired. However, during the period that the animal model of human amnesia was being developed in the monkey, it was a matter of some debate whether the same distinction could be demonstrated in experimental animals. There was doubt if experimental animals even had an immediate (or short-term) memory and, if they did, perhaps it was organized differently than in humans.

In our study (Clark et al., 2001b), rats with hippocampal lesions first learned the DNMS task at a normal rate when the delay between the sample presentation and the choice was only 4 seconds. When the delay was then increased to 1 or 2 minutes, performance was impaired. Furthermore, during delayed testing, performance was intact when 4-second delay trials were introduced intermittently, indicating that both the nonmatching rule and short-term memory remained available. Most important, even when extended testing was given at a 1-minute delay, exceeding the training and testing that had been given at the 4-second delay, performance remained intact at the short delay and impaired at the long delay. This result demonstrated in the rat the same hippocampus-independent short-term memory and hippocampus-dependent long-term memory that we were familiar with in memory-impaired patients. Whether rats are actually holding short-term memory “in mind” is a different question.

Nicola Broadbent and Bob Clark also undertook a large study involving nearly 150 rats that helped explain why impaired performance on spatial memory tasks has been so easy to demonstrate after hippocampal lesions, and impaired recognition memory has often been difficult to demonstrate (Broadbent et al., 2004). Spatial memory deficits in the water maze were obtained after dorsal hippocampal lesions that encompassed only 30–50% of the total hippocampal volume, whereas object recognition was impaired only when the lesions encompassed 75–100% of the hippocampal volume. It appeared that spatial memory performance requires more hippocampal tissue than does recognition memory. Small hippocampal lesions that reliably impair spatial memory can spare recognition memory. Inasmuch as the water maze task is effectively a test of recall, I expect that one might find the same thing with any recall task, regardless of whether or not the task is spatial.

Another interesting issue emerged in the late 1990s when several animal studies suggested that the perirhinal cortex might be important not only for memory but also for visual perception, especially for discriminating between stimuli with high feature overlap. We carried out studies in patients, finding no evidence for this new view (Shrager et al., 2006; Kim et al., 2011; Knutson et al., 2013) but also wanted to construct a strong test of the idea in the rat. Using a two-choice discrimination task developed by Pamela Reinagel at UCSD, we first gave rats extensive training to discriminate between two pictures (paintbrush vs. flashlight). Rats then maintained memory performance at a high level while interpolated probe trials tested their perceptual ability (Clark et al., 2011). The probe trials varied the similarity between the two stimuli across 14 difficulty levels by gradually morphing one stimulus into the other. The 14 different probe trials yielded performance scores from 87% correct to chance (50% correct), and animals with perirhinal lesions and control animals obtained virtually identical scores at every difficulty level. Overall, we never found support for a role of perirhinal cortex in perception. We suggested, with others, that tests of this idea in animals tended to confound perception and memory because the tests used to assess perception typically require learning.

Lastly, we carried out a number of studies trying to understand why the temporal gradients of retrograde amnesia so commonly found in humans and animals, including in our rats (Clark et al., 2002a), had never been found in the water maze task. We made only a little progress on this problem, finding impaired (rather than spared) remote memory on three different versions of the water maze task, using training-surgery intervals as long as 14 weeks (Clark et al., 2005a), giving animals extensive water maze training early in life (Clark et al., 2005b), using reversible lesions (Broadbent et al., 2006), and using beacons to reduce the burden on navigation (Clark et al., 2007). It remains a puzzle to me, though we did offer some speculation about it based on limitations of rat frontal cortex and the performance requirements of the water maze (Clark et al., 2007; Kim et al., 2013b; Sapiurka et al., 2016).

I have supposed that these findings in the water maze are due to particular features of the task and need not imply that hippocampal lesions should generally impair remote spatial memory. First, a few studies by others have demonstrated spared remote memory after hippocampal lesions in other tasks that require some form of spatial memory (e.g., Tse et al., 2007, Science, 316, 76–82). Second, a substantial study led by graduate student Edmond Teng is pertinent to this problem. Our patient E. P., despite his large medial temporal lobe lesions, could recall the spatial layout of the region where he grew up and then left as a young adult more than 50 years earlier (Teng and Squire, 1999). He also did it for PBS TV in the presence of the program’s host, Alan Alda. He could mentally navigate, construct novel routes, and point correctly to landmarks while imagining himself at various locations. E. P. did all this as well as healthy controls who had grown up in the same town and also moved away. Yet he had acquired no knowledge of the neighborhood where he had lived for six years after he became amnesic, and he could not point in the direction of the ocean, two miles away. We thought this was pretty strong evidence for sparing of remote spatial memory after hippocampal damage.

Multiple Memory Systems

Anyone with an interest in memory who lived through the 1960s and 1970s remembers the confusion that abounded as investigators tried to replicate patient H. M.’s memory impairment in rats and monkeys. Animals with lesions similar to H. M.’s 1953 lesion, even monkeys prepared by H. M.’s surgeon, did not exhibit what one would call a memory impairment. It took Mishkin’s demonstration in monkeys of a memory impairment in the DNMS task (in 1978) to show that a viable animal model of H. M. might be within sight. Why it took so long is a fascinating story.

The story begins with Brenda Milner’s discovery in 1962 that H. M., despite the severity and scope of his memory impairment, was capable of learning a hand-eye coordination skill (mirror drawing) over a three-day period, although on each day, he had no memory of having practiced the task before. While this showed that H. M.’s memory impairment was not absolute, discussions for a long time afterward tended to set motor skills aside as an exception, a less cognitive form of memory, with the view that all the rest of memory was of one piece and was impaired in amnesia. Yet, it turned out that motor skills were just the beginning.

My first graduate student, Neal Cohen, and I had the good fortune to find the first hint of what lie beyond motor skills when we considered that certain pattern-analyzing abilities seemed to share some properties with motor skills. We discovered that memory-impaired patients could acquire the perceptual skill of reading mirror-reversed words at a normal rate, despite poor memory for the task and for the words that had been read (Cohen and Squire, 1980). The finding suggested to us a principled distinction between the learning of procedures and the remembering of facts, reminiscent of the philosopher Gilbert Ryle’s 1949 distinction between “knowing how” and “knowing that.” Neal took all this across campus to consult with David Rumelhart, a gifted cognitive scientist, and returned with news of a distinction between declarative and procedural knowledge, which had been introduced recently in the literature of artificial intelligence. The distinction apparently had not gained much traction there, being seen rather as two different, equally useful, ways to represent information. But it seemed exactly right to us as a brain-based distinction describing what we thought to be a fundamental idea about the organization of memory. Our idea was that declarative memory is available as explicit recollection and is impaired in amnesia. Procedural memory is skill-based information embedded in procedures that can be expressed only through performance, that is, by executing the procedures. Procedural memory is spared in amnesia.

We soon found other examples of preserved learning, some of which seemed to move beyond skill learning itself: the ability to resolve stereoscopic images; effects of recent context on perceptual judgments, termed adaptation-level effects (Benzing and Squire, 1989); cognitive skill learning (Squire and Frambach, 1990); text-specific reading skill (Musen et al., 1990); artificial grammar learning (Knowlton et al., 1992); and category learning (Knowlton and Squire, 1993). Still other examples, studied by us and others in the 1980s, came from the phenomenon of priming and from classical conditioning (see later sections), and took us even further beyond skill learning. Indeed, the diversity of phenomena found to be spared in amnesia soon persuaded us to set aside the declarative-procedural terminology in favor of a biological distinction between declarative and nondeclarative memory (Squire and Zola-Morgan, 1988). Declarative memory is dependent on the medial temporal lobe, and nondeclarative memory is an umbrella term referring to multiple kinds of memory supported variously by the neostriatum, amygdala, cerebellum, and neocortex. At about that time, I began using a tree diagram rather than a dichotomy to represent the memory systems of the brain (e.g., Squire, 1986). Endel Tulving also wrote about multiple memory systems during this period from a psychological perspective (1985, American Psychologist, 40, 385–398). What had happened in the early 1980s was the discovery that memory impairment after hippocampal lesions is a much narrower condition than originally thought. Some tasks that had been given to animals with lesions, in efforts to model H. M.’s memory impairment, were tasks that animals could learn nondeclaratively. In other words, the objective of replicating H. M.’s memory impairment in animals was for many years defeated because there was not yet an accurate description of the condition that needed to be modeled.

Another interesting task, different from a skill, is the gradual feedback-guided learning that results in habit learning. Following on work by others in rats and monkeys, which had suggested the importance of the neostriatum (not the hippocampus) for habit learning, we asked whether there was a parallel in humans to this kind of learning. We tested memory-impaired patients and patients with Parkinson’s disease on a probabilistic classification task (the weather task). In this study, led by postdoctoral fellow Barbara Knowlton, participants tried to learn which of two outcomes (rain or sunshine) would occur on each trial (Knowlton et al., 1996). Each of four cues was probabilistically related to the outcome, and on each trial one, two, or three of the cues was presented. The idea was to defeat the strong tendency to memorize cue-response associations (using declarative memory) and to encourage decisions based more on a gut feeling. Memory-impaired patients learned the task but later could not answer questions about the training episode. Patients with Parkinson’s disease failed to learn the task but had intact memory about the training. This double dissociation of lesion and task demonstrated that the brain areas damaged in the two patient groups, the neostriatum (caudate and putamen) and the medial temporal lobe, supported separate and parallel learning systems. The findings further demonstrated that habit learning tasks in humans could be acquired nondeclaratively.

Characteristics of Declarative and Nondeclarative Memory

During this period, we were sometimes asked whether declarative and nondeclarative memory differed in any interesting way other than that declarative memory was impaired by medial temporal lobe lesions and nondeclarative memory was not. One would expect that if the distinction were biologically important, different kinds of memory should have different purposes and different operating characteristics. An insight into this issue came when Paul Reber, a postdoctoral fellow, used transfer tests to assess what participants knew about the weather task after successfully learning it. The transfer tests either created new conditions that required flexible use of task knowledge or simply recreated the conditions of the training task (Reber et al., 1996). Controls exhibited flexible knowledge, but the memory-impaired patients did not. This result suggested that one difference between declarative and nondeclarative memory is the difference between flexibly organized information and rigidly organized, inflexible information.

We encountered a more dramatic example of this when we tried to teach our patient E. P. a series of 48 three-word sentence frames (e.g., MEDICINE cured HICCUPS) during 24 study sessions given over a period of 12 weeks (Bayley and Squire, 2002). E. P. performed much more poorly than controls, but eventually achieved a score of 18.8% correct on retention tests given after 24 sessions (MEDICINE cured ???). Controls scored 49.5% correct after only two study sessions. We had thought that E. P. might simply have some residual ability for acquiring declarative memory. Yet, what E. P. learned was different from what controls learned. What E. P. learned proved to be inflexible and available only when the original training conditions were reinstated. When the middle word of the sentence was replaced by a synonym (e.g., MEDICINE relieved ???), his performance collapsed altogether, and he answered only one question correctly. This same manipulation scarcely affected control performance. It was also striking that E. P. was entirely unaware of the little that he had learned. His confidence ratings were the same for correct and incorrect responses, he did not acknowledge that he was sometimes producing correct answers, and he never gave an indication that the test material was familiar.

Based on this result, together with what we had been finding with priming and classical conditioning (see later sections), we had begun to suppose that awareness of what was learned might be another key feature of declarative memory and that performance on medial temporal lobe-dependent tasks reflects aware (conscious) memory. Conversely, performance on medial temporal lobe-independent tasks reflects unaware (unconscious) memory. This formulation was frequently challenged based on indications that some hippocampus-dependent tasks appeared to be acquired in the absence of awareness. Also, many preferred the idea that the nature of the task, rather than the presence or absence of conscious knowledge, determined whether learning depends on the medial temporal lobe. We looked into all these proposals rather carefully, through experiment, and always found additional support for our original formulation. For example, in tasks of transitive inference, participants were first trained on overlapping pairs of items (e.g., A+ B-, B+ C-, C+ D-, D+ E-, where + and - indicate correct and incorrect choices). Later, participants who chose B over D when presented with B and D were said to demonstrate transitive inference. Christine Smith found that the ability of healthy volunteers to exhibit transitive inference was directly related to their awareness of the hierarchical relationship among the training elements (Smith and Squire, 2005). Patients with hippocampal damage were unaware of the hierarchy and did not exhibit transitive inference.

In other studies, we were able to construct critical tests of the connection between aware learning and hippocampal function when memory was assessed by eye movements. As first shown by Neal Cohen and his colleagues, individuals tend to inspect novel scenes differently than familiar scenes, and they tend to direct their gaze disproportionally toward a region of a scene that has been altered. In our work, led by Christine Smith, we consistently found that the tendency to gaze at the manipulated region of a scene occurred only when individuals were fully aware that a manipulation had occurred (Smith et al., 2006; Smith and Squire, 2008). Memory-impaired patients, overall, did not direct their gaze toward the altered region because they usually did not remember the scenes. But, on a few occasions, when they were aware of the manipulation, they (like controls) gazed at the altered region (Smith and Squire, 2018). We found the same link between conscious memory and medial temporal lobe function when eye movements were recorded as individuals tried to decide which of three scenes they had recently studied (Urgolites et al., 2018).

In another study, we found the other kind of link: an eye movement effect that was independent of conscious knowledge and that was also independent of the medial temporal lobe (Smith and Squire, 2017). Healthy controls explored new and old scenes differently (making fewer fixations and sampling fewer regions when looking at old scenes), but this effect was unrelated to whether they correctly recognized each scene’s new-old status. Moreover, memory-impaired patients exhibited the same differential exploration of new and old scenes as controls. Thus, our data remained consistent with the idea that declarative memory represents flexible, conscious knowledge and is dependent on the medial temporal lobe. When performance is unrelated to and independent of conscious knowledge, as in the latter study, performance is independent of the medial temporal lobe.

The Concurrent Discrimination Task

Perhaps the most compelling demonstration of the characteristics of declarative and nondeclarative memory came from a different direction, when we were forced to reexamine the eight-pair concurrent discrimination task. This task, which had been used for years in work with monkeys, involves learning which object in each of the eight object pairs has been designated “correct.” Typically, 40 trials are presented each day, one pair at a time, such that each pair is encountered five times. For humans, this is a typical declarative memory task. Participants memorize which object is correct in each pair, and they can learn in two or three sessions. Patients with medial temporal lobe lesions were markedly impaired on this task (Squire et al., 1988).

One day in the mid-1990s, our graduate student, Beth Buffalo, came to the lab meeting with the records for all the monkeys in our lab that had ever been tested on the concurrent discrimination task. Normal monkeys learn this task in about 500 trials. Beth told us that monkeys were impaired on the task, not by the medial temporal lobe damage itself, but only when the lesion reached laterally enough to include visual area TE (Buffalo et al., 1998). Subsequently, Ed Teng found an impairment in the concurrent discrimination task when the lesion included the tail of the caudate nucleus (Teng et al., 2000). This was pretty surprising news, because in our big 1983 review, Stuart and I had endorsed the concurrent discrimination task as one of three tasks appropriate for modeling H. M.’s impairment in the monkey. Yet now, with these new findings, and remembering the weather task and the nature of habit learning, we had to suppose that monkeys were likely learning the concurrent discrimination task as a habit. The critical anatomical projection then would be, not from visual area TE to the medial temporal lobe, but from area TE to the caudate nucleus. If so, the implication would be that humans and monkeys were learning the same concurrent discrimination task with different brain systems.

This idea raised a fascinating question. Might patients with profound amnesia, and no apparent capacity for declarative memory, be able to learn the concurrent discrimination task as the monkey learns it, not rapidly as declarative memory but slowly as a habit through gradual trial-and-error learning? If so, would the patients then acquire unconscious knowledge (whatever that might mean for this task) and would this knowledge have different properties than if it had been learned declaratively? We tested two patients with large medial temporal lobe lesions, E. P. and G. P., twice each week by presenting each object pair and asking them to make a choice by picking up one of the objects, turning it over, and discovering whether the word “correct” appeared beneath the object’s base (Bayley et al., 2005a). Controls mastered the task in three sessions. Surprisingly, E. P. and G. P. learned successfully as well, but only gradually during the 36 and 28 sessions, respectively. They eventually reached a score of 95% correct after more than 1,000 trials. Yet, in interviews before each testing session, they never could describe the task, the instructions, or the objects. Even during testing, they never recognized that they had encountered the task before. Comments offered by the patients during the test days were particularly illuminating. When asked after session 34 if he had a strategy, E. P. said, “No. It’s just up here [pointing to head] . . . It seems like it’s up there, and it comes down and out.” When asked during session 23, “Why are you selecting that one?” G. P. said, “It’s just jumping out at me ‘I’m the one.’ I keep wanting to pick it.”

To test if the acquired knowledge were rigidly organized, as we thought it should be in the case of nondeclarative memory, we administered a sorting task a few days after training was complete. All 16 objects were put together, and participants were asked to sort them by placing the correct objects to one side and the incorrect objects to the other side. Controls had no difficulty (95% correct). E. P. and G. P. failed altogether (56% and 50% correct, respectively). E. P. placed nine objects in one group and seven in the other. When he moved to look underneath one of the objects and was stopped by the examiner, he said, “That’s just a habit I think. It’s just, what’s underneath?” So here was a particularly useful example from the domain of habit learning of the distinction between conscious (declarative) and unconscious (nondeclarative) learning systems. For controls, the learning was rapid and resulted in a capacity for flexible use of conscious knowledge. For the patients, the learning was slow and resulted in unconscious, rigidly organized information that was unavailable when testing was conducted in a novel way.

Priming

Priming is a form of nondeclarative memory distinct from skill and habit learning. It is evident as improved access (measured by speed or accuracy) to recently presented items, such as words, objects, or even illegal nonwords (Hamann and Squire, 1997b). Priming was fascinating to me because it occurs entirely outside of awareness. The phenomenon is everywhere, but it is a phenomenon of perception, not an experience of memory. In a splendid review of priming’s early years, Tulving and Schacter remarked, “It is difficult to study phenomena whose existence one does not suspect” (1990, Science, 247, 301–306). An early antecedent used methods that we now know can demonstrate priming (Warrington and Weiskrantz, 1970, Nature, 228, 628–630). Memory-impaired patients exhibited near-normal performance when three-letter word stems (MOT__) were given as cues for recently presented words (MOTEL). Yet, we and others trying to use the same methods often found impaired (not spared) performance (e.g., Squire et al., 1978).

Motor skills, perceptual skills like mirror reading, and habit learning were different, I thought. These develop gradually over many trials, and I was doubtful that patients could perform at an intact level on any test based on single items. I was wrong but eventually made sense of it when we discovered the crucial role of the instructions in determining how individuals approach the task. With standard memory instructions (use this three-letter cue to help you recall a recently presented word), controls showed the expected advantage over patients (Graf et al., 1984). That is, the controls identified more of the study words than did the patients. However, when the instructions were changed so as to discourage a declarative memory strategy (use this three-letter word stem to form the first word that comes to mind), the results were different. Memory-impaired patients now exhibited consistently intact performance, completing word stems to form study words at the same rate as controls.

Priming can last a long time. In one experiment, memory-impaired patients and controls named objects and then two or seven days later named the same objects about 100 msec faster than other objects that had not been presented earlier (Cave and Squire, 1992). This effect occurred despite the fact that the patients were severely impaired at remembering the objects themselves. Another notable feature of priming is that it is diminished by manipulations that scarcely affect declarative memory, such as changing the size or shading of an object that was presented earlier, changing from one object to a different object with the same name (Cave and Squire, 1992), or changing the modality of item presentation (Graf et al., 1985). Thus, priming proved to have the same rigid, inflexible kind of organization that was found in other forms of nondeclarative memory. Priming is presumably advantageous because animals evolved in a world where things that are encountered once are likely to be encountered again.

For many years, a popular idea was that priming provides information that individuals can use to make conscious judgments of familiarity. The idea was that a recently presented item (a word, for example) would “pop out” when encountered later and that this would help with deciding whether the word had been presented earlier. Some proposed that the operation of priming could explain why amnesic patients typically perform a little better than chance (50%) on recognition memory tests for novel and familiar items. Yet it seemed to me that priming usually goes unnoticed. One is not aware that a recently studied object is later named more quickly, and one is often unaware even that the “first word to come to mind” in a word-stem completion task was actually a word from a recent study list.

Initially, we found a way to test whether priming benefitted recognition memory in patients receiving ECT. At an early time after treatment (45 minutes), priming was fully intact, but patients still performed at chance on the memory tests (Squire et al., 1985). Later, we tested the idea in multiple ways with patient E. P. E. P.’s memory impairment was so severe that he consistently performed at chance on recognition memory tests. Yet, he exhibited fully intact perceptual and conceptual priming (Hamann and Squire, 1997a; Levy et al., 2004). In one case, he even performed at chance on the recognition memory test when he was given access to his intact priming response just before the recognition test (Stark and Squire, 2000b). These findings ruled out the idea that recognition judgments of familiarity receive any measurable benefit from the operation of priming, and they emphasized the independence of priming and declarative memory. We subsequently showed directly that priming provides only a weak and unreliable cue about prior occurrence (Conroy et al., 2005).

Some information about the neural substrates of priming came when I had the chance to collaborate with Marc Raichle, Steve Petersen, and others in St. Louis in what turned out to be the first functional neuroimaging study of memory (Squire et al., 1992). The memory condition itself activated the hippocampal region. Priming was associated with a reduction of activity in right posterior visual cortex in the region of the lingual gyrus. It appeared that, following presentation of a stimulus, less neural activity is needed to process the same stimulus again. One possibility is that the second presentation of a stimulus leads to a net reduction in activity together with a sharpened response to the repeated stimulus. In any case, the evidence pointed to independent brain systems supporting priming and declarative memory. Visual priming occurs within perceptual processing systems, where changes occur well before information reaches the medial temporal lobe and visual perception is transformed into visual memory.

Classical Eyeblink Conditioning

In the context of the distinction between conscious (hippocampus-dependent) and unconscious (hippocampus-independent) memory systems, I had always been curious about trace conditioning. Trace conditioning is a variant of classical conditioning. In the case of trace eyeblink conditioning, the conditioned stimulus (CS), such as a tone, is presented and terminated, followed by a short interval of a few hundred milliseconds before presentation of an air puff, the unconditioned stimulus (US). Initially, the US elicits an eyeblink, but with repeated CS-US pairings, the CS elicits a conditioned eyeblink response (CR) in advance of the US. Trace conditioning was known to require the hippocampus. Yet, the trace interval is so short that one would not expect it to cause any difficulty for memory-impaired patients. Even severely impaired patients, such as H. M. and E. P., can easily hold onto information for many seconds. So, why should trace conditioning require the hippocampus?

Bob Clark in the lab had worked with eyeblink conditioning in graduate school (albeit with rabbits) and was interested in the problem. We started with the idea that trace conditioning in humans might require some kind of long-term declarative memory, perhaps knowledge (awareness) about the CS-US relationship across many trials. In our first study, patients with medial temporal lobe damage, including E. P., received differential conditioning with two CSs (a tone and white noise), such that one CS was always paired with the US (CS⁺) and a second CS was always presented alone (CS–) (Clark and Squire, 1998). We compared differential trace eyeblink conditioning with differential delay eyeblink conditioning. For delay conditioning, the CS⁺ was presented a few hundred milliseconds before the US, and the two stimuli coterminated. Delay conditioning was known to be independent of the hippocampus. We also asked a number of questions after conditioning to assess how much knowledge participants had acquired about the temporal relationship between the CS and US (i.e., that the CS predicted the US). The finding was that the patients acquired delay conditioning at a normal rate but failed to acquire trace conditioning. Patients did not learn about the relationship between the CS and US during either kind of conditioning. Controls who did not learn about the CS-US association still acquired delay conditioning but did not acquire trace conditioning. Thus, awareness of the CS-US relationship was irrelevant for delay conditioning but was essential for trace conditioning.

Some suggested that the extra demands of differential trace conditioning (processing two CSs and appreciating their different relationship to the US) might require awareness, whereas the same requirement might not hold for the simpler, single-cue conditioning procedure. Yet, we found the same thing with single-cue conditioning. In a series of experiments, led by Joe Manns in collaboration with Bob Clark, volunteers received 120 trials of CS-US pairings with either single-cue trace conditioning or single-cue delay conditioning. For single-cue trace conditioning, the awareness score achieved after 10 trials correlated significantly (+0.49) with the strength of conditioning (percent CRs) across all 120 trials. In contrast, for single-cue delay conditioning, the correlation was not significant (-0.13) (Manns et al., 2001; see also Manns et al., 2002). Other work emphasized that delay and trace conditioning are fundamentally different phenomena (Clark et al., 2001a). For delay conditioning, CRs were closely related to the strength of the CS-US association. For trace conditioning, CRs were related to expectation of the US, that is, to knowledge that the US would occur.

In an additional study of differential trace conditioning, we tracked the development of knowledge about the CS-US relationship by asking one group to predict on each trial whether the US would occur, and asking a second group of participants whether they would blink (Manns et al., 2000). Asking participants to predict their eyeblinks inhibited the acquisition of awareness about the CS-US relationship as well as the acquisition of trace eyeblink conditioning. In contrast, asking participants to predict the onset of the US promoted both awareness of the CS-US relationship and trace conditioning. Acquisition of knowledge about US onset and acquisition of trace conditioning itself developed concurrently.

This set of studies showed us that the development of awareness (the CS predicts the US) is an essential feature of successful, trace eyeblink conditioning. Awareness did not directly drive the eyeblinks. Indeed, participants typically did not become aware of their eyeblinks or that they were blinking in response to the CS. Yet, awareness of what was being learned (the relationship between CS and US) accompanied trace conditioning, just as in the typical declarative memory task where, if learning is to succeed, participants acquire conscious knowledge of what they are learning (memorizing word pairs, memorizing a route, and so on).

Trace conditioning, like delay conditioning, depends on the cerebellum. Importantly, trace conditioning also depends on the hippocampus and medial prefrontal cortex. We suggested that trace conditioning requires the acquisition of declarative memory because the trace interval (which can be as long as 1000 msec) makes it difficult for the cerebellum to process the CS-US relationship in an automatic, reflexive way (Clark et al., 2002b). Electrophysiological studies have not detected activity in the cerebellum for longer than 100–200 msec following the termination of a single input pulse. However, if the hippocampus and neocortex have represented the stimulus contingencies, then information about the CS and US might be available to the cerebellum in a format it can use (i.e., just before and during the US). Our idea was that awareness during conditioning is a marker, or indicator, that the hippocampus and neocortex are effectively engaged by the task. Awareness is an emergent property of their operation. We also could not resist suggesting that hippocampus-dependent learning in nonhuman animals may be accompanied by some form of awareness.

Recollection and Familiarity

The long-standing distinction between recollection and familiarity refers to two ways in which an item can be recognized as having been presented before. Recollection involves remembering specific contextual details about the episode in which an item was encountered, and familiarity involves simply knowing that an item was presented. I had become interested in this distinction in the course of extended conversations with John Wixted that struck up in the early 2000s. John is professor of psychology at UCSD, accomplished in the cognitive science of memory, and a rigorous scholar. The conversations eventually led to collaboration, and working with John has been one of the pleasures of the more recent part of my career.

At the time, John and I began talking, there was broad interest in how the different structures of the medial temporal lobe contributed to declarative memory, and out of this climate came the proposal that recollection depends on the hippocampus and familiarity on the adjacent perirhinal cortex (Brown and Aggleton, 2001, Nature Reviews Neuroscience, 2, 51–61). John pointed out that studies appearing to support the idea usually involved a comparison between strong, recollection-based memories and weak, familiarity-based memories (Wixted and Squire, 2011). That is, most studies confounded memory strength with recollection and familiarity. I had my own reservations because I was not seeing signs of this distinction in the behavior of our hippocampal patients. They did not express familiarity with test material, while missing only source memory (“where” and “when”) or other details about previous episodes. They simply reported that material was not familiar. In addition, when Jeri Janowsky was in the lab as a postdoctoral fellow and set up a small group of frontal lobe patients, the frontal patients were not amnesic, but they made source memory errors—such as misidentifying where they had acquired information (Janowsky et al., 1989). Source memory errors are errors of recollection. It seemed to me that, whereas the recollection-familiarity distinction might not illuminate hippocampal function, it might be relevant to frontal cortex.

We began discussing how to bring the matter to experiment, drawing on work by Craig Stark in the lab about the construction of fMRI studies and the optimal design of baseline conditions (Stark and Squire, 2000a, 2001). Our approach went in a number of directions, and most of the good ideas were John’s. In one project, led by postdoctoral fellow Brock Kirwan, we designed an fMRI study such that item memory strength and source memory strength could be assessed independently (Kirwan et al., 2008b). Measuring item memory strength independently of source memory (recollection) was intended to measure the strength of familiarity-based memory. Volunteers saw 360 nouns in the scanner, making animate/inanimate judgments when the nouns were presented in green and size judgments (smaller than a shoebox?) when the nouns were presented in red. Subsequently, in a memory test outside the scanner with the 360 old words and 360 new words, participants made recognition decisions (the item-memory question) on a 6-point confidence scale (1, sure new to 6, sure old). Confidence ratings provide a measure of item memory strength. For words judged old, they also made a source memory decision on a 6-point confidence scale about which judgment had been made when the word was studied earlier (1, sure animacy to 6, sure size).

The first analysis was planned to identify brain regions in which the activity at study varied linearly as a function of subsequent item-memory strength, while holding source memory strength constant at chance levels. To do this, we included in the analysis only trials in which items judged old (ratings of 4, 5, or 6) were associated with the lowest possible source confidence (ratings of 3 or 4). Because recollective success (i.e., source memory) was weak and invariant in this analysis, any findings would most likely be related to the success of familiarity-based memory. In this analysis, activity in both the hippocampus and perirhinal cortex predicted subsequent memory strength. Next, we found regions in prefrontal cortex where activity at study varied linearly as a function of subsequent source-memory strength, while item-memory strength was held constant at a high level. In this case, the analysis was limited to correct item judgments with a confidence rating of 6. The absence of a hippocampal finding in this analysis suggested to us that hippocampal activity, when it occurred, was indicative of strong memories rather than recollection per se (Kirwan et al., 2008b). Indeed, other work confirmed that memory strength must be strong before elevated fMRI activity can be observed in the hippocampus (Song et al., 2011c).

Although I found this study particularly compelling, a single study doesn’t always do much to correct a large idea. It is better, I think, to find additional ways to test an idea and to be hit over the head with the data rather than to have to help it along with argument. In the end, we found a number of useful ways to explore the issue, and the topic was with us from my first collaboration with John (Wais et al., 2006) through a novel study developed by graduate student Adam Dede (Dede et al., 2014). Four postdoctoral fellows and three graduate students made significant contributions to 12 research articles, reporting the results of 12 different experimental attacks on the problem (notably, Kirwan et al., 2010; Smith et al., 2011; Song et al., 2011a; Song et al., 2011b; Dede et al., 2013). The memory-strength confound, as we called it, had led many astray. Recognition memory decisions associated with recollection usually reflect stronger memory than recognition decisions associated with familiarity. But recollection can be weak, and familiarity can be strong. When one matches the strength of these two constructs, one finds hippocampal activity in fMRI associated with both recollection and familiarity (Smith et al., 2011).

We ended up with the perspective that hippocampal activity during learning predicts subsequent memory strength, regardless of whether memory is based on familiarity or recollection, whereas activity in prefrontal cortex predicts the success of recollection. Some took this idea to mean that the hippocampus is important only when memory is strong. However, we meant only that memory must be strong to detect hippocampal activity in fMRI, not that the hippocampus plays no role in weak memory.

It was a pretty comprehensive body of work, and our experiments seemed to persuade not a few people. A count of publications in six major neuroscience journals each year that used the terms recollection and familiarity shows a peak of 135 in 2010-2013 but only 24 in 2017-2020. Meanwhile, how medial temporal lobe structures might contribute differently to declarative memory remains a topic of interest. Our view is that the matter will be best informed by findings from neuroanatomy and neurophysiology and that different structures will prove to support different attributes of memory (e.g., visual, auditory, spatial) (Wixted and Squire, 2011).

Memory and Spatial Cognition

For decades now, anyone taking up the study of hippocampal function knows that he or she has taken up a problem guided by two different, and potentially conflicting, traditions of work. One tradition began in 1957 with the description of patient H. M. and emphasizes the role of the hippocampus in memory function. The other tradition began in 1971 with the discovery of place cells in rodents. This tradition does not deny the importance of memory but also identifies a role for the hippocampus in spatial navigation and spatial cognition. There has been much discussion whether and to what extent these two accounts are compatible. One suggestion, which has much to recommend it, is that one account can simply be folded into the other (see “The Role of the Hippocampus in Navigation Is Memory”; Eichenbaum, 2017, Journal of Neurophysiology, 117, 1785–1796).

But not all of the second tradition can be accommodated in this way, and for a long time, I have thought that the two accounts lead to a contradiction. The contradiction arises because a key finding from the memory tradition was that short-term (working) memory is independent of the hippocampus and fully intact in patients such as H. M. Patients (or rats) with hippocampal lesions should therefore be able to perform all manner of tasks, including spatial tasks, so long as a task can be managed within working memory (i.e., by actively maintaining task information in mind). In contrast, some accounts coming from the spatial tradition hold that the hippocampus carries out computations needed for navigating, for locating oneself in space, and for internally constructing spatially coherent scenes. In this view, patients such as H. M. should fail spatial tasks that call on these abilities, even when task performance can be supported by working memory or when a task scarcely requires memory at all.

These ideas don’t directly mandate which tasks are most suitable for deciding between the two perspectives. However, it is possible to present simple tasks that require participants to construct and operate on spatially coherent mental images and that place little burden on memory. For example, we gave hippocampal patients four tasks assessing the capacity for spatial mental imagery (Kim et al., 2013a). One task asked 108 true/false questions, such as: “Between 7 and 9 o’clock, the tip of a clock’s hour hand moves to the left.” Answering this question requires constructing a coherent mental image and making a judgment, but it does not require memory beyond the ability to hold a mental image in mind for a few seconds. The patients performed as well as controls on all four tasks, though as expected, they had difficulty afterward remembering the test materials. In another study, patients did as well as controls at imagining and describing what might lie beyond photographs of scenes that they viewed, and they also used as many spatial referents in their narratives as did controls (Kim et al., 2015). In another task from this same study, patients exhibited the phenomenon of boundary extension, the normal tendency to draw a simple scene immediately after viewing it, such that the scene has a larger background than was actually presented.

In still other spatial tasks, hippocampal patients were fully intact at navigating with hand-held maps (Urgolites et al., 2016), matching spatial layouts to identical layouts presented from a different viewpoint (Urgolites et al., 2017), recognizing scenes after shifts in viewpoint (Rungratsameetaweemana and Squire, 2018), and making possible/impossible judgments about the structural coherence of three-dimensional scenes (Urgolites et al., 2019). In two additional studies, hippocampal patients produced as many details as controls as they tried to imagine plausible future episodes, and they included in their narratives as many spatial details as did controls (Squire et al., 2010; Dede et al., 2016b).

Lastly, valuable information came from a new task developed by Adam Dede. Patients with hippocampal lesions or large medial temporal lobe lesions took a 25-minute guided walk during which 11 planned events occurred. Then, immediately afterward, they narrated what they could remember about the events of the walk (Dede et al., 2016a; Heyworth and Squire, 2019). As expected, the patients remembered many fewer details about the walk than did controls, and they recalled about as much as controls tested 2.6 years after the walk. Nevertheless, patients reported details that had the characteristics of episodic recollection. The pertinent finding was that the patients had no particular difficulty recalling spatial details in comparison to other kinds of details, despite the need to construct spatially coherent images if one is to recollect spatial content. What we found instead of spatial problems were problems with temporal organization. Unlike controls, who tended to recall the events of the walk in chronological order, even after 2.6 years, the patients recalled the events in a haphazard order that had no relationship to the order in which events actually occurred.

Across all these tasks, from mental imagery to episodic recollection, we found no examples of spatial deficits in patients with hippocampal lesions. When we turned to tests of path integration, however, we found something different in rats. Path integration refers to the ability to use self-motion cues as one moves through space to keep track of a reference location. In the study, rats or humans entered a circular arena, searched for a target, and then tried to return to the start location (Kim et al., 2013b). Patients with hippocampal lesions, even patient G. P. with large medial temporal lobe lesions, were fully intact at path integration, presumably as a result of using working memory to hold the start location in mind while searching for the target. The surprise was that rats with hippocampal lesions failed altogether. We were particularly interested in trials that were accomplished quickly, because those trials should afford the best chance for working memory to support performance. Yet, rats could not find their way back to the start location even in the most favorable conditions, when the outward path was less than 1 meter long, when they traveled in a straight line to find the target, and when the target was found within 3 seconds.

Although this result seemed to give weight to the idea that the rat hippocampus supports certain spatial functions, there may be a different way to think about it. Inasmuch as patients appeared to succeed at path integration by relying on an intact working memory, might rats have failed because their capacity for working memory was inadequate for this task? That is, perhaps rats are limited, in comparison to humans, in their ability to construct a coherent working memory of spatial environments. Could the difficulty then lie in limitations of rodent frontal cortex rather than in an impaired spatial function dependent on the hippocampus? More needs to be done on this large topic, but to my mind, evidence from many sources has been moving the discipline toward a broader view that affords the hippocampus and its place cells a role in representing both spatial and nonspatial information that can then be used for the formation of long-term memory (e.g., Buffalo, 2015, Hippocampus, 25, 713–718; Aronov et al., 2017, Nature, 543, 719–722).

A challenge of this kind of work in memory-impaired patients is that only small numbers of patients are typically available to any one laboratory, different methods have been used to determine the locus and extent of neuropathology, and the etiology of the hippocampal damage can vary. In some cases, there has been insufficient attention to neuroanatomy and the likelihood of damage in addition to the hippocampus. I am skeptical that the modest impairments reported by others in a few of the spatial tasks described earlier were due to hippocampal damage itself. For example, can one attribute to hippocampal damage the finding of a modest impairment in three-dimensional scene perception in patients who have less extensive hippocampal damage than our patients and less severe memory impairment as measured by the same memory tests (McCormick et al., 2017, Hippocampus, 27, 303–314; compare with our finding of intact three-dimensional scene perception in Urgolites et al., 2019)? I have been known to claim that, after a year spent with a hippocampal patient, a report of one’s impressions would not include the word “spatial.”

Other Kinds of Memory Impairment

I sometimes get calls from patients, family members, attorneys, or journalists about memory impairment. More often than not, the calls are about what I call “the other kind of amnesia,” functional amnesia, which belongs to the realm of psychiatry rather than neurology. Most published reports are single-case studies. My neurological colleague, Mark Kritchevsky, and I were able to carry out the first neuropsychological study of a series of such patients (n = 10; Kritchevsky et al., 2004). All patients remembered day-to-day events after the onset of amnesia, although some performed poorly on tests of verbal learning. The main finding was substantial loss of past autobiographical memory and a variable pattern of sparing and loss on tests of past public events and famous faces. All patients had a significant premorbid psychiatric history and eight still had retrograde amnesia for personal memories at last contact (median = 14 months after onset). The variability in findings, we suggested, was related to differences between patients in their commonsense concepts about memory and how it works.

Certainly the most unusual call came from the husband of a woman who, since a minor car accident in 2005, had been unable to remember events from one day to the next. Each day, her memories accumulated for the events of that day but then disappeared during each night of sleep. To our knowledge, this presentation was unique to the medical literature, but it had been depicted in the fictional film 50 First Dates (2004). On testing, she demonstrated no memory at all for material she knew had been presented the day before (Smith et al., 2010). However, when testing included some of yesterday’s material, covertly sprinkled in with other material learned earlier on the same day, her memory was good for all of it. Subsequently, she was “cured” after our referral to Paul McHugh at Johns Hopkins, where it was suggested that she interrupt her sleep at 4-hour intervals. The idea was that she could interpret these rests as “naps” and not the full night of sleep that she thought was the cause of her forgetting. Since her case was published, we have received four communications from around the world describing a similar condition. Those who have worked with such patients, including us, have not believed that the patients were consciously simulating their condition. At the same time, it is not well understood when or how or to what degree behavior can be organized and controlled unconsciously.

Final Threads

I am fortunate to have been able to work in the world of science, to have received sustained funding from NIMH (my RO1 is currently in years 42 to 46), to have had funding from the Department of Veterans Affairs for just as long, and to have published in seven calendar decades. I am especially grateful for the support of the late Lewis Judd, long-time chair of the Department of Psychiatry here at UCSD where I have my primary academic appointment. I am also grateful for the support of Gerhard Schulteis, associate chief of staff for research at the VA San Diego Healthcare System where I am appointed as research career scientist.

The work that has been done has depended on the energy of many undergraduate volunteers and research assistants, and on the dedication and talents of 17 graduate students and 24 postdoctoral fellows who are acknowledged by citation in the preceding pages and in the list at the end. But students and postdocs are not enough for work with patients. One can’t send out a stream of trainees to patient homes. The whole operation depends on a senior staff person who can nurture long-term, social worker-like relationships with the patients and their families, do the testing, supervise other research assistants, and work with the students and postdocs. In this role, there was Joyce Zouzounis (20 years) and now Jennifer Frascino (since 1997). Jennifer is research coordinator, tester, supervisor, and collaborator. She is beyond extraordinary, and I am lucky and grateful to have her with us. An administrative assistant was always essential to the lab as well, and I mention two who were long-serving and appreciated by all of us (Lilian Fontana, 12 years, and Sherry Hargrove, 14 years). In 2018, lab members organized a Fest in the form of a symposium and reunion of colleagues, trainees, and staff from around the world.

I am also grateful for the inspiration of three colleagues in the generation ahead of me, also in memory research, whom I have known since graduate school: Mort Mishkin, Jim McGaugh (Volume 4), and Eric Kandel (Volume 9). They were all in my Presidential Symposium at the Society for Neuroscience Annual Meeting in 1994. Mort was unfailingly generous with Stuart and me when we were doing our monkey work. I had the pleasure of introducing him in 2016 when he received the NAS Award in the Neurosciences. Jim is at nearby University of California Irvine. I have visited him for conversation and advice on many occasions and was always the better for it. I wrote a book with Eric (Memory from Mind to Molecules, 2009, 2nd edition), an exhilarating experience, and in 2000, we did a fine piece on the history of neuroscience (Science, 2000, 290, 1113–1120). Eric knows more neuroscience than anyone I know.

I have been driven most of all, I think, by the pursuit of facts and by the job of developing the evidence to make a finding convincing. The presentation should be not just compelling but also beautiful. I am almost more interested in the facts than in their interpretation, though I do know why I did what I did. I like a finding that implies the interpretation, or where the interpretation is obvious, and there is scarcely need for a Discussion section. I think I have sometimes fallen too much into developing experiments to counter work I find misguided, especially when a publication is directed at my own work. Deciding whether to engage in “defensive” experimental work or carry on with one’s own program is a matter worth serious deliberation. My friend, physicist George Feher, once remarked, “You can’t become a saint by showing that someone else is a sinner.”

I have been surprised at the extent to which a scientist sometimes holds onto an idea, despite evidence that, so far as I can tell, completely dislodges it. For some, the idea seems to trump the data, as if the idea is too good to be wrong. I am often reminded of Charles Darwin’s comment about his contemporary, Herbert Spencer, who was inclined toward large ideas. In his gem of autobiography, Darwin wrote: “His deductive manner of treating every subject is wholly opposed to my frame of mind. His conclusions never convince me: and over and over again I have said to myself, after reading one of his discussions, ‘Here would be a fine subject for half-a-dozen years’ work’ ” (The Autobiography of Charles Darwin. Nora Barlow, ed., 1958, p. 109).

In 1993–1994, there were 20,000 members of the Society for Neuroscience when I served a term as president. It was a challenging time, as we were in the midst of deciding if we should bring the Journal of Neuroscience in-house and also find a new editor. I worked closely with my friend Carla Shatz, president-elect, and also initiated this History series (143 chapters through Volume 10), as well as what became 30 edited, broadcast-quality, 1-hour video interviews of leading neuroscientists, collected between 1994 and 2008. All of this is freely available at the Society’s website.

The balance that one is meant to achieve between work and family eluded me, I am afraid, and my absorption in the work was certainly a large factor in the eventual dissolution of two partnerships. But these gifted me with four magnificent children with whom I have remained close: Ryan (1986), Luke (1988), Charlie (2005), and Caroline (2008). One thing that brought us all together was our Vermont house. In 1966, during my time at MIT, and using the poker winnings from Stanford as my share, two friends and I built a house in southeastern Vermont. We were going to build a standard A-Frame, but one of our roommates, a student at the Harvard Graduate School of Design, proposed that he design something for us. The result was a modest, cedar-shingled house overlooking a brook, which I eventually bought out from the others. Over the years, it became a regular vacation place for me and all four children, who love it and have visited every year of their lives.

Outside of science and family, there were two activities that claimed my attention, actually two games: Scrabble and poker. Scrabble is one of the great two-person games. I played tournament Scrabble until it was displaced by the writing of my first book (Memory and Brain, 1987). It fascinated me that this widely popular game, as played in tournaments, is miles apart from the game enjoyed by the average living room player. Even a middling tournament player (like me) would likely outdistance a living room player by 100 points or more per game. Tournaments are played with a chess clock with 25 minutes allocated to each player for the total game. Players know all 105 two-letter words and each of the several hundred three-letter words. It is a contest of letter management and the construction of words that use all seven of one’s tiles. These words (Bingos), garner 50 bonus points, and three or four of them might be played in any one game. Players know how to rotate certain six-letter word strings through the alphabet to find dozens of seven-letter words, most of which no one recognizes as regular words. For example, for the well-known string, SATIRE, one finds ATRESIA, ARISTAE, ASTERIA, BARITES, BAITERS, REBAITS, TERBIAS, ATRESIC, CRISTAE, RACIEST, STEARIC and on it goes. An example of an inside joke is: He had SATIRE plus a blank and couldn’t find a Bingo.

I have continued to play poker ever since Stanford, finding private games in Cambridge, New York, and now in San Diego. Poker is endlessly absorbing. There is knowledge of the game, probabilities, the characteristics of the other players, and tactics. The private game that I currently play in was begun in 1964 by George Feher, who brought it to UCSD from the Bell Labs. The game happens every two weeks and goes for 5.5 hours. Poker in California is legal, so long as the game is not being run for profit. There are more than 20 different forms of poker (e.g., Hold ’Em, Omaha Hi/Lo, Badugi), each requiring seriously specialized knowledge. The very best players sit in mixed games where the game changes every eight hands. Outside our private game, I play two specific games myself (Stud Eight or Better, Big-O) and have occasionally indulged them at the giant casinos of south Los Angeles. I know little about Hold ’Em, currently the most popular kind of poker. I am a good player but am not at the level of the professionals. One finds parallels between poker and science. Each hand is a new experiment, which one should approach without bias. Probabilities bear out, and, as physicist Richard Feynman once wrote, “Nature cannot be fooled.” One sometimes must give up a cherished belief. A promising idea is abandoned, an excellent starting hand is discarded. Considering the time I have invested in this hobby, I am glad to report that I have a lifetime positive outcome.

Coda

As recounted, my early enthusiasm for reading the literature effectively shaped my entire career. A 1971 paper on retrograde amnesia fueled the transition to human memory and human memory impairment. A 1978 paper on the hippocampus led to 21 years of work with nonhuman primates. I think this is all it took to have a satisfying career—the excitement I felt when I read those two papers and the possibilities I could imagine. The rest of it was that I loved it. My reading of the literature in the early days, however, and my enthusiasms, sometimes took me into unfamiliar territory. I remember once trying to describe a finding to Dale Purves.

“Who did it?” he asked.

“I think it was Westrum, something like that. Maybe Wes,” I said.

Dale replied, “Wes Westrum was a catcher for the New York Giants.”

Graduate Students

Postdoctoral Fellows

1970s

Neal Cohen

1970s

Douglas Wetzel

1980s

Ken Paller

Richard McKee

Frank Haist

Wendy Suzuki

1980s

Art Shimamura

Jeri Janowsky

Carolyn Cave

Gail Musen

1990s

Elizabeth Buffalo

Joseph Manns

Nancy Rempel-Clower

Seth Ramus

Edmond Teng

1990s

Barbara Knowlton

Stephan Hamann

Pablo Alvarez-Royo

Paul Reber

Jonathan Reed

Craig Stark

Heike Schmolck

Erin Kitchener

Robert Clark

2000s

Jeffrey Gold

Yael Shrager

Peter Wais

2000s

Nicola Broadbent

Peter Bayley

Daniel Levy

Christine Smith

Brock Kirwan

Kristin Mauldin

2010s

Ashely Knutson

Annette Jeneson

Adam Dede

Amber Ocampo

2010s

Zhuang Song

Soyun Kim

Zhisen Urgolites

Nadine Heyworth

References

Alvarez-Royo P, Clower RP, Zola-Morgan S, Squire LR (1991) Stereotaxic lesions of the hippocampus in monkeys: Determination of surgical coordinates and analysis of lesions using magnetic resonance imaging. J Neurosci Methods. 38: 223–232.

Alvarez P, Squire LR (1994) Memory consolidation and the medial temporal lobe: A simple network model. Proc Natl Acad Sci USA. 91: 7041–7045.

Alvarez P, Zola-Morgan S, Squire LR (1995) Damage limited to the hippocampal region produces long-lasting memory impairment in monkeys. J Neurosci. 15: 3796–3807.

Bayley PJ, Frascino JC, Squire LR (2005a) Robust habit learning in the absence of awareness and independent of the medial temporal lobe. Nature. 436: 550–553.

Bayley PJ, Gold JJ, Hopkins RO, Squire LR (2005b) The neuroanatomy of remote memory. Neuron. 46: 799–810.

Bayley PJ, Hopkins RO, Squire LR (2003) Successful recollection of remote autobiographical memories by amnesic patients with medial temporal lobe lesions. Neuron. 38: 135–144.

Bayley PJ, Hopkins RO, Squire LR (2006) The fate of old memories after medial temporal lobe damage. J Neurosci. 26: 13311–13317.

Bayley PJ, Squire LR (2002) Medial temporal lobe amnesia: Gradual acquisition of factual information by nondeclarative memory. J Neurosci. 22: 5741–5748.

Benzing W, Squire LR (1989) Preserved learning and memory in amnesia: Intact adaptation-level effects and learning of stereoscopic depth. Behav Neurosci. 103: 548–560.

Broadbent NJ, Squire LR, Clark RE (2004) Spatial memory, recognition memory, and the hippocampus. Proc Natl Acad Sci USA. 101: 14515–14520.

Broadbent NJ, Squire LR, Clark RE (2006) Reversible hippocampal lesions disrupt water maze performance during both recent and remote memory tests. Learn Mem. 13: 187–191.

Buffalo EA, Ramus SJ, Clark RE, Teng E, Squire LR, Zola SM (1999) Dissociation between the effects of damage to perirhinal cortex and area TE. Learn Mem. 6: 572–599.

Buffalo EA, Stefanacci L, Squire LR, Zola SM (1998) A reexamination of the concurrent discrimination learning task: The importance of anterior inferotemporal cortex, Area TE. Behav Neurosci. 112: 3–14.

Cave C, Squire LR (1992) Intact and long-lasting repetition priming in amnesia. J Exp Psychol Learn Mem Cogn. 18: 509–520.

Clark RE, Broadbent N, Squire LR (2005a) Hippocampus and remote spatial memory in rats. Hippocampus.15: 260–272.

Clark RE, Broadbent NJ, Squire LR (2005b) Impaired remote spatial memory after hippocampal lesions despite extensive training beginning early in life. Hippocampus. 15: 340–346.

Clark RE, Broadbent NJ, Squire LR (2007) The hippocampus and spatial memory: findings with a novel modification of the water maze. J Neurosci. 27: 6647–6654.

Clark RE, Broadbent N, Zola SM, Squire LR (2002a) Anterograde amnesia and temporally graded retrograde amnesia for a nonspatial memory task after lesions of hippocampus and subiculum. J Neurosci. 22: 4663–4669.

Clark RE, Manns JR, Squire LR (2001a) Trace and delay eyeblink conditioning: Contrasting phenomena of declarative and nondeclarative memory. Psychol Sci. 12: 304–308.

Clark RE, Manns JR, Squire LR (2002b) Classical conditioning, awareness, and brain systems. Trends Cogn Sci. 6: 531.

Clark RE, Reinagel P, Broadbent NJ, Flister ED, Squire LR (2011) Intact performance on feature-ambiguous discriminations in rats with lesions of the perirhinal cortex. Neuron. 70: 132–140.

Clark RE, Squire LR (1998) Classical conditioning and brain systems: A key role for awareness. Science. 280: 77–81.

Clark RE, West AN, Zola SM, Squire LR (2001b) Rats with lesions of the hippocampus are impaired on the delayed nonmatching-to-sample task. Hippocampus. 11: 176–186.

Cohen NJ, Squire LR (1980) Preserved learning and retention of pattern analyzing skill in amnesia: Dissociation of knowing how and knowing that. Science. 210: 207–209.

Conroy MA, Hopkins RO, Squire LR (2005) On the contribution of perceptual fluency and priming to recognition memory. Cogn Affect Behav Neurosci. 5: 14–20.

Davis HP, Squire LR (1984) Protein synthesis and memory: A review. Psychol Bull. 96: 518–559.

Dede AJ, Frascino JC, Wixted JT, Squire LR (2016a) Learning and remembering real-world events after medial temporal lobe damage. Proc Natl Acad Sci USA. 113: 13480–13485.

Dede AJ, Squire LR, Wixted JT (2014) A novel approach to an old problem: analysis of systematic errors in two models of recognition memory. Neuropsychologia. 52: 51–56.

Dede AJ, Wixted JT, Hopkins RO, Squire LR (2013) Hippocampal damage impairs recognition memory broadly, affecting both parameters in two prominent models of memory. Proc Natl Acad Sci USA. 110: 6577–6582.

Dede AJ, Wixted JT, Hopkins RO, Squire LR (2016b) Autobiographical memory, future imagining, and the medial temporal lobe. Proc Natl Acad Sci USA. 113: 13474–13479.

Gold JJ, Squire LR (2006) The anatomy of amnesia: neurohistological analysis of three new cases. Learn Mem. 13: 699–710.

Graf P, Shimamura AP, Squire LR (1985) Priming across modalities and priming across category levels: Extending the domain of preserved function in amnesia. J Exp Psychol Learn Mem Cogn. 11: 386–396.

Graf P, Squire LR, Mandler G (1984) The information that amnesic patients do not forget. J Exp Psychol Learn Mem Cogn. 10: 164–178.

Hamann SB, Squire LR (1997a) Intact perceptual memory in the absence of conscious memory. Behav Neurosci. 111: 850–854.

Hamann SB, Squire LR (1997b) Intact priming for novel perceptual representations in amnesia. J Cogn Neurosci. 9: 699–713.

Heyworth NC, Squire LR (2019) The nature of recollection across months and years and after medial temporal lobe damage. Proc Natl Acad Sci USA. 116: 4619–4624.

Insausti R, Annese J, Amaral DG, Squire LR (2013) Human amnesia and the medial temporal lobe illuminated by neuropsychological and neurohistological findings for patient E. P. Proc Natl Acad Sci USA. 110: E1953–E1962.

Janowsky JS, Shimamura AP, Squire LR (1989) Source memory impairment in patients with frontal lobe lesions. Neuropsychologia. 27: 1043–1056.

Kim S, Borst G, Thompson W, Hopkins RO, Kosslyn SM, Squire LR (2013a) Sparing of spatial mental imagery in patients with hippocampal lesions. Learn Mem. 20: 657–663.

Kim S, Dede AJ, Hopkins RO, Squire LR (2015) Memory, scene construction, and the human hippocampus. Proc Natl Acad Sci USA. 112: 4767–4772.

Kim S, Jeneson A, van der Horst AS, Frascino JC, Hopkins RO, Squire LR (2011) Memory, visual discrimination performance, and the human hippocampus. J Neurosci. 31: 2624–2629.

Kim S, Sapiurka M, Clark RE, Squire LR (2013b) Contrasting effects on path integration after hippocampal damage in humans and rats. Proc Natl Acad Sci USA. 110: 4432–4747.

Kirwan CB, Bayley PJ, Galvan VV, Squire LR (2008a) Detailed recollection of remote autobiographical memory after damage to the medial temporal lobe. Proc Natl Acad Sci USA. 105: 2676–2680.

Kirwan CB, Wixted JT, Squire LR (2008b) Activity in the medial temporal lobe predicts memory strength, whereas activity in the prefrontal cortex predicts recollection. J Neurosci. 28: 10541–10548.

Kirwan CB, Wixted JT, Squire LR (2010) A demonstration that the hippocampus supports both recollection and familiarity. Proc Natl Acad Sci USA. 107: 344–348.

Knowlton BJ, Mangels JA, Squire LR (1996) A neostriatal habit learning system in humans. Science. 273: 1399–1402.

Knowlton BJ, Ramus SJ, Squire LR (1992) Intact artificial grammar learning in amnesia: Dissociation of classification learning and explicit memory for specific instances. Psychol Sci. 3: 172–179.

Knowlton BJ, Squire LR (1993) The learning of categories: Parallel brain systems for item memory and category knowledge. Science. 262: 1747–1749.

Knutson AR, Hopkins RO, Squire LR (2013) A pencil rescues impaired performance on a visual discrimination task in patients with medial temporal lobe lesions. Learn Mem. 20: 607–610.

Kritchevsky M, Chang J, Squire LR (2004) Functional amnesia: clinical description and neuropsychological profile of 10 cases. Learn Mem. 11: 213–226.

Kritchevsky M, Squire LR (1989) Transient global amnesia: Evidence for extensive, temporally-graded retrograde amnesia. Neurology. 39: 213–218.

Levy DA, Stark CE, Squire LR (2004) Intact conceptual priming in the absence of declarative memory. Psychol Sci. 15: 680–686.

Manns JR, Clark RE, Squire LR (2000) Parallel acquisition of awareness and trace eyeblink classical conditioning. Learn Mem. 7: 267–272.

Manns JR, Clark RE, Squire LR (2001) Single-cue delay eyeblink conditioning is unrelated to awareness. Cogn Affect Behav Neurosci. 1: 192–198.

Manns JR, Clark RE, Squire LR (2002) Standard delay eyeblink classical conditioning is indepenent of awareness. J Exp Psychol Anim Behav Process. 28: 32–37.

Manns JR, Hopkins RO, Squire LR (2003) Semantic memory and the human hippocampus. Neuron. 37: 127–133.

Musen G, Shimamura AP, Squire LR (1990) Intact text-specific reading skill in amnesia. J Exp Psychol Learn Mem Cogn. 6: 1068–1076.

Press GA, Amaral DG, Squire LR (1989) Hippocampal abnormalities in amnesic patients revealed by high-resolution magnetic resonance imaging. Nature. 341: 54–57.

Reber PJ, Knowlton BJ, Squire LR (1996) Dissociable properties of memory systems: Differences in the flexibility of declarative and nondeclarative knowledge. Behav Neurosci. 110: 861–871.

Reed JM, Squire LR (1998) Retrograde amnesia for facts and events: Findings from four new cases. J Neurosci. 18: 3943–3954.

Rempel-Clower NL, Zola SM, Squire LR, Amaral DG (1996) Three cases of enduring memory impairment after bilateral damage limited to the hippocampal formation. J Neurosci. 16: 5233–5255.

Rungratsameetaweemana N, Squire LR (2018) Preserved capacity for scene construction and shifts in perspective after hippocampal lesions. Learn Mem. 25: 347–351.

Sapiurka M, Squire LR, Clark RE (2016) Distinct roles of hippocampus and medial prefrontal cortex in spatial and nonspatial memory. Hippocampus. 26: 1515–1524.

Segal DS, Squire LR, Barondes SH (1971) Cycloheximide: its effects on activity are dissociable from its effects on memory. Science. 172: 82–84.

Shrager Y, Gold JJ, Hopkins RO, Squire LR (2006) Intact visual perception in memory-impaired patients with medial temporal lobe lesions. J Neurosci. 26: 2235–2240.

Smith CN, Frascino JC, Kripke DL, McHugh PR, Treisman GJ, Squire LR (2010) Losing memories overnight: a unique form of human amnesia. Neuropsychologia. 48: 2833–2840.

Smith CN, Hopkins RO, Squire LR (2006) Experience-dependent eye movements, awareness, and hippocampus-dependent memory. J Neurosci. 26: 11304–11312.

Smith CN, Squire LR (2005) Declarative memory, awareness, and transitive inference. J Neurosci. 25: 10138–10146.

Smith CN, Squire LR (2008) Experience-dependent eye movements reflect hippocampus-dependent (aware) memory. J Neurosci. 28: 12825–12833.

Smith CN, Squire LR (2009) Medial temporal lobe activity during retrieval of semantic memory is related to the age of the memory. J Neurosci. 29: 930–938.

Smith CN, Squire LR (2017) When eye movements express memory for old and new scenes in the absence of awareness and independent of hippocampus. Learn Mem. 24: 95–103.

Smith CN, Squire LR (2018) Awareness of what is learned as a characteristic of hippocampus-dependent memory. Proc Natl Acad Sci USA. 115: 11947–11952.

Smith CN, Wixted JT, Squire LR (2011) The hippocampus supports both recollection and familiarity when memories are strong. J Neurosci. 31: 15693–15702.

Song Z, Jeneson A, Squire LR (2011a) Medial temporal lobe function and recognition memory: a novel approach to separating the contribution of recollection and familiarity. J Neurosci. 31: 16026–16032.

Song Z, Wixted JT, Hopkins RO, Squire LR (2011b) Impaired capacity for familiarity after hippocampal damage. Proc Natl Acad Sci USA. 108: 9655–9660.

Song Z, Wixted JT, Smith CN, Squire LR (2011c) Different nonlinear functions in hippocampus and perirhinal cortex relating functional MRI activity to memory strength. Proc Natl Acad Sci USA. 108: 5783–5788.

Spanis CW, Squire LR (1987) Stability of long temporal gradients of retrograde amnesia in mice. Behav Neural Biol. 48: 237–245.

Squire LR (1969) Effects of pretrial and posttrial administration of cholinergic and anticholinergic drugs on spontaneous alternation. J Comp Physiol Psychol. 69: 69–75.

Squire LR (1977) ECT and memory loss. Am J Psychiatry. 134: 997–1001.

Squire LR (1986) Mechanisms of memory. Science. 232: 1612–1619.

Squire LR (1989) On the course of forgetting in very long-term memory. J Exp Psychol Learn Mem Cogn. 15: 241–245.

Squire LR (1992) Memory and the hippocampus: A synthesis from findings with rats, monkeys, and humans. Psychol Rev. 99: 195–231.

Squire LR (2009) The legacy of patient H. M. for neuroscience. Neuron. 61: 6–9.

Squire LR, Alvarez P (1995) Retrograde amnesia and memory consolidation: a neurobiological perspective. Curr Opin Neurobiol. 5: 169–177.

Squire LR, Amaral DG, Press GA (1990) Magnetic resonance measurements of hippocampal formation and mammillary nuclei distinguish medial temporal lobe and diencephalic amnesia. J Neurosci. 10: 3106–3117.

Squire LR, Barondes SH (1970) Actinomycin-D: effects on memory at different times after training. Nature. 225: 649–650.

Squire LR, Bayley PJ (2007) The neuroscience of remote memory. Curr Opin Neurobiol. 17: 185–196.

Squire LR, Chace PM (1975) Memory functions six to nine months after electroconvulsive therapy. Arch Gen Psychiatry. 32: 1557–1564.

Squire LR, Chace PM, Slater PC (1976a) Retrograde amnesia following electroconvulsive therapy. Nature. 260: 775–777.

Squire LR, Cohen N (1979) Memory and amnesia: resistance to disruption develops for years after learning. Behav Neural Biol. 25: 115–125.

Squire LR, Frambach M (1990) Cognitive skill learning in amnesia. Psychobiology. 18: 109–117.

Squire LR, Genzel L, Wixted JT, Morris RG (2015) Memory consolidation. In Kandel ER, Dudai Y, Mayford MR, eds. Learning and Memory. New York: Cold Spring Harbor Laboratory Press, 205–225.

Squire LR, Haist F, Shimamura AP (1989) The neurology of memory: Quantitative assessment of retrograde amnesia in two groups of amnesic patients. J Neurosci. 9: 828–839.

Squire LR, John SS, Davis HP (1976b) Inhibitors of protein synthesis and memory: dissociation of amnesic effects and effects on adrenal steroidogenesis. Brain Res. 112: 200–206.

Squire LR, Kuczenski R, Barondes SH (1974) Tyrosine hydroxylase inhibition by cycloheximide and anisomycin is not responsible for their amnesic effect. Brain Res. 82: 241–248.

Squire LR, Liss PH (1968) Control of memory by spreading cortical depression: a critique of stimulus control. Psychol Rev. 75: 347–352.

Squire LR, Ojemann JG, Miezin FM, Petersen SE, Videen TO, Raichle ME (1992) Activation of the hippocampus in normal humans: A functional anatomical study of memory. Proc Natl Acad Sci USA. 89: 1837–1841.

Squire LR, Shimamura A, Graf P (1985) Independence of recognition memory and priming effects: A neuropsychological analysis. J Exp Psychol Learn Mem Cogn. 11: 37–44.

Squire LR, Slater PC (1975) Forgetting in very long-term memory as assessed by an improved questionnaire technique. J Exp Psychol Hum Learn Mem. 104: 50–54.

Squire LR, Slater PC (1983) Electroconvulsive therapy and complaints of memory dysfunction: A prospective three-year follow-up study. Br J Psychiatry. 142: 1–8.

Squire LR, Slater PC, Chace PM (1975) Retrograde amnesia: Temporal gradient in very long-term memory following electroconvulsive therapy. Science. 187: 77–79.

Squire LR, Slater PC, Miller PL (1981) Retrograde amnesia and bilateral electroconvulsive therapy. Long-term follow-up. Arch Gen Psychiatry. 38: 89–95.

Squire LR, Spanis CW (1984) Long gradient of retrograde amnesia in mice: continuity with the findings in humans. Behav Neurosci. 98: 345–348.

Squire LR, van der Horst AS, McDuff SGR, Frascino JC, Hopkins RO, Mauldin KN (2010) Role of the hippocampus in remembering the past and imagining the future. Proc Natl Acad Sci USA.107: 19044–19048.

Squire LR, Wetzel CD, Slater PC (1978) Anterograde amnesia following ECT: An analysis of the beneficial effect of partial information. Neuropsychologia. 16: 339–347.

Squire LR, Wetzel CD, Slater PC (1979) Memory complaint after electroconvulsive therapy: Assessment with a new self-rating instrument. Biol Psychiatry. 14: 791–801.

Squire LR, Zola-Morgan S (1983) The neurology of memory: The case for correspondence between the findings for human and nonhuman primate. In Deutsch JA, ed. The Physiological Basis of Memory. New York: Academic Press, 199–268.

Squire LR, Zola-Morgan S (1988) Memory: Brain systems and behavior. Trends Neurosci. 11: 170–175.

Squire LR, Zola-Morgan S (1991) The medial temporal lobe memory system. Science. 253: 1380–1386.

Squire LR, Zola-Morgan S, Chen K (1988) Human amnesia and animal models of amnesia: Performance of amnesic patients on tests designed for the monkey. Behav Neurosci. 11: 210–221.

Stark CEL, Squire LR (2000a) Functional magnetic resonance imaging (fMRI) activity in the hippocampal region during recognition memory. J Neurosci. 20: 7776–7781.

Stark CEL, Squire LR (2000b) Recognition memory and familiarity judgments in severe amnesia: no evidence for a contribution of repetition priming. Behav Neurosci. 114: 459–467.

Stark CEL, Squire LR (2001) When zero is not zero: The problem of ambiguous baseline conditions in fMRI. Proc Natl Acad Sci USA. 98: 12760–12766.

Stefanacci L, Buffalo EA, Schmolck H, Squire LR (2000) Profound amnesia following damage to the medial temporal lobe: A neuroanatomical and neuropsychological profile of patient E. P. J Neurosci. 20: 7024–7036.

Suzuki WA, Zola-Morgan S, Squire LR, Amaral DG (1993) Lesions of the perirhinal and parahippocampal cortices in the monkey produce long-lasting memory impairment in the visual and tactual modalities. J Neurosci. 13: 2430–2451.

Teng E, Squire LR (1999) Memory for places learned long ago is intact after hippocampal damage. Nature. 400: 675–677.

Teng E, Stefanacci L, Squire LR, Zola SM (2000) Contrasting effects on discrimination learning following hippocampal lesions or conjoint hippocampal-caudate lesions in monkeys. J Neurosci. 20: 3853–3863.

Urgolites ZJ, Hopkins RO, Squire LR (2017) Medial temporal lobe and topographical memory. Proc Natl Acad Sci USA. 114: 8626–8630.

Urgolites ZJ, Hopkins RO, Squire LR (2019) Spared perception of the structure of scenes after hippocampal damage. J Cogn Neurosci. 31: 1260–1269.

Urgolites ZJ, Kim S, Hopkins RO, Squire LR (2016) Map reading, navigating from maps, and the medial temporal lobe. Proc Natl Acad Sci USA. 113: 14289–14293.

Urgolites ZJ, Smith CN, Squire LR (2018) Eye movements support the link between conscious memory and medial temporal lobe function. Proc Natl Acad Sci USA. 115: 7599–7604.

Wais PE, Wixted JT, Hopkins RO, Squire LR (2006) The hippocampus supports both the recollection and the familiarity components of recognition memory. Neuron. 49: 459–466.

Wixted JT, Squire LR (2011) The medial temporal lobe and the attributes of memory. Trends Cogn Sci. 15: 210–217.

Zola-Morgan S, Squire LR (1984) Preserved learning in monkeys with medial temporal lesions: Sparing of motor and cognitive skills. J Neurosci. 4: 1072–1085.

Zola-Morgan S, Squire LR (1985) Medial temporal lesions in monkeys impair memory on a variety of tasks sensitive to human amnesia. Behav Neurosci. 99: 22–34.

Zola-Morgan S, Squire LR (1986) Memory impairment in monkeys following lesions limited to the hippocampus. Behav Neurosci. 100: 155–160.

Zola-Morgan S, Squire LR (1990) The primate hippocampal formation: Evidence for a time-limited role in memory storage. Science. 250: 288–290.

Zola-Morgan S, Squire LR, Alvarez-Royo P, Clower RP (1991) Independence of memory functions and emotional behavior: Separate contributions of the hippocampal formation and the amygdala. Hippocampus. 1: 207–220.

Zola-Morgan S, Squire LR, Amaral DG (1986) Human amnesia and the medial temporal region: Enduring memory impairment following a bilateral lesion limited to field CA1 of the hippocampus. J Neurosci. 6: 2950–2967.

Zola-Morgan S, Squire LR, Amaral DG (1989a) Lesions of the amygdala that spare adjacent cortical regions do not impair memory or excerbate the impairment following lesions of the hippocampal formation. J Neurosci. 9: 1922–1936.

Zola-Morgan S, Squire LR, Amaral DG, Suzuki WA (1989b) Lesions of perirhinal and parahippocampal cortex that spare the amygdala and hippocampal formation produce severe memory impairment. J Neurosci. 9: 4355–4370.

Zola-Morgan S, Squire LR, Clower RP, Rempel NL (1993) Damage to the perirhinal cortex exacerbates memory impairment following lesions to the hippocampal formation. J Neurosci. 13: 251–265.

Zola-Morgan S, Squire LR, Mishkin M (1982) The neuroanatomy of amnesia: Amygdala-hippocampus versus temporal stem. Science. 218: 1337–1339.

Zola SM, Squire LR, Teng E, Stefanacci L, Buffalo EA, Clark RE (2000) Impaired recognition memory in monkeys after damage limited to the hippocampal region. J Neurosci. 20: 451–463.

Michael Paul Stryker

BORN:

Savannah, Georgia

June 16, 1947

EDUCATION:

Deep Springs College, Deep Springs, CA (1964–1966)

University of Michigan, Ann Arbor, MI, BA (1968)

Massachusetts Institute of Technology, Cambridge, MA, PhD (1975)

Harvard Medical School, Boston, MA, Postdoctoral (1975–1978)

APPOINTMENTS:

Assistant Professor of Physiology, University of California, San Francisco (1978–1983)

Associate Professor of Physiology, UCSF (1983–1987)

Professor of Physiology, UCSF (1987–present)

Visiting Professor of Human Anatomy, University of Oxford, England (1987–1988)

Co-Director, Neuroscience Graduate Program, UCSF (1988–1994)

Chairman, Department of Physiology, UCSF (1994–2005)

Director, Markey Program in Biological Sciences, UCSF (1994–1996)

William Francis Ganong Endowed Chair of Physiology, UCSF (1995–present)

HONORS AND AWARDS (SELECTED)

W. Alden Spencer Award, Columbia University (1990)

Cattedra Galileiana (Galileo Galilei Chair) Scuola Normale Superiore, Italy (1993)

Fellow of the American Association for the Advancement of Science (1999)

Fellow of the American Academy of Arts and Sciences (2002)

Member of the U.S. National Academy of Sciences (2009)

Pepose Vision Sciences Award, Brandeis University (2012)

RPB Stein Innovator Award, Research to Prevent Blindness (2016)

Krieg Cortical Kudos Discoverer Award from the Cajal Club (2018)

Disney Award for Amblyopia Research, Research to Prevent Blindness (2020)

Michael Stryker’s laboratory demonstrated the role of spontaneous neural activity as distinguished from visual experience in the prenatal and postnatal development of the central visual system. He and his students created influential and biologically realistic theoretical mathematical models of cortical development. He pioneered the use of the ferret for studies of the central visual system and used this species to delineate the role of neural activity in the development of orientation selectivity and cortical columns. His laboratory pioneered the modern use of the mouse visual system, demonstrating rapid activity-dependent plasticity during a defined critical period and delineating distinct molecular mechanisms responsible for temporally distinct phases of plasticity. In collaboration with the Feldheim group at UCSC, he revealed the interaction between neural activity and molecular signaling mechanisms responsible for the formation of azimuth maps in V1 and superior colliculus and the connections between them. His and the Alvarez-Buylla laboratory discovered that transplantation of embryonic inhibitory neurons into postnatal visual cortex induces a second critical period of juvenile plasticity. His laboratory made the fundamental discovery of the regulation of V1 cortical state by locomotion and delineated much of the neural circuitry responsible.

Michael Paul Stryker

Chance and Choice: Recollections of a Life in Science

Origin and Early Life

My parents could not have been more different from one another, and only in the circumstances of World War II would they ever have met and married. My father was a southern Catholic raised in Memphis, Tennessee, descended from early residents of New Amsterdam via Penn Yan, New York. His grandfather, George Bailey Stryker, had been an inventor and entrepreneur who built a factory that made a particleboard from cotton husks and stalks. The family lost all its money in the Depression to the point where my father and his cousins were sent to work on the farms of distant relatives during the summers so that they would eat well there. My father did manage to go to the University of Mississippi for an accelerated bachelor’s degree of science in engineering before enlisting in the Army after Pearl Harbor. The Army sent him to a civil engineering graduate course at Yale and ultimately to a landing ship tank that left Puget Sound with an engine room, but with its superstructure to be constructed en route to islands in the Pacific. The ship carried an all African-American engineering battalion commanded by all southern white officers. They invaded and built air fields on a succession of islands and ended up on Okinawa in preparation for the invasion of Japan.

My mother was the second child of Jewish atheist immigrants from Galicia who had fled the pogroms for New York, ending up in Newark, New Jersey. Her mother was one of nine siblings, eight of whom immigrated to the United States over a 15-year period; the last sibling had to go to Brazil instead after U.S. immigration was closed to east European Jews. My mother’s much-older brother was an intellectual, dirt poor but educated at City College and friends with many struggling New York artists, writers, and actors of the 1920s like the Provincetown Players on MacDougal Street in Greenwich Village. He took his young sister there to premiers of Eugene O’Neill plays and hung out afterward with the creators. My mother worked her way through nurse’s training and was at New York Hospital at the time of Pearl Harbor. She enlisted in the Army Nurse Corps and was sent to the Pacific, where she took care of injured Merrill’s Marauders and the air crews that flew “the hump” from Burma to Chunking. She, too, was sent to Okinawa for the invasion.

With a few hundred nurses on an island with more than 50,000 U.S. soldiers, it seems unlikely that my mother and father should have met, fallen in love, and become engaged. I can only imagine that each was searching for something different from what was expected of them—a nice Jewish doctor for my mother and a southern belle for my father. As it turned out, they were the only members of that generation of their two large extended families to marry outside their cultures.

My mother returned to her family in Newark a few months after VJ Day. My father’s unit took much longer to get home. He had encouraged my mother to visit his family in Memphis, where she felt she was shunned by everyone except the ailing matriarch, my father’s great grandmother, who appreciated the nursing care that my mother provided for a couple of weeks. My parents were married in New Jersey about a week after my father returned from the Pacific, and I was born 10 months later. It seemed that the New Jersey family was less hostile to my father than the Memphis family had been to my mother, or perhaps he just had thicker skin. In any case, we never lived near either side of the family all the time I was growing up. It is only in my generation that the cousins have become friends.

My father worked as an engineer and later superintendent for construction companies that built public infrastructure, things like airfields and water and sewage plants. From the time I was born in Savannah, Georgia, until I was six, we moved to eight different cities, mostly in the southeast. My three brothers were born at about three-year intervals after me. From the beginning of my first grade, we moved less frequently, at two-year intervals. The result was a close family, with the ability to make new friends fairly quickly, but with a high degree of self-sufficiency. I was usually happy to read books by myself when there was no one I knew to play with.

We were tremendously lucky to move to a very small town on the side of a wooded mountain across the river from Williamsport, Pennsylvania, when I was six. First- and second grade were in a tiny school with fewer rooms than grades and a beautiful outdoor environment. School was easy for me, and I didn’t like to sit still or keep my mouth shut. As a result, I was the only student repeatedly paddled by the first-grade teacher. The mild paddling was humiliating, but the only injury was to my ego, and it helped me become less disruptive between blessed recess periods. My parents learned about the paddling only at the year-end parent-teacher conference when the teacher, who looked like Mrs. Santa Claus, confessed that her ancient ruler, with which she had paddled the chair of the school board 35 years earlier when he was in first grade, had broken on me. My father made a lovely hickory paddle for her the following week. I will always admire the respect that this wonderful teacher showed for me by not complaining about my behavior to my parents and by treating me as a young person able to improve and become more civilized. Her instruction using a phonetic approach to reading was so good that by the end of first grade I could read adult magazines and books, although I preferred The Hardy Boys and Tom Swift Jr., along with Popular Mechanics.

In that small town, I and two friends my age worshiped a neighborhood boy four years older who let us help him make soapbox derby racers, take apart and repair gasoline lawnmowers, and make a go-kart. He allowed us to come on all-day hikes and helped us climb cliffs that would have terrified our parents had they known. This small rural town gave us a sense of freedom and self-sufficiency that few children today can experience. It is sad that all of the children we knew who went on to college had to leave that town for jobs elsewhere.

Life for the next few years was quite ordinary, with new schools every other year. The most unusual feature of my upbringing in those years was that my father gave me word problems that taught me mathematics—algebra in third grade, logarithms in fifth, and calculus in sixth grade. He did not pose them as math problems, but as physical ones. One I recall clearly because I struggled with it for some time was calculating how long it would take for an inverted pyramidal sink to drain. I knew that it would drain at a definite time, and my father confirmed that the amount of water flowing down the drain would be proportional to the depth of water in the sink. I calculated the time to drain inch by inch, then quarter inch by quarter inch, but I did not know how to calculate it exactly, or even approximately other than by brute force. Only then did he show me the tricks that everyone learns in first year calculus—equations with derivatives and integrals.

For my seventh-grade year, we moved to a house in Winthrop Harbor, a small town in Lake County, Illinois, that was 200 m from Wisconsin and 300 m from Lake Michigan. After some standardized tests early in the year, the principal of the small junior high school called my parents in and told them that his school could not give me an appropriate education and that he wanted to put me in eighth grade immediately so that I could go to high school more quickly. Combined with my being the only new boy in the school, this change engendered some resentment. I was also the smallest boy in seventh grade, and by far the smallest after I was moved to eighth, so I was beaten up by the other boys quite a few times until I learned to fight well.

Apparently, Lake County had never voted Democratic in a national election since the Republican Party was founded, and our town was ultraconservative and dominated by the American Legion veterans’ organization. Even though both of them were war veterans, my parents were excluded and regarded as Communists because they believed in civil rights for Negroes (as African Americans were then called) and were registered Democrats. It was galling to the community when I received the two academic scholarships awarded at eighth-grade graduation—one of which was from the American Legion. The openly expressed racial and religious prejudice that led to my parents’ exclusion from the community had the good effect that they were forced to find adult company in the Unitarian fellowship in Racine, Wisconsin. The Unitarians were then and for many years thereafter one of the few majority white organizations to join in the civil rights struggle led by the black churches in the south.

There were so few people like my parents in Lake County that they became de facto party leaders despite having lived there for only one year, and we were invited to the Democratic Party picnics at Adlai Stevenson’s farm. My first year in high school (ninth grade) in Zion, the larger town to whose school Winthrop Harbor students were sent, was also the year of the first televised presidential debates, between Kennedy and Nixon. To foster civics education, the principal of the high school scheduled debates between two students in front of the whole school for the day after each of the four television debates. Many seniors vied to be the surrogate Nixon, but there were no volunteers to take Kennedy’s part from the 10th, 11th, or 12th grades, and only one, me, in the 9th grade. So I debated as the liberal candidate against different seniors. This practice of standing up for unpopular views served me well years later in my scientific career.

For me that year was bearable because of two outsider ninth-grade friends, one an Armenian who came to the United States with his family via Persia, Lebanon, and Brazil, and was fluent in all of the languages of his earlier life, and the other a local Robert Redford look-alike farm boy who read too widely to be content with the prejudiced attitudes of the community. Our greatest joy was making rockets that we launched from the Lake Michigan beach. Looking back, it seems only good luck that we did not blow ourselves up. After getting some rockets with single-shot cameras 2,000 ft into the air, our rocket career ended with launch of our 4-ft stainless-steel magnum opus, with a ceramic nozzle. It blew up on the launch pad and started a fire in the woody area above the beach. Hearing the sirens, we ran from our slit trench and fortunately were never caught.

For 10th grade, we moved to Oxon Hill, Maryland, a then mostly rural suburb of Washington, D.C., south of Anacostia near the Naval Research laboratory on the Potomac River, with many military and State Department families who moved as often as we had. As I recall, the 4-H Club was the largest student organization in the high school. However, nearly all the fathers of the students in the science club except mine had doctorates. The school had a few inspiring teachers—an English teacher for me; and, while sometimes oppressive, the school generally did all it could to make life easy for its best students, never penalizing me for missing school to do civil rights activities or regional theater, and sending me to the University of Maryland in the evenings for a graduate-level history seminar.

Civil rights activities, mostly through the Unitarian youth groups, were also important to me during high school. Virginia was a southern state, and its schools were then still mostly segregated, despite the seven years that had passed after the Brown v. Board of Education decision. Many of its restaurants refused to serve African Americans, and we high school students went in nice dresses, sport coats, and ties in mixed-race foursomes, after which we circulated to area churches a boycott list of restaurants that would not seat us. Participating in marches and protests, like the 1963 one on the mall at which Martin Luther King gave his “I Have a Dream” speech and Peter, Paul and Mary sang, made us feel as if we were doing something worthwhile. Later, I regretted that, apparently lacking the courage of my convictions, I had not gone down to Alabama and Georgia with some of my friends to work on voter registration during the summers of 1962 and 1963. I was consumed by guilt for not being in Selma when our Unitarian youth group leader, the Reverend Jim Reeb, was murdered during my first year of college.

Never a sports star, I enjoyed my only experience as the object of cheerleading when our school’s team won the championship for two years in a row on what became the longest-running television quiz show in history, It’s Academic, competing against the Montgomery County and other east-coast schools that were more highly regarded. We won again after my two teammates from the grade above mine left for college at Harvard and Caltech.

A highlight from my high school years was a National Science Foundation (NSF) summer program in mathematics and computers at Virginia Tech in Blacksburg. There I was, for some weeks, given sole charge of the school’s IBM 1620 from sometime after midnight to 5 a.m. to write a Simplex Method code that checkpointed itself frequently so that it could restart from where it left off after the computer broke down and was repaired. This was necessary for the program to run to completion because the computer broke down frequently; the IBM repair people seemed always to come within an hour or two after being summoned. This early experience with computers was crucial four years later to my becoming a neuroscientist.

A second high-school highlight was the production of an unauthorized satirical antiwar newspaper that got me and my co-conspirators expelled near the end of the year. The school administration realized they had made a mistake in expelling all of the school’s few students who had been admitted to selective colleges, and they let us return to school and graduate.

College Years

In my junior year of high school, after doing well on the PSAT, I received an intriguing brochure from the Telluride Association, one of the two surviving educational projects of L. L. Nunn (Newell, 2015), who built the world’s first long-distance AC transmission line and founded the electric power industry in the western United States. The Telluride Association ran summer programs in philosophy, the arts, and politics at Cornell for bright high school students. I was already planning to go to the NSF summer program in mathematics and computers at Virginia Tech, so it was the back page of the brochure that intrigued me—a description of Deep Springs College, L.L. Nunn’s other surviving project, a long-running educational experiment founded in 1917. Deep Springs, located in a high-desert valley on the California–Nevada border, had only 5 professors and 25 students pursuing an educational program in an intentionally isolated community that combined rigorous academics with genuine student self-government and labor to run a cattle ranch. After two or sometimes three years at Deep Springs, students transferred elsewhere for the final two years of their bachelor’s degree. After learning about Deep Springs, my plan to go to Yale, where I was offered enough scholarship support to make it possible, seemed too conventional.

Never having been west of the Mississippi, I flew at age 16 to Los Angeles to catch a bus up the Owens Valley to Deep Springs. My father’s parting words, as I boarded the airplane, were “Son, if you are going to do something that will worry your mother, don’t write home about it.” Deep Springs was a fantastic adventure as well as a spectacular education in academics, responsibility, and self-reliance. I arrived thinking that I wanted to be a poet like the one I most admired, Gerard Manley Hopkins. An intensive writing and literature class for the 11 new students with our Rhodes Scholar professor cured me of that ambition but gave me an appreciation for rhetoric and “the grand style” of 18th-century writing. The calculus courses over the two years used the same curriculum as at Caltech and inspired in me the hope that I could be a mathematician as our class size dwindled from 10 to 2 or 3. Economics, philosophy, and music theory courses all had one or two students and did a regular college year’s work in one semester. The German course was taught by a former Polish cavalry officer who told us that he was prompted to escape from a prisoner-of-war camp by the German commandant shortly before the other captives were executed only because he could discuss literature and high culture using the subjunctive properly. The professor required us to memorize tens of lines of poetry for each class meeting. I still love reciting German romantic poetry; indeed, doing so mentally was the only way I avoided screaming from claustrophobia during my one cranial MRI 50 years later.

The unique self-government of Deep Springs gave me experience in working effectively with very different people. It also gave me an opportunity in taking responsibility, first for the community water supply by repairing its 50-year-old redwood pipeline, and later for the herd of 250 cattle through five months of a winter and spring. Finally, it also gave me practice in leadership, as the labor commissioner responsible for the work assignments of all the other students to meet the needs of the college and ranch.

The only element of my ideal liberal arts education that Deep Springs lacked was women. I managed to see my high-school girlfriend, who studied fruit fly biology at the University of Michigan, by hitchhiking to Ann Arbor, and I looked forward to transferring with her to Yale for our junior years, which we understood had proposed to become coeducational in the fall of 1966. Yale deferred coeducation, and I certainly did not want to continue at a single-sex institution. My Deep Springs math teacher told me that the mathematician he most admired, the Hungarian Paul Halmos, was on the faculty at Ann Arbor and that I should go there to study with him. Ann Arbor had the additional advantage of having a leading philosophy department, the other subject I was most interested in. So off to Ann Arbor I went, landing in the campus that was a center of anti–Vietnam War activities.

Ann Arbor was huge, the opposite of Deep Springs, and I found myself with five other students in the junior year of the honors math program. I struggled during the first semester, never finishing more than 30% of a test, and I was certain that they were going to kick me out. They didn’t, and only midway through the year did I find out that all but one of us were in the same boat and were thought to be doing fairly well. The one student, however, was qualitatively different—he not only finished the exams but also proved additional related theorems. It became clear to me that I could never become a creative mathematician—they seemed to have a different kind of mind, like musical prodigies. I needed to find something else to do, something at which I could hope to excel.

At this point, working on antiwar activities became important for my sanity—helping to organize teach-ins, giving speeches, and doing what I thought was important work for society. By the next year, I was disgusted to see that most of the students were not so much antiwar as they were antidraft, wanting to preserve their deferments that kept them from joining the mostly poor people sent off to fight and die in that immoral colonial war. The next year, I gave up with the students and worked on Gene McCarthy’s antiwar presidential campaign in my spare time. It is hard to convey the joy in our car coming back to Ann Arbor from campaigning in Milwaukee for the Wisconsin primary when we heard on the radio LBJ’s speech stating that he would not run for reelection. We never dreamed, of course, that LBJ’s decision to bow out would lead to Nixon’s election.

Not smart enough to excel at mathematics, I switched my major to philosophy because I thought it was interesting and important. I continued to take what I then thought of as real science courses, physics and chemistry, but not biology, catching up on what was not offered at Deep Springs. Staying awake through philosophy lectures, even by philosophers whose written work I admired, proved a challenge, but the questions of meaning, ethics, epistemology, aesthetics, and mind were exciting. I thought that the argument of my philosophy honors thesis was an important one, and I could not see how its conclusion had escaped the leaders of the field: that many philosophical arguments about the distinction between necessary and contingent truth were empty because they depended on contingent facts about the meaning of words. Not surprisingly, the philosophers hated what I wrote, and I came to believe that real philosophers just wanted to keep arguing, even when a conclusion had become clear.

With three younger brothers for my parents to educate, I wanted to cost them as little as possible, so beginning after Christmas of my junior year I looked for the highest paying job available to undergraduates who could work 20 hours per week. Cleaning rat cages was the winner—it was considerably more lucrative than any other, even counting the necessity for an unpaid shower and a change of clothes afterward. The Brain Research lab, in a falling-down Civil War–era hospital at the edge of campus, was the domain of James Olds, co-discoverer of self-stimulation, the so-called pleasure centers of the brain. His wife, Marianne E. (Nicky) Olds, who had done her doctoral work with the famous Harvard philosopher Willard Van Orman Quine, functioned as the lab manager and was my boss. I enjoyed chatting with her about philosophy and was invited to see what was going on in the lab and to come to the Saturday morning meetings of all personnel, where the criticisms of research presentations could be blistering. In those days, the goal of the lab was to map out the brain regions mediating self-stimulation to locate the neural circuit responsible for reward. Large numbers of rats with stimulating electrodes in different brain sites worked in cages with the stimuli controlled by transistor logic boards wired together with relays; any change in the experiments required rewiring. A Digital Equipment PDP8 computer had just arrived, said to be the first one to have left Massachusetts. I told Nicky that I knew how to program computers and could work with Phil Best, an assistant professor in the group, to make it replace all the hard-wired logic boards used to control and monitor experiments. Thereafter, I no longer had to clean rat cages.

The PDP8 would barely be recognized as a computer now: it had 12-bit words, 4096 memory locations, no operating system, and was programmed in machine language. When you turned it on, you had to set switches on its console to put a program in memory that would read a paper tape with holes punched into it that allowed it to drive a teletype. But it could in principle be made to control and monitor the rat experiments using analog-to-digital and digital-to-analog converters and draw graphs on a pen plotter. I programmed it to, among other things, write letters and numbers on the plotter so that we could annotate experiments, and my first publication (after the newspaper that got me expelled from high school) was this program (in the Proceedings of the Digital Equipment Users Society). More important, I became actively involved in the lab and got to know Jim Olds, whom I have regarded ever since as a genius who surely would have won the Nobel Prize had he not died young. I read extensively about brain research, and despite my never having taken a biology course since high school, he and Dr. Best let me carry out an experiment of my own design using cortical spreading depression to probe the laterality of learning a visual task. The endless arguments of philosophers, based on shaky evidence, came to seem tedious to me, and I thought that we in the Brain Research lab might make real progress toward figuring out how the mind actually worked.

Peace Corps in East Africa

Midway through my senior year, I had to decide what to do next. I felt that I had been in school all my life up to that point and that the easy path was to go to graduate or medical school just because I had been good at that sort of thing. I also felt an obligation to serve the country some way other than by going to war, and I had long been interested in East Africa and Kenya’s struggle for independence, having followed the careers of inspiring figures like Jomo Kenyatta and Tom Mboya, a Jack Kennedy–like figure in Kenyan politics. British Prime Minister McMillan had given his “Wind of Change” speech committing Britain to freeing its African colonies, and the former colonies were trying to succeed in the first few years after independence. President Kennedy had created the Peace Corps to help these new countries. I decided that I wanted to go to East Africa as a Peace Corps volunteer.

Like Deep Springs, the Peace Corps was a great adventure. My experience as a land surveyor (taught by my father) and in designing and constructing an extension of the irrigation system at Deep Springs qualified me for a job as an “assistant hydraulics engineer” for the government of Kenya. The others in this job were actual engineering graduates. At that time, there were only four East African graduate engineers in all of Tanzania, Uganda, and Kenya, so that except for a big hydroelectric project done by USAID contractors, most of the water engineering in Kenya was done by about 15 Peace Corps volunteers, a similar number in total of Swedish and Dutch volunteers, and about 20 British contract engineers. In Peace Corps training at a former prisoner-of-war camp in Bismarck, North Dakota, we learned Swahili and the cookbook engineering needed to design water distribution systems before going to Africa. At independence, the government of Kenya had purchased the huge (20,000 acre+) European farms that their owners wanted to sell and divided them up into hundreds of 10–40 acre plots to sell to the former employees of each farm. Once in Kenya, we volunteers met with the new farmers and arranged with them to get loans to distribute water for domestic and dairy use to each plot. With a slide rule and aerial photographs and stereo glasses, along with some finished contour maps, I designed the water systems under kerosene lanterns at night and constructed them during the day with labor contributed by each farm that was to be served. I spoke only Swahili for weeks at a time and became part of the community—we volunteers were very popular because the communities wanted and needed the water systems. Zebras, all kinds of antelope, warthogs, and water buffalo were a continual presence in my yard, along with occasional scarier things, and during several breaks I took trips with other volunteers to many of the famous sights of that part of the world. Life was genuinely thrilling.

Nevertheless, after a year and some months, I wrote to my brother and asked him to send me the giant book I had seen just before my departure from Ann Arbor: Neuroscience: A Study Program (Quarton et al., 1967). I found myself wanting to think about the mind and how it could be studied scientifically rather than continuing to work in development or in the foreign service as some of my fellow volunteers did, some of whom later became U.S. ambassadors. I decided to apply to graduate school. By this time, the Olds lab had moved to Caltech. I was sure that Jim Olds would have me as a student, but I felt that I had learned much of what he would have to teach me, and if I were to go to Caltech I wanted to work with Roger Sperry. I wrote to a friend there to ask if Sperry liked graduate students and heard that he did not. My first choice was then the Institute for Neurological Science at Penn, where the work of Jim Sprague and C. R. Gallistel intrigued me, but I was not accepted there—perhaps not surprising for a philosophy and mathematics major who had never studied any biology. In the giant book, the only neuroscience book that I had, were several fascinating articles from members of the new department at MIT called Psychology and Brain Science. By some miracle, MIT accepted me, probably because they knew that Caltech had done so, and I decided to go there. After this decision, I wrote a long letter to Professor Gallistel outlining the neurophysiological experiment that I thought would answer a question he was pursuing by other means, and two weeks later got a thoughtful reply together with an acceptance at Penn and the offer of a fellowship. But it was too late—I was looking forward to MIT.

Graduate School at MIT

Five days after returning from East Africa, in 1970, I drove my motorcycle from my parents’ house near Washington, D.C., up to Cambridge and found the remnants of a commune, “The Old Mole,” to live in together with three Quakers who had been active in the antiwar movement. From what I had read in East Africa, Professor Peter Schiller’s work on vision in human subjects and alert monkeys seemed most exciting, so I was slated to join his laboratory. He, however, was on vacation with his family on an island in Maine for another couple of weeks. During those weeks, four different senior graduate students came to me one by one to say that I would hear horrible things about Professor Schiller and that, while they were true, I should not change my mind about working with him because it would be worth it. They were correct. Peter taught me how to be the scientist that I am.

It is hard to convey the excitement and the exhaustion of the first year and one half of graduate school. While the five of us in my entering class had a half-day seminar three times a week that involved massive night time reading, the rest of my time was spent in Peter Schiller’s laboratory. Other alert-monkey laboratories spent months training monkeys to fixate a spot of light on a screen before making recordings. During these periods of fixation, the eyes remained in known position, and one could plot visual receptive fields, which are fixed on the retina. Peter had devised a creative strategy that allowed him to study the relationship between eye movements and vision in untrained monkeys—immobilizing one eye by sectioning the nerves that innervate the eye muscles (the fourth and sixth cranial nerves and the ophthalmic portion of the third cranial nerve). The surgery was almost impossibly difficult, and the immobilized eye was then patched so that the animal did not have double vision. Because most eye movements are conjugate, where the two eyes move at the same time and by the same amount, he could study eye movements of the intact eye and then occlude it and remove the patch over the immobilized eye to study visual responses. I got a notion of what the senior graduate students had warned me about when one day Peter did not show up for the difficult monkey surgery, in which I had always assisted, leaving a telephone message that I should do it. I did it, a real challenge. I probably would not have agreed to do so if he had asked me the day before.

For the first few months, Peter would set up a monkey with an electrode in the frontal eye fields, and I would record from neuron after neuron, studying it in relation to eye movements and never finding a visual receptive field. We then went on to study the superior colliculus, where we found visual and eye-movement cells in different layers, and some cells that were active with both visual and motor activity. When we stimulated through the recording electrode, we made the discovery that activating those cells caused an eye movement that brought the eyes to fixate on the location of the visual receptive field. This was a major discovery, and it gave me the enormous satisfaction of seeing two figures I had drawn for our paper (Schiller and Stryker, 1972) appear in the next edition of Mountcastle’s Physiology, the definitive textbook used in most medical schools.

Our major competitors in this area were Bob Wurtz and Mickey Goldberg at the National Institutes of Health (NIH), who used trained monkeys and studied both the frontal eye fields and superior colliculus. They had found that many of the frontal eye field neurons had visual receptive fields, and I was therefore convinced that we and they must have been recording from different areas. I went down to the NIH, and Bob generously showed me the histology with their electrode tracks, confirming that the brain areas were exactly the same. From this I concluded that the frontal cortex was amazingly plastic, and that the visual receptive fields had been created by the fixation training, a hypothesis that has by now received lots of support from other studies, but one which has never been rigorously confirmed by studying the same neurons before and after training.

Wurtz and Goldberg scooped us on some of our colliculus work, but our rivalry was also one of friendship and mutual respect. When their paper (Wurtz and Goldberg, 1971) was accepted in Science before ours was out, they sent us copies of the galley proofs, which we read in the dim light next to our monkey rig. They concluded that these superior colliculus neurons were modulated by attention, as indicated by the monkey’s looking at the place where the visual receptive field had been, whereas we thought of them as being command motor neurons for moving the eyes, as well as having visual responses. Peter Schiller’s joyful comment was “They missed the boat—no, they missed the ocean!” It is interesting that the idea of attention, something we thought at the time to be soft and unscientific, has persisted as its neural substrates have gradually been uncovered, as has the notion of the superior colliculus’s containing command motor neurons.

Rivalries like ours with Wurtz and Goldberg are tremendously positive for neuroscience, particularly when the groups are pursing different approaches to the same end. We certainly worked harder knowing that they were onto the same problem, and we clarified our thinking and experiments as ammunition for our conclusion against theirs, yet both groups shared everything they knew when we met. It really was us all working together against the unknown. Peter’s and my later experiments on the superior colliculus, including turning on and off its cortical input by cooling, were more fun and satisfying than almost any I have done since (Schiller et al., 1974).

Thesis Project

After my apprenticeship working directly with Peter, he set me free to pursue my own choice of thesis project. I was fascinated by the question of how the brain organizes its precise connections during development, and I had made my own mathematical models of self-organizing systems. While Hubel and Wiesel (1963) had concluded that the organization of the visual cortex was innate, with receptive fields in very young, visually inexperienced cats having basic properties similar to those in mature animals, young colleagues of Horace Barlow at Berkeley, including Jack Pettigrew and Colin Blakemore, presented exciting evidence that visual experience organizes responses (and presumably synaptic connections) in the cortex during early life. The most dramatic reports were Pettigrew’s (1974) that neurons required visual experience to become selective for stimulus orientation and Blakemore and Mitchell’s (1973) report that all of the neurons in the visual cortex of cats deprived of vision except for parallel stripes inside a cylinder became selective for the orientation of the stripes. I remember the sentiment among most participants at the Rochester vision meeting in 1972—that it was a shame that Hubel and Wiesel had not yet been awarded their Nobel Prize because their error concerning the innate organization of the visual cortex would detract from their otherwise-monumental discoveries and disqualify them as candidates. This sentiment appears crazy in retrospect, but I shared it. My thesis proposal was to figure out the mechanism of this self-organization by first making it happen on the table in an anesthetized cat.

This work required that I raise cats so that they had absolutely no visual experience and ensure that the neurons studied were a representative sample from the visual cortex that could not have come from a single orientation column. Fortunately, Alan Hein’s laboratory at MIT had a room for total dark-rearing of cats, and I optimized electrode penetrations to travel parallel to the layers of the visual cortex, nearly perpendicular to the columns. The greatest challenge for my experiments, however, was to come up with a way to measure the selectivity of cortical responses quantitatively and objectively. Peter also needed to do this for experiments that he planned. At just that time, our department had installed its first PDP11 computer, and it was in a room next to our physiology lab. This was a time long before bit-mapped video monitors were available, and the only way to produce sharp, orientated contours for visual stimulation was with a slide projector. Peter designed a rectangular mechanical aperture that could be rotated 360 degrees and whose four sides could be positioned independently, all using stepper motors. We mounted this in an optic bench, essentially a fancy slide projector, and moved the image of the aperture using galvanometers with mirrors. I wrote the code and wired the electrical interface that allowed the computer to control the optic bench and to record the trigger pulses set off by an action potential in the neuron we were recording. Together, we had created the world’s first computer-driven optical display capable of producing randomly interleaved light bars of arbitrary size and orientation. This was precisely what we needed for quantitative results.

While the quantitative system was under construction, I went ahead with my proposed experiment on my own, recording from a few single neurons that had to be in different orientation columns for many hours and repeatedly mapping their orientation selectivity by hand, as everyone else had always done, between hours-long sessions of exposure to parallel stripes of a single orientation. After many 36- to 48-hour sessions, my results showed a slight change toward the exposed orientation. I wrote up a manuscript on this and took it to Peter for his approval before submitting it for publication. He read it silently, smoking his pipe as I sat in his office, then crumpled it up and threw it in the trash can, saying “Michael, we don’t publish sh*t like this from my lab.” I left, but in the next few days, he told me all the things that were wrong with my experiment. In retrospect, I am grateful for having been prevented from publishing a bad paper with an incorrect result produced by wishful thinking, despite my strong belief at the time that I was being objective. In any case, it was clear that the quantitative measurements were needed.

I had the great good fortune to be joined in my thesis project by Helen Sherk, a brilliant student from a class a couple of years behind me. Once the quantitative system was working, Helen and I studied very young, visually inexperienced cats and found that the first neuron we recorded was perfectly selective for stimulus orientation, as were nearly all the others. So much for the idea that the organization of the visual cortex required visual experience. Still, our finding of innate selectivity made the Blakemore and Mitchell (1973) report that all neurons became selective for the orientation of stripes to which they were exposed even more exciting, for it indicated a dramatic plasticity. We repeated my earlier experiment using the objective measurement of responses after visual stimulation of anesthetized animals and saw no evidence of plasticity. Only then did we realize that we had to confirm the earlier report before trying to extend it. We replicated the striped cylinders and rearing procedure as closely as possible from the published reports and found no indication that the rearing had any effect when measured objectively. However, Helen realized that when the animals looked up and down, they were exposed to many orientations, so it seemed possible that our attempt at replication was flawed if our cats had looked up and down more than the ones in the original report. Our Science paper about this (Stryker and Sherk, 1975) caused great controversy: we seemed to be denying one of the most exciting findings in neuroscience, one that by this time had made it into most psychology textbooks.

The controversy had become transatlantic with the return of Blakemore to the mother ship of neuroscience, the Physiological Laboratory at the University of Cambridge. It was clear that our targeting of penetrations oblique to orientation columns and our objective measurement of responses were appropriate, but we had no way to ensure that something about the visual experience was different in our lab from that in the earlier report. We agreed on a collaboration in which the animals were reared in the Blakemore lab in England with exposure to either horizontal or vertical stripes and sent for recording at MIT, with the results to be presented at the next meeting of the Association for Research in Vision and Ophthalmology (ARVO). All of the visual cortex labs went to ARVO in those days, along with other vision scientists and ophthalmologists engaged in research. Helen and I recorded from the animals blind to their rearing conditions, and when the recordings from all the animals were finished and the data were in the computer and being printed out, we phoned Colin Blakemore to ask how each animal had been reared. He wouldn’t tell us. He wanted to know what the results from each animal were first. We ended the conversation feeling totally paranoid. Indeed, the collection of neurons from each animal had a slight bias toward one orientation or another, but it was no more than would be expected from a random sample from a normally reared cat. If, however, the slight biases were consistent with the rearing, the result would be taken as at least a weak confirmation of the Blakemore and Mitchell (1973) report.

We took our dilemma to Professor Emilio Bizzi, whom we regarded as fair and wise and whose own work was sufficiently distant from the visual cortex. Emilio made arrangements for an escrow procedure in which the results of our recordings and the English rearing were held both in Europe and the United States before being compared. As we suspected, the rearing had no effect on the orientation preferences of the visual cortical neurons. Indeed, the random biases were slightly in the opposite direction to the orientation exposed during rearing.

I went ahead with our agreed plan to present the results at ARVO and was surprised to find that our English collaborators were missing. To lighten the considerable tension in the audience, I had used black carpet tape to make a white shirt with vertical stripes on the front like those on many shirts, but with horizontal stripes on the back. I took care to keep my back away from the audience as I started my talk. After going through the rationale and the methods, I first showed the results from the animals exposed to vertical orientations—neurons with a wide range of preferred orientations, but slightly fewer for vertical than for others. I then said that now I would show the results for the animals exposed to horizontal contours and turned around as the next slide came up. The audience exploded in laughter, and I was happy that laughter rather than anger was the result of our clear failure to replicate the famous experiment.

The anger came later, and transatlantic mud was cast widely at my name. How could I make fun of such an issue? Our MIT department supported me and Helen fully, and the shouting eventually died down. We went on to publish our quantitative findings on the development of orientation selectivity without visual experience (Sherk and Stryker, 1976), which was just as Hubel and Wiesel had shown years earlier with hand plotting. We also then collaborated with Helmut Hirsch and Audi Leventhal on experiments in which visual experience was effectively restricted to contours of a single orientation by painting lines on goggles that were worn whenever the animals were not in darkness. There, the results showed a clear effect of the exposure, but it was a selective one (Stryker et al., 1978). Most neurons had become unresponsive or nonselective, and only one-sixth of the neurons were at all selective for orientation, almost all of those for the exposed orientation. In animals exposed to two different orientations, twice as many, about one-third, of the neurons were selective or weakly so, again nearly all of those for one or the other of the exposed orientations. These findings were consistent with the selective preservation of responsiveness in neurons that received stimulation that matched their innate orientation preference. I was disappointed that the entire edifice that my thesis had set out to extend—the beautiful idea that the cortex gets organized by experience—had crumbled. However, I had become notorious, for better or worse, and no one could criticize the technical advances we had made.

Postdoc at Harvard

At that point, I had become skilled at single-cell recording in both alert and anesthetized animals and in histology, and I was well educated in neuropsychology, neuropathology, psycholinguistics, the mathematics and statistics useful for neuroscience, and perception and psychophysics and its history. But I was largely ignorant of modern biology and had only an arcane view of cellular neurophysiology through the lens of Jerry Lettvin’s group, in which selective conduction failure at axonal branch points was thought to be as important as transmission at chemical synapses. I considered following Peter Schiller’s advice that I should take one of the faculty positions that was offered to me at the completion of my thesis rather than do a postdoc because I could pursue my own research and make short visits elsewhere to learn any new technique I needed. I had not applied for any postdocs when I went to give a lunchtime seminar at the Neurobiology Department at Harvard Medical School. Harvard Neurobiology was a completely closed society in those days and, while everything was shared within the department, no one outside it knew anything about what was going on until a publication appeared or a talk was given at a meeting. In a conversation with David Hubel and Torsten Wiesel later in the afternoon of my seminar, Torsten asked why I didn’t come to join their group as a postdoc for a couple of years. Deciding to do that was one of the best decisions I ever made.

The community at Harvard Neurobiology in those days was, in many respects, more like a commune than an academic department. Almost all of the eight or so faculty and all of the 15–20 graduate students and a similar number of postdocs ate lunch together every day, and every day there was a lunch talk, sometimes given by a visitor and more often by one of the participants. At the lunch talks, students and postdocs competed to raise the most devastating criticisms most quickly. It was said that one student’s criticisms kept a visitor from getting past his second slide, and when the visitor left the department that afternoon, he vowed never to darken its door again. The intensity was thrilling, and the group felt that it was creating the new neurobiology, combining biochemistry with biophysics, neuroanatomy, pharmacology, and what we now would call cellular and systems neuroscience. Most of postdocs and students cooked dinner there at least half of the nights and were in the lab seven days a week. The department taught a two-year course for its graduate students covering all of the topics just mentioned in successive semesters. A group consisting of most of the postdocs, about 12 of us, took each week’s syllabus and reading list from the graduate course as the basis for a weekly two- to three-hour meeting after supper. The postdocs were a terrific group trained in diverse labs, so there was genuine expertise in all of the subjects that we taught to one another. The intellectual ferment was further stoked by “evening meetings” every couple of months, for which the whole department would gather to listen to all of the members of one lab present its ongoing work to the entire group and receive suggestions and criticisms.

In the Hubel and Wiesel group, one of the big ideas, new at that time, was the combination of anatomy and physiology, exemplified by their demonstration with LeVay that projections from eye-specific layers of the lateral geniculate nucleus to the visual cortex matched its ocular dominance columns. We all collaborated with many of our colleagues on many different related projects. I was fortunate to work with Simon LeVay and Carla Shatz on anatomy-physiology projects involving ocular dominance plasticity, which prepared me for much of my later career (Shatz and Stryker, 1978; LeVay et al., 1978).

I was also lucky enough also to work closely with Hubel and Wiesel on a goal they had long sought—that is, determining the overall arrangement of cortical orientation columns. Louis Sokoloff at the NIH had pioneered the use of radiolabeled 2-deoxyglucose (2DG), a sugar that is incompletely metabolized by neurons and that accumulates in them at a rate proportional to metabolic activity. By closing one of the animal’s eyes and showing visual stimuli to the other after injecting 2DG, he had used it to reveal presumptive eye-specific layers in the lateral geniculate nucleus (LGN) and cortical ocular dominance columns. I was to visit Sokoloff to learn the technique, and Hubel and Wiesel and I would then use it to demonstrate orientation columns and make microelectrode recordings to verify what the labeling actually showed. Louis Sokoloff was a delight, taking great joy in taking me through the differential equations that modeled 2DG labeling on his new HP calculator.

When I returned to Boston, having mastered the technique, difficulties arose as we scheduled our first experiment. The neurophysiology tradition observed by Hubel and Wiesel, as well as by my doctoral program mentor Peter Schiller, was that no one put his name on a paper unless he or she had done a significant part of the experiment with his or her own hands. For example, Schiller’s name was not on any of my thesis papers. In later life, I tried to continue this tradition in my own lab, but eventually I was forced by grant reviewers to adopt the practice from biochemistry that was common in medical schools, in which the lab head’s name goes on everything even if his contributions are only financial support and criticism of the manuscript. The demonstration of the tangential organization of orientation columns was important to Hubel and Wiesel as a sort of capstone to their initial discovery of them, and they definitely wanted their names on the paper. But for them, this meant that they actually had to do the experiments with me. Torsten was the department chair, and frequently off to administrative meetings, and David traveled the world giving honorary lectures. The first experiment that would have all three of us in the lab for the entire day was six weeks hence. The next one after that was a month or two later, with similar intervals for subsequent experiments. After I had made and processed the tissue sections, I had to give them to David to reconstruct them in relation to our microelectrode penetrations. As a consequence, the work went much slower than it would have if I had been free to do these experiments myself, and with many fewer cases, but the Hubel, Wiesel, and Stryker (1977, 1978) papers really did have equal contributions from the three authors.

Teaching a Cold Spring Harbor summer course on techniques for studying the vertebrate central nervous system for two years with Carla Shatz and Peter Kirkwood was another formative experience. Getting to know this laboratory’s stellar group of molecular biologists and geneticists and discussing their work as we ate with them in the dining hall every day taught me an enormous amount about a wide spectrum of biology. Our course combined lectures by us and distinguished visitors with grueling laboratory experiments. During the first year, Francis Crick, who was just beginning to turn to neuroscience, sat in on many of the lectures, and we got to know him well.

One of the greatest influences on my later career was a three-month period in 1977 after Bill Harris arrived following his Caltech doctorate in Seymour Benzer’s fruit fly neurogenetics lab. Bill shared an office and lab with me. We spent many hours a day together trying to figure out what was the most important question in neuroscience that it might be possible to address. We actually hid out from Hubel and Wiesel, who seemed to us to become increasingly disappointed that we had no new experimental results and seemed to be worried that they had made a mistake in inviting us to join their group. Bill and I converged on a common question: what is the role of patterns of neural activity in guiding the development of precise connections in the brain? The next stages of both of our careers pursued this question with divergent approaches. Bill took advantage of genetics, and I took advantage of electrodes and pharmacology.

University of California, San Francisco

By my third postdoctoral year, I ached to have my own show, out from under the gaze of my Boston mentors. None of them thought that the research that I wanted to do, if I were to start my own lab at Harvard or MIT, was particularly interesting compared with what they thought I ought to do. My Harvard friends Zach Hall and fellow postdoc Louis Reichardt had gone to University of California, San Francisco (UCSF) in the previous two years, and while people in Boston found that incomprehensible, UCSF was beginning to become known for basic science, at least in molecular biology. In addition, it had the advantage of being 3,000 miles away from Boston. I was thrilled when they offered me a faculty position.

Arriving there, I found a social atmosphere that could not have been more different from Boston. People enjoyed life and did not feel that they had to be in the lab seven days a week when there was nothing that actually needed to be done on a Sunday. The faculty was egalitarian, with the labs of the assistant professors the same size as those of the senior faculty, and the important matters were discussed among the entire faculty. Intellectually, it was completely open and mutually supportive, with the basic scientists from all fields talking with one another about their best ideas, sharing reagents and equipment, and frequently collaborating. In and out of the laboratory San Francisco’s social atmosphere was liberating, in contrast to a much more class-bound society in Boston. One of the machinists in the department shop doubled his income by buying and selling modern art, and the telephone installer in the flat we rented invited us to his poetry reading on a weekend. Survival Research Laboratories made giant fire-breathing monsters that fought with one another on vacant lots, at least until the fire department arrived, and performances combining new theater, dance, poetry, music, and computer animation went on in the evenings. And I was the local expert on the visual cortex, free to do the experiments I wanted with no overlay of disapproval.

The neurobiology group was small, with most of its members from a single age-cohort: Zach Hall, Roger Nicoll, Mike Merzenich, Howard Fields, Mike Dennis, John Heuser, and Louis Reichardt were the younger members with appointments in the Physiology Department. Zach led the formation of an interdepartmental graduate program in neuroscience, which became our intellectual home. As a minor figure in the field, still in the shadow of its giants, I did not draw spectacular postdoctoral candidates for the first 12 years, and I recall advising one who did apply that he could do better—he should talk with Torsten Wiesel or David Hubel. But our neuroscience program drew amazing doctoral students, many of whom were drawn to my lab.

The Role of Neural Activity in the Formation and Plasticity of Ocular Dominance Columns

My main goal was the one set in the discussions with Bill Harris: to determine whether and, if so, how neural activity guided the development of connections. The half-millimeter size of the ocular dominance columns in the visual cortex of adult cats let us address this question anatomically as well as physiologically. My thinking was that events that actually take place at the scale of synapses, too small to be viewed except by electron microscopy, worked together to create these macroscopic structures. Our earlier work with LeVay had suggested that the projection from the retina to the LGN and on to the primary visual cortex was topographic, but that the inputs from the two eyes initially overlapped completely in the binocular zone (LeVay et al., 1978). In the hippocampus, the phenomenon of long-term potentiation (LTP) provided a mechanism for reinforcing connections that were simultaneously active. The development of ocular dominance columns in the input layer of the visual cortex could be explained if correlated activity drove the rearrangement of connections, and activity within each eye was better correlated than activity between the two eyes. I set out to test this idea in two ways: experimentally, by blocking activity in the two retinae pharmacologically during the time when eye-specific segregation was taking place in the cortex, and theoretically, after Ken Miller joined the lab following his training in theoretical physics. Both of these experiments took longer than was allowed before consideration of my promotion to tenure. But luckily, I also had taken on a few smaller projects that bore fruit more quickly, including a little Nature paper (Schoppman and Stryker, 1981), which gave my department the cover it needed to keep me around.

The experimental test of blocking the formation of ocular dominance columns by repeated infusion of tetrodotoxin (TTX) into the two eyes was a success at a coarse level, indicating that retinal activity was required. However, it was so difficult technically that it seemed too uncertain of success for a graduate student project, and further work on this project was carried out by me with a technician and later a talented mature research scientist. The publication of this work (Stryker and Harris, 1986) was delayed by several years for no good reason. It was complete by late 1983 but did not appear until 1986. Students now would never believe how slow and laborious it was to make perfect photographic prints in many copies and assemble them into montages for shipment to a journal, which would mail them out to reviewers. When things were lost in the mail, publication was delayed by an extra half year or more. After acceptance, a paper might not actually be published for an additional year.

I regard this paper as part of my most important contribution to neuroscience. Showing that activity was necessary for the formation of a pattern of orderly connections in the visual system that takes place prenatally in monkeys and humans established the principle that neural activity can play a role in development that is distinct from experience. Neuroscience had regarded the nature-versus-nurture or innate-versus-experiential question as being the same question as chemical specificity versus activity dependence. My experiments had provided evidence that retinal activity played a role in something that was clearly innate in other species, because visual experience is absent in utero. Later work provided numerous examples of experience affecting chemical signals for development. It seems obvious now that finding the mechanism—activity versus chemical specificity—does not answer the nature/nurture question, but it was not so at the time.

Preventing the formation of ocular dominance columns by retinal activity blockade did not show, however, what happened to the cortical arbor of individual LGN-cell axons. The next steps were very difficult and laborious experiments in which early retinal activity blockade using TTX (or control infusions that did not block activity) were combined with injections of tracers into the LGN that let us reconstruct entire axonal arbors that grew with or without retinal activity blockade (Antonini and Stryker, 1993a). Indeed the arbors were patchy, corresponding to ocular dominance columns when there was normal retinal activity, and continuous when activity was blocked. We used the same approach to examine what happened to these geniculocortical inputs when occluding the vision of one eye during the critical period caused its ocular dominance columns to shrink, and we found that arbors serving the deprived eye lost half of their extent and at least half of their synaptic boutons in less than a week (Antonini and Stryker, 1993b).

The activity blockade experiments also did not establish that it was the pattern of activity rather than its amount that mattered. To address that question, I tried an even more difficult experiment—blocking all naturally occurring retinal activity with TTX and introducing controlled patterns of activity by stimulating the two optic nerves alternately through separate electrodes or by stimulating them simultaneously through an optic tract electrode. The assays of the effect of the different patterns of activity were both physiological and anatomical: microelectrode recording of ocular dominance along penetrations that would cut across many ocular dominance columns, if they were present, and transneuronal tracing of the anatomical projection from one eye through the LGN to the cortex. The results of the physiological assay were clear. Alternate stimulation allowed ocular dominance columns to form and enabled cells dominated by one eye to be clustered together, alternating with clusters dominated by the other. Simultaneous stimulation, in contrast, left nearly all of the cells responsive to both eyes, with no evidence of clustering according to eye dominance, which was exactly the same as if there were no activity at all. The anatomical tracing experiments were mostly marred by various artifacts, and only a few provided interpretable results, all of which were consistent with the physiology.

I presented the preliminary results of these experiments at various meetings, with the reports appearing in books (Stryker, 1986, 1989), but I refrained from submitting a paper that I regarded at the time as a magnum opus in the hope that I could improve the anatomical tracing. Eventually I gave up, and I have regretted ever since that I did not publish a real paper on this work that had consumed so much of my effort over the years. The advice I give to young colleagues and have mostly followed myself since that time is that it is self-destructive to let the perfect be the enemy of the good. If you have sound, important findings and can’t do the ideal experiment to confirm or extend them after a year or two, then publish what you have and move on. Perhaps it won’t be a cover story in Science, but you owe it to the field and to the institutions that supported the work to put it into the literature where it will be seen, and maybe someone cleverer than you will take the next step.

The theoretical work on ocular dominance column development was made possible by Ken Miller’s joining the lab for his doctoral research. I had played for some years with crude computer simulations of activity-dependent development, and several simulations had appeared in the literature. The trouble with all of the computer simulations was that they were no more enlightening about mechanism than watching biological development itself, and they had so many parameters that simulations could never explore all of the relevant parameter space. The problem that Ken took on was to determine what factor—the size of the afferent arbors, the degree of correlated activity, the properties of the synaptic plasticity rule, or the spread of excitation and inhibition in the cortex—is responsible for determining the spacing of ocular dominance columns. I insisted on a model in which all the parameters and the outcomes could at least in principle be measured in feasible experiments so that our model would have a genuine, quantitative connection with biological reality. Ken had acquired an appreciation of what kinds of features could reliably be measured because I had him carry out a neurophysiology experiment as part of his doctoral training (Miller et al., 1989). We hoped to solve the problem of ocular dominance column development analytically, so that we could appreciate the role of each factor through its contribution to an equation.

To work on this problem, we used the San Diego Supercomputer Center to run simulations, but Ken persisted in trying to derive an analytic solution to the most important limiting cases. My education in mathematics was finally useful in allowing me to understand the progress that Ken was making. We talked with several mathematicians, including ones who worked on computational fluids, which can form periodic patterns, but the crucial help at several points came from the late Joseph B. Keller, a wonderful, modest mathematician at Stanford whose stature in the field I did not appreciate until, during the time he was helping us, I saw his picture in the newspaper getting the National Medal of Science. The Miller, Keller, and Stryker (1989) Science article was the first model of such a complex phenomenon in brain development in which the roles of each factor could be understood in the form of equations. The understanding resulting from this model guided much of my work for the next decade.

Michael Merzenich and Adult Cortical Plasticity

My laboratory was located adjacent to that of Michael Merzenich, whose main activity at the time I arrived at UCSF was doing the basic science for the cochlear electrical stimulation prosthesis for profoundly deaf people. The inability of the cochlear prosthesis to reproduce the normal pattern of activity in the eighth nerve, in combination with its remarkable success at restoring high levels of speech perception in patients, convinced Mike that the brain of normal adult humans was remarkably plastic. Mike had been Vernon Mountcastle’s graduate student working on somatosensory physiology for his doctorate. Not long after I arrived at UCSF, Mike returned to somatic sensation during a sabbatical at Vanderbilt with his old friend from postdoctoral years, John Kaas. Their work with students revealed dramatic plasticity of the topographic maps in somatosensory cortex following partial peripheral deafferentation. I was very skeptical about large-scale plasticity in primary cortical areas of the adult brain. After Mike returned from sabbatical, he and I worked together every Monday on somatosensory cortical plasticity, which we studied with high-resolution microelectrode mapping, making about 300 microelectrode penetrations over 12 hours in each session, before and at intervals of weeks after peripheral or cortical lesions (Merzenich et al., 1984; Stryker et al., 1987). The adult plasticity was clearly genuine.

For several years, until my own lab’s work on the visual cortex kept me from taking Mondays off, this collaboration was as stimulating as it was arduous and was a forum for a continuing argument between us that we sought to resolve by planning experiments. I poo-pooed the modest plasticity he and I had found in the adult brain in contrast to the dramatic effects of manipulations early in development. Mike countered that adult plasticity could be much greater than we had found to date, and that in any case, our research had to be directed toward changes that could be induced after early development if our work was to do any good uncovering potential therapies for human patients. I thought that the next step in this research should be to understand the anatomical basis of the reorganization of cortical maps that we found. Mike, in contrast, thought that it was most important to discover factors that promoted the induction of this plasticity, by doing experiments using behavior to manipulate neural activity and attention and using pharmacology to manipulate neuromodulators. As it has turned out, Mike’s approach has been fruitful and has led to useful therapies. But we still don’t know the anatomical or neural circuit basis of most of the phenomena of adult cortical plasticity, and we ultimately will need to do so. Perhaps ironically, much of the current work in my laboratory is focused on mechanisms of adult plasticity in the visual cortex.

This long-lasting debate with one of my closest friends and most respected colleagues has been a highlight of my intellectual life. We differ in background, approach, and style but agree on what constitutes a good experiment and the value of trying to carry it out.

Ferrets

Many of the events I wished to study, such as the emergence of visual cortical orientation selectivity, began soon after birth in the cat, and neonatal kittens were fragile experimental subjects. Ferrets, which the Guillery laboratory had studied anatomically and found to have a typical carnivore LGN and visual cortex, resembled long, skinny cats. The exciting thing about the ferret was that its brain appeared to develop at the same pace as the cat’s, but it was born two weeks earlier with its visual system like that of a two-weeks prenatal cat. My initial hope was to study events like the origin of orientation selectivity that were neonatal in the cat in a hardy two-week-old ferret. I also hoped to study other events that were prenatal in the cat, such as the role of neural activity in the segregation of inputs from the two eyes into different layers of the LGN. While no one had ever recorded from the visual system of the ferret, I was confident that in a couple of years, we could repeat in the ferret every important experiment that had been done on the organization and development of cat’s visual system.

My first graduate student, Kathleen Zahs, took on the task of characterizing the visual system of the ferret so that we could begin to use it for studies of development and plasticity (Zahs and Stryker, 1985). We first studied the LGN and found the properties of the neurons very similar to those in the cat, as we had hoped, but with a clearer distinction between the brisk (X- and Y-like) and sluggish (W-like) responses. Guillery had pointed out a pair of sublaminae (“leaflets”) in each of the main layers of the LGN. For no good reason, I was certain that these sublaminae would correspond to a division between X-like linear inputs and Y-like nonlinear inputs from the retina. We made recordings from a number of ferrets to study the linearity of their responses and failed to see the difference between the leaflets. For months, through many experiments, we missed the obvious function of this subdivision, despite its being clear without exception in our data and despite hearing from McConnell and LeVay (as we were doing our experiments) that in the mink, a closely related carnivore, the leaflets reflected a segregation of on-center and off-center retinal inputs (Stryker and Zahs, 1983). This episode has stood out in my mind ever since as a warning about the potential danger of hypothesis-driven research and the need to look at all features of the data as they come in. If the hypotheses are too narrow, it is possible to miss the obvious.

After we knew the basic organization of the ferret visual system from Kathy’s work, another wonderful student, Barbara Chapman, joined me and Kathy in an attempt to use physiology to confirm or refute the anatomical hypothesis of Hubel and Wiesel on the origin of orientation selectivity in visual cortex. Was it the result of convergence of input onto simple cortical cells from geniculate cells whose receptive fields lay along a line in the visual field? We measured the preferred orientation of one cortical column and then silenced the cortical cells pharmacologically so that we could record the tiny spikes produced by the cortical arbors of geniculate cells. In most cases, the receptive fields of these arbors were precisely aligned with the preferred orientation of the cortical cells (Chapman et al., 1991), providing strong confirmation of Hubel and Wiesel’s hypothesis. Ed Ruthazer, another wonderful student, showed that the formation of patchy clustered corticocortical connections first emerged just before orientation selectivity began to develop and became prominent at the same time as mature selectivity was beginning. Neural activity was absolutely necessary for this development (Ruthazer and Stryker, 1996). The results indicated that the anatomical specificity of long-range horizontal connections in the visual cortex results from an activity-dependent process that initially can use spontaneous activity in the cortical and thalamic networks to establish crude periodic connections and that later uses visual cues to refine these connections.

Barbara Chapman then investigated the role of neural activity in the development of orientation selectivity, half of my original reason for adopting the ferret. She found that neural activity in the visual cortex was absolutely necessary for orientation selectivity to develop at all beyond its infantile state, which we believed might result from random connectivity (Chapman and Stryker, 1993). Visual experience was also necessary for fully normal development, but orientation selectivity developed to some extent even in animals in which vision was compromised by eyelid suture. Her findings raised the question of whether the primitive orientation selectivity we saw initially was the seed for normal development, or whether the adult orientation selectivity developed independently of its initial activity-independent state. Pursuing this question gave rise to another delightful collaboration with Tobias Bonhoeffer. Partly in San Francisco and then at the Max Planck Institutes in Frankfurt and Munich-Martinsreid, the three of us worked together to use intrinsic signal optical imaging to look at the pattern of orientation columns in ferret visual cortex as it first emerged and then matured, tracking development in individual ferrets (Chapman et al., 1996). Surprisingly, the pattern of orientation columns was stable after even the first initial hints of its appearance, at an age when Barbara’s earlier microelectrode recordings had shown only slight selectivity. This finding was consistent with Ruthazer’s anatomical experiments in suggesting that intracortical connections played a stabilizing role. Barbara stayed in Germany to finish our joint experiments after I had to return to San Francisco to teach, and she and Tobias completed additional experiments for another interesting paper. The friendships made working together night and day are lifelong.

Another motive for turning to ferrets was to determine whether neural activity was responsible for the segregation of eye-specific layers in the LGN. The layers formed very early in development, and I tried for many months to create the technology to carry out this experiment in baby ferrets. Taking the next step toward solving this problem reactivated an old collaboration with Carla Shatz, who had been a friend since Boston days and who had moved to Stanford at the time I went to UCSF. Carla had become expert at prenatal surgery for her studies of retinogeniculate innervation. We worked together to equip fetal cats with what looked like a scuba tank but was really an osmotic minipump that delivered TTX to the LGN to block activity during the two weeks encompassing retinal innervation and layer formation. Tracing retinal inputs after this treatment revealed no indication of the eye-specific layers that would normally be present, but retinotopy appeared to be preserved (Shatz and Stryker, 1988). Our result was interpretable only if there actually had been spontaneous activity in the developing visual system for the TTX to block, but we had no evidence that there was any. We reported our finding in the same issue of Science in which Lucia Galli and Lamberto Maffei revealed that there was clear periodic activity in centrally projecting retinal ganglion cells in fetal rats at a comparable stage of development (Galli and Maffei, 1988). The two papers together provided strong support for a role for spontaneous retinal activity in organizing central connections.

The final chapter in the story of the formation of eye-specific layers in the LGN was not written until much later. Torrealba and co-workers had shown earlier that there were multiple topographic maps in the optic tract that appeared to reflect the temporal order in which different retinal ganglion cells grew. It appeared possible that the earliest inputs, from the contralateral eye, reached the innermost border of the LGN first and remained there, forming an eye-specific layer, with the later-arriving inputs forming additional layers. Much later, in her independent lab, Barbara and co-workers showed that transiently blocking retinal activity until inputs from both eyes had reached the LGN removed the advantage of the early arriving inputs. When activity was then restored, the laminae formed in a process requiring activity, but their arrangement was random (Huberman et al., 2002).

Institutional Engagement at UCSF

From the time of my arrival at UCSF, I was happy to contribute to the institution and did so in many ways. I was active in graduate program teaching and did not shirk search committees or other somewhat-optional features of academic life. When Zach Hall became physiology chair, I became co-director of the neuroscience program together with Louis Reichardt, as well as vice chair of the department. While I was generally very happy at UCSF, I found it hard in 1993 to resist the temptation to leave UCSF for additional desperately needed lab space and the ability to move to an even more desperately needed bigger house, as my family had grown. A commitment from the chancellor that my needs would be met in San Francisco allowed me to remain, and part of the reason I was happy to remain was that I had the perfect department chair, giving me all the influence I wanted over our affairs with almost none of the work. I was blindsided a few months later when Zach moved to the NIH to become director of National Institute of Neurological Disorders and Stroke. The dean called me into his office and told me “Michael, you have to step up to the plate.” I was happy to chair the department for the next 10 years, and it ended up being 12 years before I was allowed finally to return full time to my lab. I took enormous pleasure and pride in recruiting terrific young scientists to UCSF and in helping them become successful.

Other activities outside the lab were also exciting. Essentially without informing the central administration, a group of faculty involved in graduate education, led by J. Michael Bishop, created the UCSF Program in Biological Sciences (PIBS), which encompassed graduate programs over a wide range of biology from biophysics through molecular biology and genetics to cell and developmental biology and neuroscience. PIBS changed the course of graduate education by moving it out of the departments and putting stipend support in the hands of the students, who became free to work with any of the PIBS faculty members. It also revolutionized faculty recruitment by making it possible for basic scientists in clinical departments to become first-class citizens with access to all of the resources, including graduate students and postdoctoral support, that were available to their basic science colleagues so long as they were recruited through search committees dominated by PIBS. Helping to create PIBS and directing it for two years while Mike Bishop was away was a source of great satisfaction.

Closer to home, the campus supported our approach to the Keck Foundation to renovate a 10,000-square-foot floor of the laboratory building in which we were housed to create the Keck Center for Integrative Neuroscience. While it seemed too little space for a group our size, its crowding of the labs for eight terrific systems neuroscientists cheek by jowl gave rise to an unprecedented level of interaction that was almost entirely positive. Led by my friend Steve Lisberger, our center was the only medical school chosen by the Sloan Foundation to host one of its centers for theoretical neuroscience despite our lacking a mathematics, physics, or computer science department. Having worked with Chuck Stevens to get the Sloan Foundation engaged in supporting theoretical neuroscience by organizing summer workshops at the Santa Fe Institute, I was especially pleased that we were granted a Sloan Center.

I also was one of the leaders of the early planning for our new campus at Mission Bay, including visiting UC Regents in their homes and workplaces to help get our plan for its construction approved. The new campus was the key to converting a wasteland into what has now become a vital part of our city. I still have my hard hat and shovel from the groundbreaking for the first building.

Surprisingly, the years as department chair, an activity that consumed nearly half my energy, were among the most successful for my lab, with amazing students who did some of the best work the lab has ever done. While they mostly started in the lab before I became chair, their success is probably due to their being freed from detailed oversight by my being too busy with administration. I also think that the lab’s success was possible because Dr. Antonella Antonini, formerly a professor in Verona, Italy, joined as a research scientist. Having a brilliant, mature, scholarly scientist in the lab every day supplied a needed degree of knowledge and stability.

Ocular Dominance Columns

As new approaches became possible, I kept returning to the questions surrounding the roles of experience and neural activity in the development and plasticity of cortical columns in the cat, and we made numerous discoveries. Postdoctoral fellow Yoshio Hata showed anatomically that the plasticity of ocular dominance columns was reversed when the visual cortex was inhibited by infusion of muscimol during monocular visual deprivation during the critical period (Hata and Stryker, 1994), and student Takao Hensch showed that the spacing of developing ocular dominance columns could be regulated up or down by increasing or decreasing GABAA-mediated inhibition during their development (Hensch and Stryker, 2004). Postdoctoral fellow Mike Crair showed that visual experience was necessary for the emergence of strong ipsilateral-eye responses at the onset of the critical period and that development was independent of visual experience before that time (Crair et al., 1998). Abruptly at the onset of the critical period, selective cortical responses fell apart in binocularly deprived animals but increased slightly with normal vision. In the course of these experiments, we improved the sensitivity of an anatomical tracing technique and discovered that an aspect of ocular dominance column development took place a week earlier than reported in one of my earlier papers. I definitely wanted to report it before anyone else, and I have never been so eager to get a new finding published quickly (Crair et al., 2001).

I was powerfully struck by the findings of experiments with postdoctoral fellow Josh Trachtenberg, who discovered that the time course of the effects of monocular deprivation during the critical period were much slower in the input layer (layer 4) than in the cortical layers above and below, where dramatic plasticity took only a day or two (Trachtenberg et al., 2000). Anatomical connections among neurons in layer 3 showed half-millimeter scale rearrangements in 24 to 28 hours, matching the rapid change in responses (Trachtenberg and Stryker, 2001). The slower plasticity in layer 4 appeared consistent with the time course of plasticity in its input from the LGN.

Despite this progress, I became discouraged that we would ever be able to figure out the mechanisms of plasticity with the approaches available in cats and ferrets. Our work had produced a lovely story about neural activity and visual experience in the development and plasticity of the visual cortex that had become part of the textbooks and had some clinical relevance, with lots of interesting phenomena and models that could make sense of them. But in the end, these discoveries were at a level above that at which things actually happened in the brain. I feared that I would end my career with hand-waving. I needed another problem that would excite me.

The inferotemporal lobe representations of complex objects had intrigued me since the early reports of Charlie Gross. Studying this problem in monkeys and with human psychophysics was an exciting prospect. I followed the pioneering work from the Tanaka and Miyashita laboratories, wrote some News and Views pieces about it (Stryker, 1991, 1992), and prepared myself to abandon carnivores and development and turn to object perception in monkeys. This might have been a fruitful path to follow, as the work of Doris Tsao and other labs have shown. Indeed, I would have done so but for the next development.

Mutant Mice

Josh Gordon came to the UCSF medical doctor/doctoral program intending to study tumor viruses in Mike Bishop’s lab. He took our introductory course in neuroscience, and because we had started PIBS, he was able to do a rotation and then join my laboratory. He joined it on the condition that we would begin to study genetically manipulated mice as an approach toward understanding the mechanisms of development and plasticity. I had been interested in doing this for some years, given that recombinant DNA made it possible to make mice in which interesting signaling systems were mutated. But mice were a big change, and I knew that my vision friends would tease me by singing “Three Blind Mice” if we were to switch. Josh’s enthusiasm for this approach pushed me over the edge. Transgenic mice opened promising new approaches to understanding how the brain wires itself and adapts to experience.

The anatomy and physiology of the mouse central visual system had, of course, been studied 20 years earlier in pioneering work focused on the consequences of spontaneous neurological mutants maintained at Jackson Labs. The beautiful work by Ursula Dräger and David Hubel and by Alan Perlman’s group on the visual cortex of the reeler mouse, in which cortical lamination is turned upside down, led to powerful conclusions, but hoping for additional spontaneous mutations was not a promising way to follow it up. These groups had solved, however, some of the problems of mouse anesthesia consistent with strong responses of neurons in the visual cortex.

Josh and I first worked on the mouse preparation to make visual cortex and LGN responses reliable. He then did the research that resulted in the foundational paper for our studies, and many other studies, of visual cortical plasticity in mice (Gordon and Stryker, 1996). He found that the mouse visual cortex indeed had rapid activity-dependent plasticity in response to monocular visual deprivation within a well-defined critical period peaking at four weeks of age. This finding set the stage for a huge number of experiments, many by my lab, delineating the signaling systems responsible for this form of plasticity (e.g., Gordon et al., 1996). I didn’t know whether Josh was excessively brave or merely foolhardy in his choice of a residency in psychiatry rather than in neurology or ophthalmology, where I was sure he would become a leader of his field. He told me he was not afraid to do something hard and that the experience in my lab was preparation for working on the most important problems of the brain.

Together with Michela Fagiolini, a new postdoctoral fellow whose doctoral degree was from the Maffei laboratory in Pisa, Antonella Antonini did foundational anatomical work on mouse visual cortex and on the changes in thalamocortical axons produced by monocular visual deprivation (Antonini et al., 1999), as she had done earlier with cats.

Takao Hensch came to do doctoral work in my lab after a postgraduate fellowship year with Masao Ito in Tokyo and Melitta Schachner and Wolf Singer in Germany. He was obviously brilliant, thoughtful, and careful. He always prepared thoroughly for experiments, and no one else in my lab has done as few unproductive ones. His joining my lab did wonders for my reputation in Asia and Europe. Takao started working on plasticity in cats, using cortical brain slice recordings to verify the actions of drugs we used to manipulate signaling and activity in the visual cortex (Hensch and Stryker, 1996). After collaborating with Josh on mutations of enzymes involved in excitatory transmission that altered critical period plasticity, he began work that has turned out to be tremendously interesting and important. A colleague in the Diabetes Center had mutated Gad2, one of the two enzymes responsible for synthesis of the inhibitory neurotransmitter, GABA. Its diabetes phenotype did not look very interesting, but the mice were fairly healthy. Hearing about this mutant, we realized that it might give us a means of studying the role of synaptic inhibition in cortical plasticity. Our colleagues were happy for us to have the mouse in the hope that we would find something interesting, with the proviso that they would publish the basic description of the mutant first.

Around the same time, another student in the lab, Jessica Hanover, had collaborated with Josh Huang in the Tonegawa lab on mice that constitutively overexpressed brain-derived neurotrophic factor (BDNF) and discovered that these mice have a precocious critical period by one week (Hanover et al., 1999). Josh Huang found that they also had a similarly precocious development of cortical inhibitory interneurons, so it was reasonable to speculate that the maturation of inhibition triggered or gated the critical period of plasticity, although this of course was only one interpretation among the many possible.

Takao found that the Gad2-deficient mice did not have a critical period (Hensch et al., 1998). Monocular visual deprivation simply did not cause the cortex to become less responsive to the deprived eye either at the normal time or earlier or later. While this by itself was somewhat interesting, the entire mouse lacked Gad2, so it provided little evidence specifically about cortical inhibition. The important experiment was to determine whether we could rescue plasticity by a purely cortical manipulation. As it turns out, diazepam (valium) was an ideal reagent. It acts postsynaptically on GABA receptors to double their open time, essentially producing twice as much inhibition for each inhibitory action potential. We imagined that our having gotten rid of one of the two GABA-synthesizing enzymes would cut GABA release in half (an assumption later verified using in vivo micro-dialysis in Takao’s independent lab), so diazepam ought to restore a normal amount of inhibition. Applying diazepam specifically to a small region of visual cortex in the Gad2-mutant mice during visual deprivation produced a normal critical period, providing powerful evidence that the level of intracortical inhibition is an essential trigger for critical-period plasticity.

This discovery was the basis of the early phase of Takao’s independent career, first in his own lab at RIKEN in Japan (skipping a postdoc) and later at Harvard, during which he found out a great deal about the factors that regulate activity-dependent plasticity. Unfortunately for me but great for them, my terrific postdoc Michela Fagiolini and Takao fell in love so that she left to be with him in Japan before she could complete her main projects in my lab. Their three beautiful children are now in high school and college, and both she and Takao are doing great work in their labs at Harvard, so in their case, all is well that ends well. I will never forget my conversation with Michela that failed to persuade her to stay in my lab for another year and finish projects that would have enhanced her reputation: She tapped her fist on her chest and said, “But the heart, Michael; but the heart.”

A technique that greatly advanced our work on visual cortical plasticity was the work of one of the trainees in our Sloan Center for Theoretical Neuroscience, the goal of which was to bring scientists trained in a hard, theoretically grounded science such as mathematics and physics into neuroscience, either to become neurobiologists or else theoreticians who, unlike most, actually would understand the neurobiology about which they were theorizing. Valery Kalatsky, a physicist trained in Russia and Texas, joined my lab. We had used images of an intrinsic optical signal associated with brain metabolism to view the patterns of activity elicited by different visual stimuli in cats and ferrets for many years. It had been taught to me by its inventor, Amiram Grivald, over a visit to his laboratory at the Rockefeller (in Torsten Wiesel’s group there) where I got to know their postdoc Tobias Bonhoeffer. The intrinsic signal was tiny, a fractional change in reflectance of at most a few parts in 10,000. While it was also present in mice, we found it too small and too variable to be of use for quantitative study of such a small brain. Val Kalatsky and I thought of a way to measure it much more precisely by imaging it over repeated stimulus cycles and analyzing the component of the signal at the frequency of stimulation, similar to the way that Tony Norcia was able to measure visual evoked potentials in babies who attended to the stimulus screen only briefly (Norcia and Tyler, 1985). This approach was successful, allowing reproducible measurement of response strength as well as the construction of high-resolution topographic maps (Kalatsky and Stryker, 2003). It had the advantage that it is almost completely noninvasive—light is the only thing that enters the brain—and could be measured accurately through an intact skull.

Megumi Kaneko, who trained as an anesthesiologist in Japan but abandoned clinical work to do doctoral work in neurobiology, took great advantage of intrinsic signal imaging for our studies of ocular dominance plasticity after she joined the laboratory as a postdoctoral fellow. She first did a series of more than 40 wild-type mice to evaluate the stability of the magnitudes of the intrinsic signal responses in visual cortex to the two eyes. She found them to be remarkably stable, neither eye’s response fluctuating more than 10% from day to day. The relative cortical responses to stimulation of the two eyes in the binocular segment of the visual field was exactly what would be expected from microelectrode recordings of a population of single neurons in the binocular zone of the visual cortex.

Megumi tracked the changes in response over the course of monocular deprivation during the critical period and found an initial dramatic decrease in response to the deprived eye for the first two to three days while the response to the open eye remained stable. As deprivation continued for an additional two to three days, the response to the open eye became much stronger in a second phase of plasticity, and surprisingly, the response to the deprived eye also increased to some extent. Finally, when the deprived eye was reopened during the critical period, responses in both eyes returned to their original levels (Kaneko et al., 2008a; Kaneko et al., 2008b). We knew that N-methyl-D-aspartate (NMDA) receptors were implicated in at least the first phase because of its blockade by even low doses of the NMDA-receptor blocker CPP. But what accounted for the later phases? The Malenka lab had found a phenomenon of homeostatic synaptic scaling in hippocampal slices and cultures that was dependent on tumor necrosis factor alpha (TNFα) signaling and was prevented by null mutations of TNFα or pharmacological depletion of TNFα (Stellwagen and Malenka, 2006). It seemed possible that cortical activity was sufficiently depressed after the first phase of plasticity produced by monocular deprivation for homeostatic synaptic scaling to be the cause of the second phase. Indeed, the open-eye responses never increased in TNFα mutants or when TNFα signaling was blocked pharmacologically (Kaneko et al., 2008b). These experiments established homeostatic synaptic scaling as the basis for the second phase of ocular dominance plasticity.

Earlier work on cats from the labs of Wolf Singer and Carla Shatz and my own lab had suggested that ocular dominance plasticity might result from a competition for limiting quantities of brain-derived neurotrophic factor (BDNF), although my lab’s later findings indicated that our interpretations of these pharmacological experiments were misleading (Gillespie et al., 2000). BDNF was known, however, to be released in response to neural activity in some circumstances. Our UCSF colleagues Kevan Shokat and Pam England had come up with a perfectly selective and effective chemogenetic means of blocking signaling of the BDNF receptor, TrkB, in mice. Megumi used this approach to do experiments that showed, surprisingly, that blocking TrkB had no effect on either the initial or second phase of ocular dominance plasticity, conclusively refuting the earlier hypothesis about competition for BDNF. However, blocking TrkB completely prevented the third phase, the recovery of responses after reopening the deprived eye, as well as the reduction in open-eye responses that normally accompanies it (Kaneko et al., 2008a). This finding was consistent with the recovery of deprived-eye responses being mediated by the formation of new synaptic connections (or the expansion of existing ones) because of the known requirement for BDNF-TrkB signaling for the formation of new synapses in neuronal cultures.

These two experiments gave us an anatomical hypothesis for the substrate of ocular dominance plasticity: the loss of deprived-eye synapses in phase 1, the preservation of synapses in phase 2 with a homeostatic increase in their strength, and the regrowth of deprived-eye synapses in phase 3 after reopening the eye. Only recently have we been able to provide anatomical evidence for this hypothesis by tracking the dendritic spines and axonal boutons of layer 2/3 cells using 2-photon microscopy (Sun et al., 2019).

Map Formation and Organizing Connections Between Visual Areas

After our experiments on ocular dominance columns convinced me that spontaneous neural activity could guide the wiring of neural connections in development, I wondered whether neural activity guided the formation of precise topographic maps, a process that is innate in the sense that it develops early and does not depend on experience. A large part of the reason for turning to ferrets was the hope that I could use them to study map formation in the visual system. But try as I did for years, I had made no progress on this problem in ferrets. In the meantime, compelling experiments on gradients of ephrins and eph-receptors seemed to indicate that the problem of map formation was solved and that it was all due to chemospecificity—not lock and key, as Sperry had proposed, but gradient matching. But most of this work had been done on the superior colliculus (a.k.a. optic tectum) or, to a limited extent, in the LGN, both of which receive direct retinal input, and it was not known whether a similar mechanism operated in the cortex.

An amazingly talented postdoctoral fellow, Jianhua Cang (JC), joined the lab and began to work on this project, on which we sought out and found the perfect collaborator: David Feldheim at the University of California, Santa Cruz, 90 minutes south of UCSF. Dave was an expert in eph/ephrin signaling and not only had mutant mice but also had histochemical reagents that revealed eph/ephrin protein distributions. Dave’s lab found that there were gradients in the primary visual cortex of ephrin-A2, A3, and A5, so JC studied the null mutants of each one by using intrinsic signal imaging to reveal the topographic maps in visual cortex and by tracing the precision of anatomical projections from the LGN to V1. The results were disappointing at first because no phenotype was evident in any of the mutants. Dave pointed out that eph/ephrin binding is fairly promiscuous, so we then tried all the double mutants, without finding any effect. At long last, after Dave was able to make mice with the triple knockout of all three ephrin-As, JC found the cortical map of azimuth to shrink and to become rotated, displaced, and far less precise. Of course, the entire mouse carried the mutation, so these findings did not prove that the ephrin signaling defect was in the cortex. Using in utero electroporation to misexpress ephrin-A5 in the cortex at a time before map formation, Megumi Kaneko shifted the map when the extra ephrin was to one side of V1 and disorganized it when in the middle. These experiments demonstrated that specific eph-A/ephrin-A signaling guides map formation in the visual cortex (Cang et al., 2008).

We next turned to the role of neural activity. Markus Meister and Rachel Wong in the laboratories of Dennis Baylor and Carla Shatz at Stanford had extended the earlier findings of Galli and Maffei by showing that apparently random waves of spontaneous activity propagated across the retina and drove the ganglion cells during the period that map formation was taking place, long before the retinal ganglion cells responded to stimulation of the photoreceptors (Meister et al., 1991). This was the ideal pattern of activity for driving map formation in models. The retinal waves during the first postnatal week were driven by nicotinic cholinergic signaling, and a cholinergic receptor mutation disrupted the organization of the waves but did not block activity (McLaughlin et al., 2003). JC studied these mutant mice and found that maps of azimuth in visual cortex and the anatomical projection from the LGN to visual cortex were indeed very much less precise than normal (Cang et al., 2005). Again, we had to confront the issue that always makes interpretation of mutant animals difficult. In this case, there is cholinergic signaling in the visual cortex, so the effect of the mutation might not be the product of its disruption of retinal activity but instead a direct action on cortex. Collaborating with my colleague David Copenhagen’s laboratory, we showed that a drug delivered only to the retina of wild-type mice during the first week of development copied the effect of mutation on neural activity; JC found that the drug also reproduced the mutation’s effects on the cortical map.

At this point, we had proved that both patterned retinal activity and ephrin-A signaling were important for cortical map formation, but were they the whole explanation? With the Feldheim lab again, we disrupted both retinal activity and ephrin-A signaling and completely prevented the formation of the map of azimuth (Cang et al., 2008b). Surprisingly, the map of elevation was almost intact, a topic for future study. In the superior colliculus as well, the same factors as in visual cortex were responsible for map formation (Cang et al., 2008a), but it appeared that the timing was slightly different, with the effects of ephrin signaling operating somewhat earlier than those of retinal activity.

Layer 5 cells in the visual cortex project to the superior colliculus, and the map of the cortical projection is perfectly aligned with that of the direct retinal input to the colliculus. We took advantage of a mouse that the Lemke laboratory had created by ectopically expressing an Eph receptor in half the retinal ganglion cells, producing a duplicated map of azimuth in the superior colliculus but (for reasons now understood but too long to explain here) only a normal single map in visual cortex. The superior colliculus also has a normal single gradient of ephrin signaling. When activity is disrupted, we found that the cortical projection to the colliculus looks normal, forming a single map. When retinal activity is present, the corticocolliclular projection, which develops later than the direct retinal projection to the superior colliculus, aligns itself with the retinal input, forming a duplicated map. This indicates that correlated activity can override the chemical gradients in the development of precise connections between these two areas (Triplett et al., 2009).

Our last paper on map formation is one the papers that I am most proud of. My doctoral student Melinda Owens joined Dave Feldheim and his former postdoc Jason Triplett, by then in his independent lab, to study the interaction between neural activity and the chemical gradient in more detail. Using the Lemke mouse that makes a duplicated map in the superior colliculus, we asked what happens if the strength of the ephrin gradient for map formation is made weaker so that it is comparable to the effect of the structured neural activity. We found that when the mice had half the level of ectopic Eph expression in one population of ganglion cells, map formation was clearly stochastic: sometimes duplicated, sometime single, and sometimes different between the two hemispheres or between the lateral and medial portions of one superior colliculus (Owens et al., 2015). A computer model of map formation as a stochastic process influenced by both neural activity and chemical gradient exactly reproduced these findings, showing the same variability when the two factors were equal in strength. These results were a culmination of our work on the formation of retinotopic maps, a process that I believed we had fully explained, and I felt ready to retire the problem. No other episode in my life as a scientist has been more satisfying or has had more wonderful co-workers.

Neural Transplantation to Induce Juvenile Plasticity in Adult Mice

One conclusion that had emerged from our studies of development and plasticity during the critical period in early life was the crucial role of cortical inhibition in triggering plasticity. Two UCSF friends and colleagues, Arturo Alvarez-Buylla and John Rubenstein, had studied the development of inhibitory interneurons and their long tangential migration from the site at which they were generated in the ganglionic eminences into the developing neocortex. My postdoc Sunil Gandhi and Arturo’s medical doctor/doctoral student Derek Southwell came up with a wild speculation: Would embryonic inhibitory neurons trigger plasticity if they were transplanted into mature cortex? Arturo and I went along with their idea because we were confident that both of them would have other experiments that could be counted on to be productive if this one failed. We knew that the normal critical period peaks at 35 days after the inhibitory neurons are generated, around postnatal day 28 (P28). When these cells were harvested from a donor mouse shortly after they were generated at embryonic day 13 (E13) and transplanted into the visual cortex of a P10 host, they migrated and differentiated into the same types of neurons in the same cortical layers that they would have become had they been left in the donor. Strikingly, they induced a second critical period of plasticity 35 days after transplantation, long after the end of the normal critical period of the host (Southwell et al., 2010). No other manipulation that we knew of, and certainly no other manipulation of inhibition, could do the same thing to give the brain of an older animal the plasticity it has in early life.

We have gone on in a series of papers with the members of our laboratories to study this phenomenon in the hope that understanding its mechanism would lead to a therapy for recovery from brain injury or maldevelopment, and a company (which I have no part in) was founded to explore the therapeutic use of neural transplantation. We found out that only two of the many types of interneurons had the capacity to rekindle juvenile plasticity after transplantation (Tang et al., 2014), and that the transplanted neurons had to be able to release their inhibitory neurotransmitter GABA in order to do so (Priya et al., 2019). We also found that the transplanted neurons trigger changes in host circuitry to create the second critical period rather than establishing a parallel circuit of their own (Hoseini et al., 2019). But we still do not know how they do it, and our work on this problem continues.

Alert Mice and Adult Plasticity

After completing a spectacular doctorate on zebrafish at Stanford, Cristopher Niell joined the laboratory to work on a mammal in which visual responses would have much greater specificity. Cris did the first really thorough and quantitative study of visual cortical receptive fields in the mouse (Niell and Stryker, 2008), a task that we had previously punted on, doing only enough to measure ocular dominance. Cris’s experiment was foundational. It was greatly facilitated by the use of 16-site silicon microelectrodes, which increased the rate at which we could measure responses by an order of magnitude over the tungsten electrodes (designed by David Hubel 45 years earlier) with their single recording site that we had previously used. Up to this point, we had always studied responses and plasticity in anesthetized animals, and my, and other, experiments had made it clear that plasticity is not induced under anesthesia. We wondered whether the properties of neurons were similar when the mice were alert, under conditions in which plasticity could be induced.

After trying several unfruitful approaches, we adopted the apparatus just designed in David Tank’s lab, in which a mouse with its head fixed stands or runs on a 20 cm polystyrene foam ball floating on air. Mice needed only a few minutes of experience to adapt to this apparatus, and they seemed alert and happy, ready to grab a sunflower seed or nibble at angel-hair pasta as readily as when they were in their home cage. We studied the receptive fields of neurons in the visual cortex in the alert animals exactly as we had done in anesthetized mice, and, to our relief, found that their properties were essentially identical (Niell and Stryker, 2010). However, the visual responses were much stronger when the mice were walking or running than when they were standing alert and still. We thought that this difference might be trivial, perhaps due to a little vibration of the eyes during locomotion, but when we made simultaneous recordings from the LGN, the responses did not change when the animals started to run. We concluded that we had discovered a new cortical state induced by locomotion that does not change spontaneous activity or the stimulus selectivity of each neuron but merely increases the gain of visual responses.

Cortical state had previously been studied only in sleep and during anesthesia, so we hoped to delineate the circuit that put the cortex into the high-gain state. Moses Lee, a medical doctor/doctoral student, joined Cris in stimulating the excitatory neurons of the midbrain locomotor center optogenetically, which made the mice run and put the cortex into the high-gain state. But the interesting finding was that turning the stimulus frequency or intensity down to the point that it no longer induced running still caused the change in cortical state. This implied that it was not making the legs move but some ascending projection that regulated cortical state (Lee et al., 2014). Tracking down which projection seemed difficult. A new postdoc from Josh Huang’s lab, Yu Fu, had studied and helped to create mouse lines that could be used to manipulate specific classes of inhibitory neurons. Yu Fu went directly to the visual cortex and labeled various types of neurons one at a time, looking for the cells that carried the signal of locomotion to the cortex. We knew that most visual cortical cells are not driven by anything at all in the dark, so we used 2-photon calcium imaging to look for cells that responded to locomotion in the dark. A minor class of interneurons expressing vasoactive intestinal peptide (VIP) fired reliably whenever the mice walked or ran, and none of the other cell types did so (Fu et al., 2014). These VIP cells received powerful cholinergic input from a specific nucleus of the basal forebrain, which receives input from the midbrain locomotor center. Optogenetically activating VIP cells in stationary mice mimicked the effect of locomotion on cortical state in sedentary mice, and photolytically damaging the VIP cells (blowing them away) prevented locomotion from putting the cortex into the high gain state.

Later experiments led by Yu Fu and Megumi Kaneko revealed a dramatic form of plasticity that takes place only when the cortex is in the high-gain state. When mice that were monocularly deprived for many months, mimicking human amblyopia ex anopsia, were shown a particular stimulus repeatedly during locomotion for an hour per day for five days as adults, the response of the visual cortex to that specific stimulus recovered as it would never have done otherwise (Kaneko et al., 2014). In intact adult mice, exposure to a specific stimulus during locomotion increased the response by 50%, and this increase persisted for weeks, while the same procedure had no effect when synaptic release from the VIP neurons was blocked (Fu et al., 2015). Megumi Kaneko tracked the responses of individual selective neurons using 2-photon microscopy and found that the persistent response enhancement, which we dubbed “stimulus-specific enhancement” (SSE), was not only stimulus-specific but also was specific to individual cortical neurons (Kaneko et al., 2017). Neurons selective for 45-degree lines were enhanced by exposure to 45-degree lines during locomotion, but exposure to 135-degree lines had no effect on them. Another postdoctoral fellow, Maria Dadarlat, took advantage of newer silicon probes with 64–128 recording sites that allowed simultaneous recordings from up to 100 single neurons. Her work showed that the representation of information about the visual world in the responses of cortical neurons was greatly increased during locomotion (Dadarlat and Stryker, 2017). To have the same degree of confidence in the identity of a stimulus being shown to a running mouse for 100 msec would take three to five times as long if the mouse were alert but just standing there.

We are actively pursuing the idea that this high-gain state, which in the mouse we can turn on by locomotion, is the one that in humans is turned on by selective attention. We are currently testing whether this is the circuit responsible for perceptual learning, which also requires selective attention.

Modeling Visual Cortical Circuits using a more Naturalistic Stimulus, Optic Flow.

Responses to the normal stimuli used in visual physiology experiments lend themselves to simple linear-nonlinear models but do not explain the reliable but highly selective responses of mouse visual cortical cells to what they see in the real world. Natural images, though, are hard to understand and mathematically nearly intractable. Optic flow is a ubiquitous feature of the natural visual world as an animal runs through it, but unlike natural images, it is well understood and mathematically tractable. My old friend Steven Zucker, a mathematician and computer scientist who had been an external faculty member of our Sloan Center for Theoretical Neuroscience in the 1990s, had done interesting work in his own lab on the properties of optic flow and its implications for perception. Steve and I decided to study optic flow in mice as a “baby step” toward understanding vision in the natural world and as a new stimulus to enrich a novel approach to modeling the neural circuits that give rise to visual cortical responses. Postdoctoral fellow Mahmood Hoseini, a doctor of physics who had rapidly become a spectacular experimental neuroscientist, used 128-site microelectrodes and found that many neurons in the mouse visual cortex respond strongly and selectively to optic flows that have no energy in the models of cortical responses derived from conventional grating stimuli (Dyballa et al., 2018). This collaboration is carried out by hour-and-a-half-long Zoom videoconferences every week between Steve and his student Luciano Dyballa at Yale and Mahmood and me at UCSF, and it works surprisingly well, perhaps because we all know one another from visits and are friends. We have reason to be optimistic that the new analytic approaches and data will give us insight into the operation of visual cortical circuits, and we are pursuing this work actively.

Antivivisectionists

At times, I have been the target of antivivisectionists who would like to put a halt to the animal research that is the only hope for ameliorating human injury and disease. Dealing with this has sometimes been challenging for me and my family, but I am sustained by the knowledge that the public is with us and that it is only a few extremists among the activists who might actually be dangerous.

In 1981, when I was a beginning assistant professor, antivivisectionists broke into the UCSF animal care facility, did some damage, and took videos of animals, including my cats, some of which had an eyelid sutured for studies of critical-period plasticity. Other cats in those cages were actually completely blind as a result of tetrodotoxin infused into their eyes, but of course they looked normal. Months later, the producers of 60 Minutes, then as now one of the most widely viewed programs on television, told the university that they were going to do a segment on the antivivisectionists using pictures of my cats, and they invited us to send someone to appear on the segment and respond. Wisely the university declined to send anyone. Fortunately, at that time the district attorney in San Francisco believed in law enforcement, and I was told that he threatened to charge CBS as an accessory-after-the-fact to the break-in if they used the videos. Eventually, it was agreed that CBS could use the videos so long as they did not identify the institution or investigator involved. The wonderful correspondent Ed Bradley hosted the 60 Minutes segment, in which unbelievably creepy people argued against animal research and narrated the videos from the break-in, trying to elicit sympathy for the poor cats with one eyelid sutured shut, comparing them to the “happy” ones jumping about the cage with both eyes open (which, unbeknownst to the antivivisectionists, were actually totally blind). Near the end of the segment, Ed Bradley asked the chief representative of the antivivisectionists whether, if his child had a disease that could be cured by the research being done on those cats, would he still want the research to be stopped. He replied with something like, “Well, I might be weak, but no, I would not want the research to be done.” Bradley’s last words before going to the commercial at the end of the segment were “You’ve got to be kidding!” That 60 Minutes segment, in which the true personalities and nature of the antivivisectionists were revealed to a wide public, was a disaster for their movement, and they left us alone for several more years. Surprisingly, CBS recycled its expensive videotapes in those days, and no copy of the segment still exists to provide the antivivisectionist’s exact quotation.

The most threatening episode for me came in 2001, when I was one of a number of keynote speakers at the International Union of Physiological Sciences meeting in Christchurch, New Zealand. Unknown to me, New Zealand, like the United Kingdom, had an active antivivisectionist movement, and I was surprised to be met at the airport by a secret service contingent that told me I should be under their guard for my entire time in the country. This was at a time when there was wide popular interest in animal research into critical periods because of its implications for child development, and I was scheduled to do several local television and radio shows, one of which was the New Zealand equivalent to PBS Science Friday. The first night, sleepless because of the time change, I snuck out of my hotel room to take a walk while the secret service slept in the two rooms to either side, and ended up being recognized and running from a group of antivivisectionists into a hotel that locked its door after me. The antivivisectionists were arrested by the police for trying to break down the door. Thereafter, I did what I was told by my guards.

Apparently, yellow journalism was then at least as prominent in New Zealand as in the United Kingdom. The day before I was to speak at the meeting, an open letter from the antivivisectionists was reproduced at the top of the front page of a major national newspaper:

The “good” California “doctor” is a target. Such evil should not be allowed to exist. Our efforts in the next few days will show the world that we will not tolerate the presence or existence of such a monster. While the “conference” has heavy protection, there are still many opportunities for us: Long-distance firearms, explosive devices, “accidents,” gas/chemical attack, additives to food and drink. These are just some of the resources we have access to, but there are some not listed. Before this person leaves New Zealand, he may be dead! Our only regret would be that his suffering would not be as long and hard as that of his innocent victims.

Another newspaper had a large picture of my face, above the fold on the front page, on a poster held up by one of the protesters.

I then declined to do any television, hoping not to be recognized as widely. However, I did do radio interviews about the science, but not about the politics. One interview had been scheduled for the mayor’s office but was moved, without informing the radio audience, to a more secure place. A group of antivivisectionists broke into the mayor’s anteroom and slammed the receptionist against the wall when she would not open the door to the office, which they then broke into. Fortunately, this assault was captured on video and the perpetrators were arrested.

At the same time, my family and I received a threatening letter at UCSF, which my secretary read to me over the phone. It seemed that this might not be an ordinary nut case but instead someone related to the New Zealand terrorists. I phoned the UCSF chancellor, and he and the UCSF police chief arranged with the Marin County sheriff to keep my house and family under 24-hour observation from a hillside nearby. Other than my wife and the school head and our next-door neighbor, no one else was informed, but our children were escorted by hand between the school and our car each day. As it turned out, the person making the threat was soon jailed for assaulting someone else, and the surveillance was ended.

What struck me most was the advice and encouragement I received from two courageous European scientists at the meeting who, unlike me, for whom the threats were transient and mostly far away, had endured continuing threats over years where they lived and worked, at the cost of great stress to them and their families. If they did not surrender and renounce animal research, then neither would I.

Outside Community Engagement

I have always believed in contributing to the wider community, and while I have served on the boards of various nonprofits and participated in MIT visiting committees and Howard Hughes Medical Institute investigator reviews, I have rarely had much free time. I have, however, devoted considerable time and energy to two institutions that are particularly close to my heart. I believe that Deep Springs college had a tremendous influence on me and that I owe it a lasting debt. I expect that I would have turned into an effete snob, a very different person, had I not gone there. So I was happy to join the board of trustees of the college and chair it for five years. I was proud that I could promptly and positively mobilize support to take care of major difficulties there, for some of which I shared the blame. UCSF is a health science campus without undergraduates, so it was exciting for me to be immersed in contemplating and helping to make the liberal arts education at Deep Springs more nearly ideal, as well as to review the operation of the ranch and of campus life. The limit of two four-year terms on the board left a hole in my existence when this thing that I had attended to and often worried about multiple times a week was no longer part of my life. Since then, I have been thrilled to see Deep Springs flourish under new leadership, becoming coeducational when at the time of the 100th anniversary of its founding, the California Supreme Court finally dismissed lawsuits that had prevented it from doing so.

Three years after the founding of the Allen Institute for Brain Science, I was asked to join its scientific advisory board (SAB). The Institute was creating a definitive and comprehensive atlas of gene expression in the mouse brain. Microsoft co-founder Paul Allen usually came to the SAB meetings and asked questions that stimulated further research. It was his vision to create a new kind of institution for brain research, where open, team science could flourish to do something that simply would never be done in academics or industry—to pursue large, well-defined scientific goals, with high-quality control and clear performance milestones. Inspired by the policy of the human genome project for prompt release of data to the wider community, the Institute adopted the motto “Fueling Discovery.” I bought into the vision completely and found my interactions with Paul, the other members of the SAB, the Institute president Allan Jones, and its leading scientists very exciting. Over the years since, my belief and involvement in the Allen Institute, which now includes Institutes for Cell Science and Immunology, has increased, and I am proud to have helped lead it on the course it has taken. With the untimely passing of Paul, my work on the board of directors, as well as on scientific advisory groups, has become a much larger responsibility, but one that I cherish. I do believe that some questions in biology will benefit enormously from the large-project, open, team science approach of the Allen Institute as a supplement to the conventional small-lab approach taken in academics.

Family

I had the great good fortune to fall in love with Barbara Poetter during the later portion of graduate school. She was then a freelance writer and later a book editor at Little, Brown, and we lived together, poor but happy, in Cambridge, Massachusetts. As the daughter of a management consultant who became a United Nations diplomat working on small-business development and who took his family to live in various developing countries, including Kenya, she had an understanding of the larger world that was rare among people I knew. She was amazingly self-sufficient, having traveled alone by bus through the Middle East at age 16, joining archeological digs and social service projects. Her self-sufficiency made it possible for me to do frequent all-night and weekend experiments and take our fun together when our work permitted. We married a few months before driving to San Francisco where I started at UCSF. She then worked as a copy editor on scientific books and papers, and we enjoyed the west-coast culture and natural world, eating dinner at 9:30 p.m. and splitting a bottle of inexpensive wine most nights until our children were born.

After two years, we had our first child, Matthew, and bought a house a five-minute drive from the lab. After another two years, we had a second, James, and then a third, Emily, three years later. Barbara worked 80% time after the first, 60% time after the second, and 40% time after the third, making it possible for me to work ridiculous hours in my lab. I went home for dinner, but lacking an office in our tiny house, it made sense for me to go back to the lab after the children went to sleep every night. My presence in the lab meant that I was there to participate in all of the late-night microelectrode recordings, and I believe it made our research much better. But it was possible for me to have both this and a wonderful family that did not suffer from my overwork only because Barbara was always there. The children were a delight, each one a completely different person, but all enjoyed our weekly excursions to Ocean Beach, 10 minutes away from our house, to the UCSF campus for swimming lessons, and to Golden Gate Park for bike riding and museum visits. I now regret that we did not take more trips to the mountains in the winter for cross-country skiing, which the children did from age 3 or 4, or more summer vacations in Europe, which happened only when I had accumulated enough frequent flyer miles to make the trips affordable, or in Hawaii, for which the airfare was cheaper. During our sabbatical year in Oxford when Matthew was 7, we lived on Boars Hill, and he and his brother went to the local school opposite the 14th-century church, whose vicar came weekly to the school to give moral instruction. It was a wonderful family time together, with lots of vacation in the United Kingdom and in France outside Oxford’s three eight-week terms per year.

Seven years later, I became department chair, and we moved across the Golden Gate Bridge to a bigger house in an idyllic community surrounded by redwoods where the public schools were great, the children could go everywhere on their bicycles, and I could no longer go to the lab after supper. We soon had our fourth child, Jenny Marie, and I had the gift of lots of time with her as the older children wanted to spend less and less time with parents. All of the children have found fulfilling careers, and all but Jenny Marie live in San Francisco. The three older ones have found wonderful spouses and have given us our first grandchild, with two more now on the way. All of us in the Bay area get together every few weeks for dim sum in the city, and we often see them at our house on weekends. They are the source of my greatest happiness.

Perspective

It is good for one’s self-esteem to realize that even scientists whose work changed the field mostly disappear. The stories of their lives and how their discoveries were made are forgotten, but the field continues in its altered direction. I was recently shocked to find that none of the 20 graduate students in our first-year course knew the name of Steve Kuffler—one of the figures in neuroscience I had admired most at their age. Yet they all knew about the center-surround receptive fields that Kuffler had discovered.

I was tremendously fortunate to be part of three institutions that each believed, with some justification, that it was creating the future. I feel lucky to have known the founders whose animating visions had created those institutions. Hans-Lukas Teuber founded a new Department of Psychology and Brain Science at MIT to study the mind as Helmholtz would have intended were he alive in the 1960s, from human patients through psychophysics, neuroanatomy, and neurophysiology to cognitive science. Steve Kuffler founded the Neurobiology Department at Harvard that came to define the term neurobiology, from biochemistry through neurophysiology. We at the UCSF Neuroscience Program and PIBS tried to be like Harvard’s department but more open, more humble, and freer to engage with our colleagues in the rest of modern biology than Harvard was when I was there. To be present in the early years in which these institutions were flourishing was truly thrilling.

I feel lucky to have had a life in science at the dawn of the true golden age of my field. Seemingly chance occurrences got me to this place: admission to Deep Springs, the high-paying job cleaning rat cages, the arbitrary choice to go to East Africa instead of graduate or medical school, the good fortune of rejection by Penn sending me to MIT to work with Peter Schiller, the chance that I gave a lunch seminar at Harvard neurobiology, and the flyers I took on ferrets and then on mice. The constant feature has been the good will and integrity of nearly everyone I have known in my career. My science friends, many of whom I did not have space to mention, have been a great joy. Most of all, it has an extraordinary privilege to work with the young people who have joined my lab, letting me profit from their energy, brilliance, and in many cases friendship, and I hope that I have given them some fraction of what my mentors gave me. Their names, in approximate chronological order, follow.

PhD Students:

Kathleen R. Zahs

Kenneth D. Miller

Holger Reiter

Barbara Chapman

Edward S. Ruthazer

Joshua Gordon

Takao Hensch

Deda C. Gillespie

Michael A. Silver

Sharif Taha

Jessica L. Hanover

Laila Dadvand

Matthew Caywood

Melinda Owens

Postdoctoral Fellows:

Axel Schoppmann

Margaret I. Law

Robert Levy

David Waitzman

Jonathan Horton

Gary Baker

Yoshio Hata

Michael Crair

Michela Fagiolini

Tony Pham

Joshua Trachtenberg

Christopher Trepel

Naomi Ruff

Naoum Issa

Virginia Desa

Marcos Frank

Valery Kalatsky

Jianhua Cang

Megumi Kaneko

Tatyana Sharpee

Masaaki Sato

Marianne Fyhn

Torkel Hafting Fyhn

Sunil Gandhi

Cristopher Niell

Dan Darcy

J. Sebastian Espinosa

Yu Fu

Maria Dadarlat

Nikhil Bhatla

Yujiao (Jennifer) Sun

Mahmood Hoseini

Benjamin Rakela

Research Faculty:

Antonella Antonini

Siegrid Löwel

Research Support:

Sheri Strickland Harris

References

Antonini, A. and Stryker, M.P. (1993) Development of individual geniculocortical arbors in cat striate cortex and effects of binocular impulse blockade. J. Neurosci. 13: 3549–3573.

Antonini, A. and Stryker, M.P. (1993) Rapid remodeling of axonal arbors in the visual cortex. Science 260: 1819–1821.

Antonini, A., Fagiolini, M., and Stryker, M.P. (1999) Anatomical correlates of functional plasticity in mouse visual cortex. J. Neurosci. 19: 4388–4406.

Blakemore C. and Mitchell D.E. (1973) Environmental modification of the visual cortex and the neural basis of learning and memory. Nature 241: 467–468.

Cang, J.C., Renteria, R.C., Kaneko, M.., Liu, X., Copenhagen, D.R., and Stryker, M.P. (2005) Development of precise maps in visual cortex requires patterned spontaneous activity in the retina. Neuron 48: 577–589.

Cang, J.C., Wang, L., Stryker, M.P., and Feldheim, D.A. (2008) Roles of ephrin-As and structured activity in the development of functional maps in the superior colliculus. J. Neurosci. 28: 11015–11023.

Cang, J.C., Kaneko, M., Yamada, J., Woods, G., Stryker, M.P., and Feldheim, D.A. (2005) Ephrin-As Guide the Formation of Functional Maps in the Visual Cortex. Neuron 48: 577–589.

Cang, J.C., Niell, C.M., Liu, X., Pfeiffenberger, C., Feldheim, D.A., and Stryker, M.P., (2008) Selective Disruption of One Cartesian Axis of Cortical Maps and Receptive Fields by Deficiency in Ephrin-As and Structured Activity. Neuron 57: 511–523.

Chapman, B. and Stryker, M.P. (1993) Development of orientation selectivity in ferret visual cortex and effects of deprivation. J. Neurosci. 13: 5251–5262.

Chapman, B., Stryker, M.P., and Bonhoeffer, T. (1996) Development of Orientation Preference Maps in Ferret Primary Visual Cortex. J. Neurosci. 16: 6443–6453.

Chapman, B., Zahs, K.R., and Stryker, M.P. (1991) Relation of cortical cell orientation selectivity to alignment of receptive fields of the geniculocortical afferents that arborize within a single orientation column in ferret visual cortex. J. Neurosci. 11: 1347–1358.

Crair, M.C., Gillespie, D.C., and Stryker, M.P. (1998) The role of visual experience in the development of columns in cat visual cortex. Science 279: 566–570.

Crair, M.C., Horton, J.H., Antonini, A., and Stryker, M.P. (2001) Emergence of ocular dominance columns in cat visual cortex by 2 weeks of age. J. Comp Neurol. 430: 235–249.

Dadarlat, M.C. and Stryker, M.P. (2017) Locomotion enhances neural encoding of visual stimuli in mouse V1. J. Neurosci. 37: 3764–3775.

Dyballa, L., Hoseini, M.S., Dadarlat, M.C., Zucker, S.W., and Stryker, M.P. (2018) Flow stimuli reveal ecologically-appropriate responses in mouse visual cortex. Proc. Nat. Acad. Sci. USA. 115:11304–11309.

Fu, Y., Kaneko, M., Tang, Y., Alvarez-Buylla, A., and Stryker, M.P. (2015) A cortical disinhibitory circuit for enhancing adult plasticity. eLife 2015; 10.7554/eLife.05558.

Fu, Y., Tucciarone, J., Espinosa, J.S., Sheng, N., Darcy, D., Nicoll, R.A., Huang, Z.J., and Stryker, M.P. (2014) A cortical circuit for gain control by behavioral state. Cell 156: 1139–1152.

Galli L. and Maffei L. (1988) Spontaneous impulse activity of rat retinal ganglion cells in prenatal life. Science 242: 90–91.

Gillespie, D.C., Crair, M.C., and Stryker, M.P. (2000) Neurotrophin-4/5 alters responses and blocks the effect of monocular deprivation in cat visual cortex during the critical period. J. Neurosci. 20: 9174–9186.

Gordon, J.A. and Stryker, M.P. (1996) Experience-dependent plasticity of binocular responses in the primary visual cortex of the mouse. J. Neurosci. 16: 3274–3286.

Gordon, J.A., Cioffi, D., Silva, A.J., and Stryker, M.P. (1996) Deficient plasticity in the primary visual cortex of a-calcium/calmodulin-dependent protein kinase II mutant mice. Neuron 17: 731–741.

Hanover, J., Huang, ZJ., Tonegawa, S., and Stryker, M.P. (1999) BDNF overexpression induces precocious critical period in mouse visual cortex. J. Neurosci. 19:RC40,1–5.

Hata, Y. and Stryker, M.P. (1994) Control of thalamocortical afferent rearrangement by postsynaptic activity in developing visual cortex. Science 265: 1732–1735.

Hensch, T.K. and Stryker, M.P. (1996) Ocular dominance plasticity under metabotropic glutamate receptor blockade. Science 272: 554–557.

Hensch, T.K. and Stryker, M.P. (2004) Columnar architecture sculpted by GABA circuits in developing cat visual cortex. Science 303: 1678–1681.

Hensch, T.K., Fagiolini, M., Mataga, N., Stryker, M.P., Baekkeskov, S., and Kash, S.F. (1998) Local GABA circuit control of experience-dependent plasticity in developing visual cortex. Science 282: 1504–1508.

Hoseini, M.S., Rakela, B., Flores-Ramirez, Q., Hasenstaub, A.R., Alvarez-Buylla, A., and Stryker, M.P. (2019) Transplanted cells are essential for the induction but not the expression of cortical plasticity. J.Neurosci. 39: 1430–1419.

Hubel, D.H. and Wiesel, T.N. (1963) Receptive fields of cells in striate cortex of very young, visually inexperienced kittens. J. Neurophysiol. 26: 994–1002.

Hubel, D.H., Wiesel, T.N., and Stryker, M.P. (1977) Orientation columns in macaque monkey demonstrated by the 2-deoxyglucose autoradiographic method. Nature 269: 328–330.

Hubel, D.H., Wiesel, T.N., and Stryker, M.P. (1978) Anatomical demonstration of orientation columns in macaque monkey. J. Comp. Neurol. 177: 361–380.

Huberman, A.D., Stellwagen D., and Chapman, B. (2002) Decoupling eye-specific segregation from lamination in the lateral geniculate nucleus. J. Neurosci. 22: 9419–9429

Kalatsky, V. A. and Stryker, M.P. (2003) New paradigm for optical imaging. Temporally encoded maps of intrinsic signal. Neuron 38: 529–545.

Kaneko, M. and Stryker, M.P (2014) Sensory experience during locomotion promotes recovery of function in adult visual cortex. eLife 2014;3:e02798.

Kaneko, M., Fu Y., and Stryker, M.P. (2017) Locomotion induces stimulus-specific response enhancement in adult visual cortex. J. Neurosci. 37: 3532–3543.

Kaneko, M., Hanover, J.L., England, P.M., and Stryker, M.P. (2008a) TrkB kinase required for recovery but not loss of cortical responses following monocular deprivation. Nature Neuroscience 11: 497–504.

Kaneko, M., Stellwagen, D., Malenka, R.C., and Stryker, M.P. (2008b) TNFα mediates one component of competitive, experience-dependent plasticity in developing visual cortex. Neuron 58: 673–680.

Lee, A.M, Hoy, J.L., Bonci, A., Wilbrecht, L., Stryker, M.P., and Niell, C.M. (2014) Identification of a brainstem circuit regulating visual cortical state in parallel with locomotion. Neuron 83: 455–466.

LeVay, S., Stryker, M.P., and Shatz, C.J. (1978) Ocular dominance columns and their development in layer IV of the cat’s visual cortex: a quantitative study. J. Comp. Neurol. 179: 2230–2244.

McLaughlin, T., Torborg, C.L., Feller, M.B., and O’Leary, D.D. (2003) Retinotopic map refinement requires spontaneous retinal waves during a brief critical period of development. Neuron. 40: 1147–1160.

Meister, M., Wong, R.O., Baylor, D.A., and Shatz, C.J. (1991) Synchronous bursts of action potentials in ganglion cells of the developing mammalian retina. Science 252: 939–943.

Merzenich, M.M., Nelson, R.J., Stryker, M.P., Cynader, M., Schoppmann, A., and Zook, J.M. (1984) Somatosensory cortical map changes following digit amputation in adult monkeys. J. Comp. Neurol. 224: 591–605.

Miller, K.D., Chapman, B., and Stryker, M.P. (1989) Visual responses in adult cat visual cortex depend on N-methyl-D-asparate receptors. Proc. Nat. Acad. Sci. USA 856: 5183–5187.

Miller, K.D., Keller, J.B., and Stryker, M.P. (1989) Ocular dominance column development: analysis and simulation. Science, 245: 605–615.

Newell, L.J. (2015) The electric edge of academe: The saga of Lucien L. Nunn and Deep Springs College. Salt Lake City: University of Utah Press.

Niell, C.M. and Stryker, M.P. (2008) Highly selective receptive fields in mouse visual cortex. J. Neurosci 28: 7520–7536.

Niell, C.M. and Stryker, M.P. (2010) Modulation of visual responses by behavioral state in mouse visual cortex. Neuron 65: 472–479.

Norcia A.M. and Tyler C.W. (1985) Spatial frequency sweep VEP: visual acuity during the first year of life. Vision Res. 251399-1408.

Owens, M.T., Feldheim, D.A., Stryker, M.P., and Triplett, J.W. (2015) Stochastic interaction between neural activity and molecular cues in the formation of topographic maps. Neuron 87: 1261–1273.

Pettigrew J.D. (1974) The effect of visual experience on the development of stimulus specificity by kitten cortical neurones. J. Physiol. 237: 49–74.

Priya, R., Rakela, B., Kaneko, M., Spatazza, J., Larimer, P., Hoseini, M.S., Hasenstaub, A.R., Alvarez-Buylla, A., and Stryker, M.P. (2019) Vesicular GABA transporter is necessary for transplant-induced critical period plasticity in mouse visual cortex. J. Neurosci. 39: 2635–2648.

Quarton, G., Schmitt, F., and Melnechuk, E. (Eds.) (1967) Neuroscience: a study program. New York: Rockefeller University Press.

Ruthazer, E.S. and Stryker, M.P. (1996) The role of activity in the development of long-range horizontal connections in area 17 of the ferret. J. Neurosci. 16: 7253–7269.

Schiller, P.H. and Stryker, M.P. (1972) Single-unit recording and stimulation in superior colliculus of the alert monkey. J. Neurophysiol. 35: 915–924.

Schiller, P.H., Stryker, M.P., Cynader, M., and Berman, N. (1974) Response characteristics of single cells in the monkey superior colliculus following ablation or cooling of visual cortex. J. Neurophysiol. 37: 181–194.

Schoppmann, A. and Stryker, M.P. (1981) Physiological evidence that the 2-deoxyglucose method reveals orientation columns in cat visual cortex. Nature 293: 574–576.

Shatz, C.J. and Stryker, M.P. (1978) Ocular dominance in layer IV of the cat’s visual cortex and the effects of monocular deprivation. J. Physiol. 281: 267–283.

Shatz, C.J. and Stryker, M.P. (1988) Prenatal tetrodotoxin infusion blocks segregation of retinogeniculate afferents. Science 242: 87–89.

Sherk, H. and Stryker, M.P. (1976) Quantitative study of cortical orientation selectivity in the visually-inexperienced kitten. J. Neurophysiol. 39: 63–70.

Southwell, D.G., Froemke, R.C., Alvarez-Buylla, A., Stryker, M.P., and Gandhi, S.P. (2010) Cortical plasticity induced by inhibitory neuron transplantation. Science 237: 1145–1148.

Stellwagen, D. and Malenka, R.C. (2006) Synaptic scaling mediated by glial TNF-alpha. Nature 440: 1054–1059.

Stryker, M.P. (1986) The role of neural activity in rearranging connections in the central visual system, in The biology of change in otolaryngology, R.W. Ruben et al., eds., pp. 211–224. Amsterdam: Elsevier.

Stryker, M.P. (1989) Evidence for a possible role of spontaneous electrical activity in the development of the mammalian visual cortex, in Problems and concepts in developmental neurophysiology, P. Kellaway and J.L. Noebels, eds., pp. 110–130. Baltimore: Johns Hopkins University Press.

Stryker, M.P. (1991) Temporal associations [News and Views]. Nature 354: 108–109.

Stryker, M.P. (1992) Elements of visual perception [News and Views]. Nature 360: 301–302.

Stryker, M.P. and Harris, W.A. (1986) Binocular impulse blockade prevents formation of ocular dominance columns in the cat’s visual cortex. J. Neurosci. 6: 2117–2133.

Stryker, M.P. and Sherk, H. (1975) Modification of cortical orientation-selectivity in the cat by restricted visual experience: a reexamination. Science 190: 904–906.

Stryker, M.P. and Zahs, K.R. (1983) ON and OFF sublaminae in the lateral geniculate nucleus of the ferret. J. Neurosci. 3: 1943–1951.

Stryker, M.P., Jenkins, W.M., and Merzenich, M.M. (1987) Anesthetic state does not affect the map of the hand representation within area 3B somatosensory cortex in owl monkey. J. Comp. Neurol. 258: 297–303.

Stryker, M.P., Sherk, H., Leventhal, A.G., and Hirsch, H.V.B. (1978) Physiological consequences for the cat’s visual cortex of effectively restricting early experience with orientation. J. Neurophysiol. 41: 896–909.

Sun Y.J., Espinosa, J.S., Hoseini, M.S., and Stryker M.P. (2019) Experience-dependent structural plasticity at pre- and postsynaptic sites of layer 2/3 cells in developing visual cortex. (*co-first authors) Proc. Nat. Acad. Sci. USA116: 21812–21820.

Tang, Y., Stryker, M.P., Alvarez-Buylla, A., and Espinosa, J.S. (2014) Cortical plasticity induced by transplantation of embryonic somatostatin or parvalbumin interneurons. Proc. Nat. Acad. Sci. USA 111: 18339–18344.

Trachtenberg, J.T. and Stryker, M.P. (2001) Rapid anatomical plasticity of horizontal connections in developing visual cortex. J. Neurosci. 21: 3476–3482.

Trachtenberg, J.T., Trepel, C., and Stryker, M.P. (2000) Rapid extragranular plasticity in the absence of thalamocortical plasticity in the developing primary visual cortex. Science 287: 2029–2032.

Triplett, J.W., Owens, M.T., Yamada, J., Lemke, G., Cang, J., Stryker, M.P., and Feldheim, D.A. (2009) Retinal input instructs alignment of visual topographic maps. Cell 139: 175–185.

Wurtz, RH and Goldberg, M.E. (1971) Superior colliculus cell responses related to eye movements in awake monkeys. Science 171: 82–84.

Zahs, K.R. and Stryker, M.P. (1985) The projection of the visual field onto the lateral geniculate nucleus of the ferret. J. Comp. Neurol. 241: 210–224.

Larry W. Swanson

BORN:

Camp Lejeune, North Carolina

December 13, 1945

EDUCATION:

Pomona College, BS in Biochemistry (1968)

Washington University School of Medicine, PhD in Neurobiology (1972)

APPOINTMENTS:

Postdoctoral Fellow (Lab of W. Maxwell Cowan), Washington University (1972–1974)

Postdoctoral Fellow (Lab of Rita Levi-Montalcini), Washington University (1974–1976)

Research Assistant Professor, Department of Anatomy and Neurobiology, Washington University (1976–1979)

Assistant Professor, Department of Anatomy and Neurobiology, Washington University (1979–1980)

Staff Scientist to Senior Member, Salk Institute for Biological Studies (1980–1990)

Assistant Adjunct Professor to Adjunct Professor, UC San Diego (1980–1990)

Investigator, Howard Hughes Medical Institute, at the Salk Institute (1985–1990)

Professor, Departments of Biological Sciences and Psychology, USC (1990–present)

Appleman Professor of Biological Sciences, USC (1995–present)

Founding Coordinator, Neuroscience Graduate Program (university-wide), USC (1996–2004)

Dean of Research, The College (M.O. Schapiro, Dean), USC (1998–2000)

Director, NIBS-Neuroscience Program (university-wide), USC (2001–2004)

NIMH Board of Scientific Counselors (2006–2011)

Visiting Scholar, Department of Neurobiology, UCLA (2007–2013)

University Professor, University of Southern California (2012–present)

Visiting Scientist, Department of Neuroscience, Columbia University (2012, 2018)

Visiting Scholar, Sainsbury Wellcome Centre for Neural Circuits and Behavior, UCL (2019)

HONORS AND AWARDS (SELECTED)

Javits Distinguished Neuroscience Investigator Awards, NINDS (1986–1993, 2006–2013)

100 most cited scientific researchers of the 1980s (one of two neuroscientists), ISI (1991)

100 most cited neuroscience researchers, 1980-2000; Institute for Scientific Info. (2001)

President, The Cajal Club (2004–2006)

Fellow, American Academy of Arts and Sciences (2005)

Member, National Academy of Sciences (2010)

Member, Grolier Club (2010)

President, Society for Neuroscience (2012–2013)

Secretary General, International Brain Research Organization (2015–2017)

Throughout his career, Larry W. Swanson has investigated the basic structure-function organization of mammalian neural systems controlling the three classes of motivated behavior that assure survival in all animals: ingestive (eating and drinking), reproductive (sexual and parental), and agonistic (fight-or-flight). Because the mechanistic explanation of behavior ultimately involves all parts of the nervous system, he has also applied network analysis tools to understand the basic wiring diagram of the nervous system.

Larry W. Swanson

“To extend our understanding of neural function to the most complex human physiological and psychological activities, it is essential that we first generate a clear and accurate view of the structure of the relevant centers, and of the human brain itself, so that the basic plan—the overview—can be grasped in the blink of an eye.”

—Santiago Ramón y Cajal, 1909–1911 (chap. 2, p. 45)

Early Years

I was born at the end of the deadliest conflict in history and the beginning of an American golden age of economic prosperity. During most of World War II my father, Bernard, had served in the Pacific Theater as a major in the Marine Corps, and then toward the end became deputy chief for logistics at Camp Lejeune, North Carolina, a huge Marine Corps Base. He was born and raised on a farm in the American heartland near Hastings, Nebraska, and graduated from Hastings College before the United States entered the hostilities.

In contrast, my mother, Shirley, was born and raised in Las Vegas, Nevada, which at the time, still had many trappings of the Wild West. She graduated from the University of California, Los Angeles (UCLA) before joining the war effort as an administrative assistant to the Truman Commission investigating defense industry fraud and corruption in Washington, DC. It was there, on a blind date, that she met my father, and they were married in 1942 in San Diego, just before he shipped out to the Pacific islands. I made my entrance, almost exactly four months after V-J Day, on December 13, 1945, in the U.S. Naval Hospital at Camp Lejeune. My mother’s roommate was Annie Glenn (Oncken, 1962), who was also having her first child—with her husband John, a highly decorated Marine Corps fighter pilot who, just 17 years later in 1962, would be the first American to orbit the Earth.

When I was about a month old, my parents moved to Las Vegas, and my father started and ran, with the help of my mother’s father, a company that bottled and distributed soft drinks. This grandfather, William E. “Pop” Ferron, grew up in Utah. His own grandfather, General Friedrich Salomon, was surveyor general of Utah and had mapped out the territory with Brigham Young. Pop’s father, Augustus Ferron, was a Central Pacific railroad engineer with a degree from City College of New York. He had been at Promontory Summit, Utah territory, when the first transcontinental railroad was completed there in 1869, and he loved to have his two boys tag along on field trips through the state. When the time came, Pop headed east for a degree at the Philadelphia College of Pharmacy. After graduating, the adventuresome young man traveled south to Columbia for a gold mining venture with his brother, meant to raise a stake for starting his own business.

For his first business, Pop chose Las Vegas, which, roughly translated, means “the Meadows,” because it had natural springs in the middle of the Mojave Desert. This made Las Vegas a convenient railroad stopping point for water and ice between Salt Lake City and Los Angeles, and, as he correctly surmised, an area of future growth. In 1917, he moved there with his bride, Ruth Cooper, whose family had roots in Stowe, Vermont.

Ruth was horrified. With a population of less than 2,000, Las Vegas still had dirt streets and wooden sidewalks, having incorporated only six years earlier. Undaunted, Pop used his gold mining stake to open the first independent pharmacy in Las Vegas, and respectability followed quickly. He was elected its third mayor in 1920 (UNLV Special Collections and Archives, 2019).

As a child, my maternal grandparents were relatively well off and highly respected in the community. At the same time, they had an adventurous spirit and loved to travel the world. They had the means to allow Ruth and their girls to travel to Southern California in the summers to escape the heat. They would travel by car (a two-day trek back then) followed by another car in case the first broke down. Being stranded in the desert was something to be feared especially as there were so few towns between Las Vegas and Los Angeles. This summer sojourn would continue into my youth, contributing greatly to my love of California.

In contrast, my paternal grandparents, Harry and May (née Joyce) Swanson, were from pioneer Swedish and Irish farming families that had emigrated to Nebraska in the 1870s. They were salt of the earth Midwesterners who moved to Las Vegas after the war to be close to their son and his family. The Ferron grandparents lived in a big house that we visited semiformally on special occasions; the Swanson grandparents lived in a working-class neighborhood and were a frequent, loving, and joyous presence in our lives.

I attended Catholic schools from first grade through high school. As a young child, I assembled a stamp collection, then a mineral collection, and eventually lost interest in them both; I’ll get to my adult bibliomania later. Overall, it was a happy suburban upbringing, with a flavor of the Western U.S. adventuresome spirit, best displayed by the annual Helldorado Days festival celebrating the cowboy origins of Las Vegas. We’d all dress up in our boots and hats and watch the parade from the window of Pop’s drugstore. And as often as possible, my friends, brothers Dave and Tim, and I explored the undeveloped desert a couple of blocks from our house looking for scorpions, snakes, weird cacti, and anything else unusual that caught our attention.

We were mostly isolated from the gambling-resort industry that grew exponentially in Las Vegas after the war. It was a different world. But it was fun every now and then to drive with the family down Fremont Street and along The Strip (where all of the hotel casinos were concentrated) and see the latest neon sign monstrosities. Our family rarely went to shows, although Gram and Pop would take us to one or another of the extravaganzas on our birthdays, always forgetting that they would include parades of semi-nude chorus girls strutting to the hit parade of the day. For the most part, I was unaware of how segregated our community was until something would escape the lips of Gram. I remember seeing Harry Belafonte with his young daughter on his shoulders at the Helldorado parade, a lovely family moment that was marred by my grandmother exclaiming, “What’s he doing here?”

Growing up, I experienced two serious family events with long-term consequences. First, my youngest brother Tim had encephalitis when he was four years old (and I was nine). A private emergency flight from Las Vegas to the UCLA Medical Center saved his life, although recovery was slow, and subtle effects on motor and cognitive functions remain to this day. And second, after this tragedy, my father’s long-term drinking problem grew much worse. He became more isolated from the family, and, finally, he died of alcoholism when he was only 48 years old. I cannot honestly say that he had any positive influence on my life or my future.

I did not show any real academic potential until high school, when I emerged as one of the better students in science and math classes. Keep in mind the bar was very low—the nun who taught us math in eighth grade couldn’t do fractions. I also enjoyed English literature and art appreciation (those nuns had a better handle on these subjects). There was also plenty of time for friends and sports. I liked playing tennis, baseball, and basketball. In my junior year, our team won the Nevada State Division A Basketball Championship, defeating the Winnemucca Buckaroos, though I rode the bench for most of that game.

When the time came to think about college, there was no counseling program at Bishop Gorman High School, so I just applied to the University of California, Santa Barbara (UCSB) because I loved the ocean (those summer trips with my family, beginning when I was two, had a direct influence on this choice), and to Pomona College in Claremont, California, because the daughter of one of my mother’s friends went there.

Pomona College and the Glimmerings of Neuroscience

I was accepted to UCSB and wait-listed at Pomona College—but eventually was offered a place at the small private institution on the fringes of the Los Angeles metropolitan region at the base of Mt. San Antonio, the tallest peak in the San Gabriel Mountains. I went there thinking I wanted to be a physics major but struggled mightily with the introductory courses. My background at the tiny Catholic high school in Las Vegas had been woefully inadequate.

But two things happened in my freshman year: I did very well in my introductory psychology and human evolution courses, and most important, Francis Crick visited Pomona College for a week in the spring of 1965, to present the Robbins Lecture Series (Wellcome Library, 2020). He and James Watson had won the Nobel Prize three years earlier for their double-helix model of DNA and its implications for information transfer in living organisms.

Crick was now working on the “triplet code” involved in synthesizing protein from mRNA. In his first lecture, he wrote down on the blackboard a list of the known triplets, and in each of the next three lectures, he added ones that had been discovered since the previous lecture. It was a memorable experience, which was only heightened by his attendance at a “keg (beer-drinking) party” in the woodsy part of campus where a good time could be had by all—led by the charming, witty, and approachable Nobelist. Many years later when the University of Southern California (USC) faculty wanted to invite Crick for a lecture, his only stipulation was that the invitation had to come from the students.

Crick’s visit stimulated me to switch from physics to chemistry in my sophomore year. Two events the summer before also had an important influence on my future direction. Academically, I took a superb course in abnormal psychology at UCLA and became even more intrigued with psychology as a discipline. And socially, the Watts Riots took place in the middle of August 1965, just before I was to return to Claremont. The two Los Angeles communities are only about 40 miles apart geographically, but they are vastly separated culturally. This event was part of the much broader concerns of the 1960s: the civil rights and feminist movements along with anti–Vietnam War protests—to which I and the majority of my classmates at Pomona (and at colleges and universities around the country) were deeply committed.

The summer between my sophomore and junior years, I worked in Doug Henning’s organic chemistry lab at Pomona, separating the terpenes in pine tar. I was miserable both with it and at it. So, I switched again—to a new specialty at Pomona, biochemistry. I also began taking more courses in comparative vertebrate anatomy and physiology, as well as in physiological psychology. I was introduced to the latter by Clifton Trafton, whose course on motivation and emotion, with a wonderful textbook by Paul Thomas Young, continues to inspire me. Two other illuminating textbooks were Richard Thompson’s Foundations of Physiological Psychology, and Alfred Romer’s The Vertebrate Body. For my term paper in comparative anatomy, I chose the organization of pathways between brain and spinal cord because they seemed like an obvious link between cognition, motivation, and behavior. I was pretty much overwhelmed, but intrigued, by the complexity I began reading about. But, unlike my response to organic chemistry, I could easily see myself doing productive and interesting research on topics like these.

This formative undergraduate experience with molecular biology, psychology, and zoology at Pomona was directly aligned with physiological psychology, an already established branch of psychology. With the guidance of Clint Trafton, I began (in 1967) investigating graduate programs in the newly emerging interdisciplinary field of neurobiology. I found only two—at the University of Washington and at Washington University in St. Louis. I was rejected at the former and wait-listed at the latter, but eventually I was accepted just before graduation in 1968.

The previous 12 months had been socially invigorating. On one hand, the 1967 Summer of Love in San Francisco had spread quickly to college campuses in Los Angeles. But on the other, Vietnam War protests and Martin Luther King’s assassination in Memphis on April 4 led many of us at graduation to wear black armbands over our academic robes. My mother was quite dismayed by this action. Shortly thereafter, on June 5, my friends and I witnessed the assassination of Robert Kennedy on live television. I was reminded of sitting at my desk as a high school senior and hearing the principal, a priest, announce over the intercom system that President John Kennedy had been shot and killed in Dallas.

Localizing Eating and Drinking Hot Spots at Washington University

In August 1968, I drove my Volkswagen beetle with its Gene McCarthy bumper sticker to St. Louis and a whole new world. This is where I got my doctorate, postdoctoral experience, and first academic job. More important, it’s also where I met my wife Neely and we had our son, Reid.

Moving from Southern California to St. Louis in this era was culture shock, but I quickly recovered. I met Neely playing volleyball in October. We went to a Marx Brothers movie and a James Brown concert, and we have been best friends ever since. She was a French major from Chicago, and we got married at Bond Chapel (University of Chicago) on August 15, 1970. Her family could not have been more different than mine. Her father, Webb, grew up poor in rural Tennessee, went to graduate school at the University of Chicago after serving in the Army during the war, and became a labor relations executive for Sears, Roebuck and Company. In contrast, her mother Gaby’s family were Romanian Jews who emigrated to Paris. She spent the war years in hiding with her mother while her father was imprisoned in a labor camp outside Paris. The young (she was 16 at the time) urban Holocaust refugee met her American soldier from the hills of Tennessee in Cannes on the French Riviera and were married a year later. Webb would be a great and loving influence on me for the short time I knew him. He died of a Circle of Willis aneurysm at the age of 52, shortly after Neely and I married.

Before arriving in St. Louis, I had indicated a preference to work with Robert Wurtz, who was doing fascinating research on learning mechanisms in primates, but he had just moved to the National Institutes of Health (NIH). I was assigned instead to a young assistant professor, Vernon Perez, in the Psychiatry Department’s Laboratory of Neuropsychology, who was proposing to test the hypothesis that “brain-specific” proteins influence the expression of motivated behaviors. The first two, S-110 and 14-3-2, had just been discovered in 1965 in that department by Blake Moore, and this was an exciting project to get started on.

Three young researchers formed the core of the Laboratory of Neuropsychology, Perez, Ted Cicero, and Larry Sharpe. They had all trained at Purdue with Robert D. Myers, who pioneered methods for injecting substances, and sampling fluids, in the brains of conscious, behaving rats, rabbits, and nonhuman primates using permanently implanted cannulae. I spent almost a year making hundreds of microinjections of S-100 and 14-3-2 into many different parts of the rat brain and recording food and water intake, as measures of hunger and thirst—with no statistically significant effects. In hindsight, this was not surprising; S-100 is expressed by astrocytes and 14-3-2 is a neuron-specific enolase involved in glycolysis. Despite the obvious failure of this approach, Perez wanted me to continue to push ahead in hopes of finding something, anything, to report for his grant.

The rationale for manipulating ingestive behaviors was sound. It was based on the groundbreaking work of Sebastian (Pete) Grossman, who, for his doctoral thesis work at the University of Chicago (Grossman, 1960), invented a method for delivering minute amounts of neurotransmitter-related molecules into discrete parts of the brain of freely moving rats and measuring the behavioral effects. He discovered that cholinergic drugs induced drinking behavior and adrenergic drugs induced eating behavior when delivered to the same site in the hypothalamus. Most important, he hypothesized that there may be neurotransmitter-coded systems in the brain for different classes of motivated behavior. This effect fascinated me, and the hypothesis has been the inspiration for my research program ever since.

I first saw this effect in Larry Sharpe’s lab. When the experiments with Perez began looking unproductive, I asked Sharpe if I could work on ingestive behaviors with him and he agreed. After reading the literature, I thought the burning question in the field centered on localization of function (that is, exactly what parts of the brain are activated by microinjected neurotransmitter-related molecules?) and the clearest obstacle to progress was the relatively large volumes used to deliver the molecules in rat. Typically, the volume was around 1 µl (1 mm³) with a diffusion gradient that could reach at least 2 mm in diameter—which invariably spread to include multiple brain areas in the hypothalamus and other parts of the limbic system, hopelessly confounding interpretation. So, my first project was to develop a method for delivering much smaller volumes to the brain of freely moving animals. The results were a method for accurately and reliably delivering volumes as small as 0.04 µl (40 nl), my first research paper as lead author (Swanson et al., 1972), and as will become apparent later, a big advantage when I began my postdoctoral work in neuroanatomy.

Based on more than 1,000 forebrain and midbrain microinjections in the rat, the most sensitive and reliable hot spot for drinking induced by carbachol (a cholinergic agonist) and angiotensin II was localized to the periventricular hypothalamic zone, centered in the paraventricular nucleus (Swanson and Sharpe, 1973)—and this finding was confirmed in the monkey (Sharpe and Swanson, 1974). We were also fortunate to characterize the central angiotensin II receptors involved in the drinking response with Phil Needleman, who had synthesized a number of analogs, and also suggested pharmacological tests for cholinergic and adrenergic involvement (Swanson et al., 1973). By 1976, Needleman became chair of the pharmacology department before leaving for industry, eventually assuming the presidency of Searle in 1993.

The intellectual environment in the newly created Neurobiology Graduate Program was the best I have experienced in my career. Most of the chairs of the relevant departments showed up to seminars, leading by example, and it was a distinguished group: Max Cowan (anatomy), Carleton Hunt (physiology), Bill Landau (neurology), Oliver Lowry (pharmacology), and Roy Vagelos (biological chemistry). And there was the popular Saturday morning seminar series for students and faculty, with groups of presentations focused on particular topics and organized by Cowan.

My home department (psychiatry) was also special. It was led by Eli Robins and was one of the first departments of its kind in the United States to abandon psychoanalysis for clinically and experimentally based approaches to mental illness—hence, its Laboratory of Neuropsychology. And I learned more about critical thinking and basic experimental design from Larry Sharpe than anyone. He had a contrarian spirit that did not fit well in a clinical department, especially because he held a doctorate but was not a medical doctor, but he was my best friend in St. Louis at the time. On weekends, we often continued our lab discussions on the tennis court.

Neural Circuit Organization and the Neuroanatomy Revolution

As my thesis work wound down, I began thinking about postdoctoral positions and decided to pursue the behavioral hot spot I had identified. Following Grossman’s original hypothesis, I wondered what neural connections might form the “thirst circuit” with its periventricular hypothalamic “drinking center.” This seemed like one of the more tractable problems in behavioral neurobiology because so much was known about the relatively straightforward physiology of body water regulation, making functional interpretations of circuit data more readily apparent. So, in 1971, off I went to the first annual meeting of the Society for Neuroscience at the Shoreham Hotel in Washington, DC, searching for a postdoc. I knew virtually none of the 1,200 attendees but did manage to interview four or five potential mentors working on one aspect of circuit mapping or another.

Because Oxford-trained Max Cowan was one of the leading neuroanatomists in the world, and because he was on my thesis advisory committee and had invited me to attend his lab meetings, I went to him for advice about which postdoctoral position to choose. In characteristic fashion, he critiqued each person I had in mind, and suggested instead that I stay and work with him. He said they had just developed an ideal method for the type of circuit analysis I wanted to learn and handed me a preprint of the soon-to-be-famous paper describing the autoradiographic method (ARGM) for tracing connections in the brain (Cowan et al., 1972). It had three fundamental advantages over the degeneration-based methods then in use: it was far more sensitive and thus had far fewer false negative results; it did not involve axons-of-passage that lead to false positive results; and it relied on the cell biology (anterograde intra-axonal transport of radiolabeled proteins) of intact neurons rather than on lesion-induced pathological changes. Cowan’s offer was immediately accepted.

Earlier degeneration studies suggested that limbic parts of the cerebral hemispheres provide important inputs to the hypothalamus, so I started with a systematic reanalysis of septal region efferent connections (axonal projections) in rat. The ARGM required microinjecting a small volume of pathway tracer (³H-amino acids) into a brain region of interest, and early studies in the Cowan group used relatively large volumes (0.5–1.0 µl) for preliminary studies. With the injection method developed earlier for behavioral experiments, I could now deliver tracer in a volume of about 20 nl, which allowed for much more precise localization of injection sites to the tiny subdivisions of the septum and other brain parts.

The analysis of septal projections soon expanded to include the interrelated hippocampal formation at the cortical level, and the hypothalamus subcortically. The result was a series of long papers between 1975 and 1979 in the Journal of Comparative Neurology, of which Cowan was editor at the time, that provided a wealth of new information on the highly interconnected “hippocampal-septal-hypothalamic” system. The hypothalamic part of the project was spearheaded in rat, cat, and monkey by a brilliant medical doctor–doctoral student, Clif Saper, who went on eventually to chair the Department of Neurology at Harvard’s Beth Israel Deaconess Medical Center for almost 30 years and who made outstanding contributions to our understanding of neural mechanisms controlling the sleep-wake cycle, thermoregulation, and many other components of autonomic regulation.

Three aspects of this work were particularly interesting and showed the power of the new methodology. First, contrary to a century of conventional wisdom, we found that the fornix, which ends in the mammillary body and anterior thalamus, does not originate in the hippocampus; instead, it arises in obscure retrohippocampal cortical fields including the subiculum and presubiculum. We first presented this novel finding in 1974 at a symposium where no one else mentioned finding similar results (Swanson and Cowan, 1974), prompting us to dash off a report to Science (Swanson and Cowan, 1975). Second, we discovered the efferent projections of the tiny suprachiasmatic nucleus (Swanson and Cowan, 1975), which had been shown recently to receive a direct input from the retina and to be the long-sought circadian rhythm generator. Third, the first detailed parcellation and connectional analysis was carried out for the preoptic region of the hypothalamus (Swanson, 1976).

Focus on the Paraventricular Nucleus as an Ingestive Behavior Hub

One day in 1974 Cowan got a phone call from a colleague in the Biology Department, Rita Levi-Montalcini, who, along with Stanley Cohen, would win the Nobel Prize 12 years later for their discovery and characterization of nerve growth factor (NGF). At the time of the call, she was moving back to spend most of her time at a lab in Rome but had just received word that an approved grant whose funding was on hold, unexpectedly had been activated. She asked if Cowan knew anyone who would be interested in coming to the other campus to work on the grant and spend the windfall. Luckily, Max asked me, and I readily agreed. My plan was to spend half my time doing the circuit analysis work with him, and the other half working on Rita’s project, which was actually quite interesting. She had discovered that NGF microinjections into the locus ceruleus (a tiny brainstem nucleus with only noradrenergic neurons, almost reminiscent of a sympathetic ganglion) induced the sprouting of peripheral sympathetic axons into the brain, toward the injection site. The aims of the grant were to characterize this ectopic ingrowth of neurotransmitter-specific axons, presumably from the superior cervical ganglion.

My initial concern was to distinguish between ingrowth from the periphery, and possible ingrowth from the central noradrenergic system, which had been so elegantly discovered and described by Dahlstöm and Fuxe (1964) with the Falck-Hillarp histofluorescence method for biogenic amines. No one at Washington University was using the method, which required specialized equipment and skills, and painstaking controls to distinguish between dopamine, noradrenaline, and adrenaline. As an alternative, I approached Boyd Hartman in the Psychiatry Department, who while working with Sidney Udenfriend at NIH had published the first paper to apply immunohistochemistry to central nervous system tissue (Hartman and Udenfriend, 1970). For this, they first purified bovine dopamine ß-hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine, and then used a specific antiserum to the protein as a marker for noradrenergic (and adrenergic) neurons. Boyd became not just one of my most valued collaborators but also one of my closest friends; he did not enjoy reading the literature, preferring instead to think originally and talk sensibly about any topic that came up.

Early immunohistochemical methodology was difficult also, but we managed to cut multiple series of cryostat sections through the length of the rat brain and to produce a complete account of the central adrenergic system—the first brainwide atlas of a neurotransmitter-specific system with immunohistochemistry (Swanson and Hartman, 1975). The technical experience and knowledge we gained soon proved invaluable in another context. However, experiments with Rita to retrogradely label the region where she had made her injections (locus ceruleus) with ¹²⁵I-NGF injected into the hippocampus proved fruitless, although, interestingly, we instead found retrograde labeling in the medial septal complex, which we knew from autoradiographic experiments projects to the hippocampus, and other evidence suggested was cholinergic. Unfortunately, or fortunately, as a last-minute control, I injected free ¹²⁵I into the hippocampus and also got retrograde labeling in the medial septum. The radiolabeled NGF I had obtained from Ralph Bradshaw in the Department of Biological Chemistry hadn’t been cleaned up properly, and I never got a publication with Rita.

In 1975, we were generating material and beginning our analysis of hypothalamic projections, using as an initial guide the authoritative review by Nauta and Haymaker (1969), who had concluded, based on the older generation of degeneration methods, that the hypothalamus influences behavioral and visceral functions by a series of short descending connections through the reticular formation. But this view was shattered in a conceptually simple experiment by Kuypers and Maisky (1975) who used the new generation of axonally transported retrograde pathway tracers (horseradish peroxidase, HRP) to show that in cat the hypothalamus projects directly all the way to the spinal cord. It was not possible, however, in their brief report to determine which medial hypothalamic neuron groups were labeled.

I immediately began injecting HRP in the rat thoracic spinal cord and discovered that a major site of retrograde labeling was the paraventricular hypothalamic nucleus (PVH). On a visit to Cowan’s office, I also found Saper and another colleague, Arthur Loewy, there, and they were discussing having done the same experiments in monkeys and cats, with similar results. Furthermore, we had found autoradiographically that injections spreading to include the PVH generated anterogradely-labeled descending projections to the dorsal vagal complex (parasympathetic) and spinal intermediolateral column (sympathetic). We immediately teamed up to write a paper on our joint findings (Saper et al., 1976), which suggested a general connectional feature of mammals, and which played a seminal role in the future of each of our careers.

For me, this was an “aha moment” because three different findings came together. First, there was my thesis finding of a periventricular ingestive behavior hot spot centered near the PVH. Second, there was the observation from our DBH mapping study confirming that the PVH has perhaps the densest noradrenergic terminal field in the brain. Third, there was evidence from Dick Gold (1973) that the “hypothalamic feeding center” was not in the ventromedial nucleus, as conventionally assumed, but instead was associated with a part of the central (nor)adrenergic system dorsomedial to the ventromedial nucleus, presumably in the PVH. Interestingly, my inspiration, Pete Grossman, began following up Gold’s work with a graduate student, Joe Kelly, and for his postdoctoral work, he came to Washington University to work with Boyd Hartman. As a side project with me, he found a variety of previously unreported oxytocinergic or vasopressinergic neuron populations that project to the posterior pituitary with the retrograde tracer HRP (Kelly and Swanson, 1980). Tragically, less than a year after the paper was published, Joe died of a metastasizing osteosarcoma of the leg, cutting short the very promising research career of one of the nicest people I have ever known.

Thus began an intense dissection of the PVH over 30 years that eventually resulted in the publication of approximately 40 papers. It was already well known that the PVH, along with the supraoptic nucleus, are the main sources of axons to the posterior pituitary that release oxytocin and vasopressin into the general circulation. Using immunohistochemistry, I initially showed that at least part of the PVH descending projection to the dorsal vagal complex used one or the other of these neuropeptides (Swanson, 1977), and that there was an ascending noradrenergic projection from the dorsal vagal complex to the PVH (Swanson and Hartman, 1980), providing a potential circuit substrate for autonomic-neuroendocrine coordination.

The next step was to determine whether PVH projections to the pituitary gland, dorsal vagal complex, and spinal cord arise from the same, or from different, neuron population(s). Hans Kuypers in Rotterdam had moved beyond HRP to develop a rapid method for determining axon collateralization patterns with multiple retrogradely transported fluorescent tracers. I wrote to him asking for tracer samples, which he kindly sent, and after testing them, I was unimpressed with results that involved huge injection sites and rather poor sensitivity. I wrote again asking for advice, and amazingly, he instead invited me to his lab to use the even better tracers they had developed in the meantime. This was even more amazing from a personal perspective because his mentor, Walle Nauta, and my mentor, Max Cowan, were intense, world-class rivals. They both worked on the connections of essentially the same parts of the brain with the Nauta degeneration method, but now Cowan had developed the autoradiographic tracing method that rendered Nauta’s degeneration method obsolete overnight.

I spent the summer of 1979 in Kuypers’s lab, and it was the single most productive episode in my research career. I learned the methodology from Marina Bentivoglio, who was instrumental in developing it, along with Derek van der Kooy who had just left for Toronto. And Kuypers himself worked out a transpharyngeal surgical method for injecting tracer into the rat pituitary gland. The results laid the groundwork for all subsequent research on the PVH: in rat, three topographically (and functionally) distinct neuron populations project to the lower brainstem and spinal cord (autonomic, and as inferred later, behavioral control), to the posterior pituitary (magnocellular neuroendocrine system), and to the median eminence (parvicellular neuroendocrine system) (Swanson and Kuypers, 1980; Swanson et al., 1980). Neely and I remained friends with Hans until his untimely death several years later, after he had moved on to Cambridge as chair of the Department of Anatomy.

At summer’s end, we returned to St. Louis, and in September, my first postdoc arrived—from Dick Gold’s lab—Paul Sawchenko, whose thesis work focused on the role of the subdiaphragmatic vagus nerve in hypothalamic hyperphagia and obesity. An obvious question now concerned the organization of ascending noradrenergic pathways, with vagal sensory inputs in the medulla and PVH subdivisions at the other end, especially in light of convincing recent evidence from Sarah Leibowitz (1978) at the Rockefeller University that the PVH is the most effective site for norepinephrine-elicited eating (and drinking). To approach the problem, though, Paul spent the first six months developing and meticulously validating a method combining the most sensitive of Kuypers’s retrograde tracers with immunohistochemistry for any desired neuronal antigen (Sawchenko and Swanson, 1981).

In the meantime, Cowan had accepted a position at the Salk Institute in La Jolla, and he invited several younger colleagues at Washington University to be independent members of his “mega-lab” there, including David Amaral, Dennis O’Leary, Brent Stanfield, and myself (after Tom Woolsey had turned down the offer). On one hand, it was an easy offer to accept: I had always wanted to get back to California, and the Salk was a superb and exciting place to do neuroscience research. But, on the other hand, Neely and I had a wonderful life in St. Louis and had made many friends. Our son, Reid (our pride and joy), was born there in 1977, I got my first NIH grant the next year, and the year after that, I got a tenure-track position in Cowan’s Department of Anatomy and Neurobiology, with the proviso I teach gross anatomy to the medical students. It was a course I had never taken, and dreaded, but now in hindsight am grateful I suffered through—the insight into how the body works has been invaluable. Smelling of formaldehyde for two years was a small price to pay, although Neely might have disagreed.

Salk Institute, CRH Neuron, and Molecular Switching Hypothesis

Not only was my earlier acquaintance from Pomona College, Francis Crick, at the Salk Institute in 1980 but also, and more tantalizing for our research, so were Roger Guillemin, who had won the Nobel Prize in 1977 for his characterization of hypothalamic peptide neurotransmitter-neurohormones controlling the anterior pituitary, and Wylie Vale, his former student and colleague who recently had split off to form his own lab. They were in a heated race to characterize the elusive hypothalamic “corticotropin releasing factor” that controls anterior pituitary ACTH release, and thus adrenal corticosteroids that regulate blood glucose levels, especially during stress. It was as intense as the earlier “Nobel Duel” between Guillemin and Andrew Schally for the first hypothalamic releasing factors (Wade, 1981).

After we arrived, Paul spent about a year finishing the analysis of ascending noradrenergic projections to the PVH, which was published in Science (Sawchenko and Swanson, 1981). We then spent another year characterizing, to the extent possible, the putative neurotransmitter content of all known inputs of the PVH as well of the different PVH neuron types with projections to the dorsal vagal complex and spinal cord.

Four general principles emerged from this work, which we summarized in the Annual Review of Neuroscience (Swanson and Sawchenko, 1983). First, neural inputs to the PVH are quite diverse; there are several dozen, and they are widely distributed in the brain. Second, every source of these neural inputs ended in more than one PVH subdivision, usually in a unique pattern. Third, every projection we examined that ended in the magnocellular PVH subdivision also ended in the supraoptic nucleus. And, fourth, PVH neurons with descending projections to the dorsal vagal complex and spinal cord may express multiple neuropeptides.

In the meantime, there was another breakthrough: Vale’s group beat out Guillemin’s group in fully characterizing “corticotropin releasing factor” (Vale et al., 1981), which could then be called corticotropin releasing hormone (CRH). Specific antisera allowed cellular localization of the 41-residue neuropeptide, and preliminary immunohistochemical mapping in rat by Floyd Bloom suggested that the neuroendocrine CRH neurons were localized to the “medial anterior parvocellular region” of the PVH (a feature that immediately caught our attention because of the established role of the PVH in eating behavior). In addition, they reported the existence of several intrahypothalamic axon tracts and one group of axons entering the midbrain medial longitudinal fascicle (Bloom et al., 1982).

To characterize the PVH distribution more carefully, we began a detailed mapping study that instead identified immunoreactive neurons and fiber tracts divided into three broad parts throughout the brain (Swanson et al., 1983). The first part consisted of CRH neurons distributed through all PVH subdivisions but concentrated in the dorsal medial parvicellular part, combined with a dense axon bundle from the PVH to the median eminence. This PVH-median eminence projection was the only one we detected in which immunoreactivity clearly increased after adrenalectomy, which removes glucocorticoid negative feedback on the brain. The second part consisted of neuron groups and interconnected fiber systems stretching from the amygdala to the medulla and associated most closely with the limbic system and autonomic control mechanisms. And the third part consisted of interneurons concentrated in layers two and three of the cerebral cortex. The results suggested that central CRH systems are involved in controlling both neuroendocrine, autonomic, and perhaps behavioral and cognitive responses to stress.

Further studies revealed that PVH parvicellular neuroendocrine CRH neurons also express vasopressin following adrenalectomy (Sawchenko et al., 1984), which was independently reported by four other groups (reviewed in Swanson, 1991). We then went on to show that each of the three different structure-function PVH neuron populations express a remarkable variety of neurotransmitter peptides—at least eight in CRH parvicellular neuroendocrine neurons; that at least three of the same neuropeptide genes (CRH, vasopressin, and angiotensin II) are expressed in each of the three distinct neuron types; and that glucocorticoid hormones differentially regulate the expression, and thus, ratios of these three common neuropeptides in the three neuron types (Swanson, 1991). The CRH parvicellular neuroendocrine neuron itself provided the prototype for a uniquely complex neuron type: one with neurotransmitter, paracrine, and endocrine functions mediated by different compartments of its axonal tree, and one in which the ratio of neuropeptides varied with endocrine status (Swanson et al., 1987).

In the end, this analysis of the PVH provided a clear circuit model for the hypothalamic integration of autonomic, neuroendocrine, and behavioral mechanisms in the control of motivated or goal-oriented behavior, using ingestive behavior as an example. The analysis also suggested that when neurons express more than one neurotransmitter and have axon collaterals to more than one site, then changes in the ratio of those neurotransmitters might lead to the molecular (chemical or biochemical) switching of information flow through an otherwise structurally unchanged circuit. This was a molecular switching of information flow hypothesis that also suggested a mechanism for transient “silent synapses” (Swanson and Simmons, 1989; Swanson, 1991, 1992a, 1996).

HHMI, Transgenic Mice, and the Promoter-Transcription Factor Craze

The phenomenon of neurotransmitter expression plasticity naturally led to the question of underlying molecular mechanisms (Swanson, 1983), and an opportunity to explore this emerging field soon emerged. In 1983, Vale’s group had characterized rat hypothalamic growth hormone-releasing hormone (GRH), and using their antibodies, we had mapped the brain distribution of this neuropeptide, including its neuroendocrine neurons, which are in the hypothalamic arcuate nucleus rather than the PVH (Sawchenko et al., 1985). At about the same time, Ron Evans at the Salk and Geof Rosenfeld at UCSD were teaming up to examine regulation of growth hormone gene expression, which is restricted to anterior pituitary somatotropes in the normal adult rodent body.

Their most spectacular result was the creation of extremely large mice, by using a hybrid transgene containing the structural part of the growth hormone gene driven by a “super” promotor from the metallothionein-I gene, resulting in abnormally high levels of growth hormone during development. The adults could be almost twice the normal body weight (Palmiter et al., 1982). These “supermice” even captured public attention to the extent that somewhat tongue-in-cheek editorials appeared in the New York Times and Washington Post. Late-night television icon Johnny Carson devoted much of one of his nightly monologues to an hilarious analysis of possible repercussions (Myelnikov, 2020).

Collaboration with Ron and Geof was an obvious opportunity—combining their molecular interests and experience with our structure-function interests and experience. One of our first projects together established the principle that fusion genes with multiple promotor regions can display novel expression patterns that differ from the endogenous expression patterns of either part of the fusion gene alone (Swanson et al., 1985). Our example was the growth hormone-metallothionein fusion transgene: neither growth hormone nor metallothionein-I are expressed in the normal brain, but in transgenic mice, the fusion gene was expressed in specific sets of brain neurons, with the highest expression levels, remarkably, in the PVH and supraoptic nucleus.

Another early project involved characterizing the nervous system expression pattern of a novel neuropeptide, ⍺-CGPR, which is expressed by tissue-specific alternative splicing of mRNA from the “calcitonin gene” into either calcitonin or ⍺-CGRP (Rosenfeld et al., 1983). This was followed up with the discovery of a second gene that encodes ß-CGRP, a peptide differing from ⍺-CGRP by a single amino acid residue, and the finding that the brain spatial distribution of the two peptides is remarkably similar qualitatively, but with strikingly different expression levels in each locus. This work was led by a remarkably talented graduate student, Susan Amara (Amara et al., 1985), who went on to a distinguished career in research at Yale and the Vollum Institute, and in administration at the National Institute of Mental Health (NIMH).

These two projects had important side effects. Experimentally, they led us to develop in situ hybridization methods with Jeff Arriza, one of Evans’s students, and Donna Simmons, my very experienced, hard-working, and innovative lab manager—who eventually published what became the standard protocol for in situ hybridization in the nervous system (Simmons et al., 1989). Conceptually, they led to one of the first reviews of transgenic animal use for the study of development and models of human disease (Evans et al., 1985). And practically, these projects led to Ron, Geof, and I being appointed Investigators of the Howard Hughes Medical Institute (HHMI) in 1985, about a year after Sol Snyder had tried to recruit me to an HHMI position at Johns Hopkins. Around this time, Ron and Geof agreed to concentrate on their individual research interests, and my lab collaborated with Geof on a number of projects involving GRH and prolactin transgene expression and its spatial localization—and on the brainwide distribution during development and in the adult of a large new family of homeodomain regulatory genes (He et al., 1989; Alvarez-Bolado et al., 1995). Several of these POU-domain transcription factors turned out to have dynamic expression patterns from the earliest stages of PVH and supraoptic nucleus development, but it remained for others to demonstrate their critical roles (reviewed in Swanson, 2009).

PHAL: A Powerful New Anterograde Pathway Tracer

As I began collaborating with Evans and Rosenfeld, Paul established his independent research program, focusing on CRH and its central mechanisms of action, and eventually was named the inaugural Wylie Vale Chair at the Salk, fitting recognition for his distinguished research career. But early on, he teamed up with Charles (Chip) Gerfen, who had come from completing his doctoral work in Ronald Clavier’s lab at Northwestern University to work with Cowan on the chick visual system. Chip and Paul embarked on a gamble to find a better anterograde pathway tracing method than autoradiography, which avoided the axon-of-passage problem, but was difficult to interpret because projection patterns were inferred from silver grain patterns over histological sections. Chip had experience with the new wheat germ agglutinin-HRP bidirectional pathway tracer, but axonal labeling was “fuzzy”—not nearly as crisp as the immunohistochemical labeling Paul showed him for vasopressinergic or oxytocinergic axons—and it involved axons-of-passage. On a hunch, they screened other plant lectins and hit the jackpot: Phaseolus vulgaris leucoagglutinin (PHAL).

In a model of careful validation (Gerfen and Sawchenko, 1984), they established that, following their protocol, PHAL is transported only anterogradely in axons; that it is virtually never taken up and transported by axons-of-passage; that axons and their collaterals are labeled with the clarity of Golgi preparations; and, as we now know, that it is about an order of magnitude more sensitive than the autoradiographic method in detecting axonal projections. In collaboration with Chip, we published the first experimental paper using PHAL to trace central pathways (Swanson et al., 1984). First, we established with PHAL (and the retrograde tracer True blue) the structural existence of a direct pathway from the substantia innominata (ventral pallidum) and lateral preoptic area to the “mesencephalic locomotor region,” and then our wonderful Canadian colleague Gordon Mogenson (whose book, The Neurobiology of Behavior: An Introduction, 1977, was invaluable to my thinking) confirmed the monosynaptic nature of the connection electrophysiologically, showing a roughly equal proportion of excitatory and inhibitory responses. For anterograde pathway tracing in rats, the autoradiographic method was the method of choice for a dozen years; since 1984, the nongenetic method of choice has been PHAL.

From Ingestive to Reproductive, Agonistic, and Behavioral State-Motivated Behavior Circuits

During our decade at the Salk, I balanced Vale, Evans, and Rosenfeld collaborations with ongoing work on circuitry related to motivated behaviors. The first immigrant to our Salk lab was a doctoral student of Roger Gorski, the well-known UCLA behavioral neuroendocrinologist who had discovered the “sexually dimorphic nucleus of the preoptic area” in rat (Gorski et al., 1978). The student was Richard (Rich) Simerly, and after hearing a talk I gave at UCLA in 1981, he wanted to apply our methodology and thinking about the ingestive behavior circuit to Gorski’s sexually dimorphic nucleus and to what (due in no small part to his own work) would become known as the sexually dimorphic circuit in rodents. He made the drive between Los Angeles and the Salk countless times for his thesis work, and later as a postdoctoral fellow in the lab. His determination and creativity paid off with 21 papers from our collaboration (see Simerly, 2002).

Some highlights of his work include a PHAL analysis of projections from the medial preoptic nucleus, which includes Gorski’s nucleus (Simerly and Swanson, 1988), and identification and detailed structural characterization of the anteroventral periventricular nucleus, a tiny sexually dimorphic nucleus in the preoptic region that controls the estrous cycle (e.g., Simerly et al., 1985). He also demonstrated that naturally occurring changes in estrogen levels during the estrus cycle change the ratio of neuropeptide gene expression in specific neuron populations of the sexually dimorphic circuit (Simerly et al., 1989), supporting the molecular switching of information flow hypothesis mentioned earlier for the PVH and the ingestive behavior system.

As an interesting aside, while this work on the rat sexually dimorphic circuit was progressing, the lab next door was occupied by the visual system neuroscientist Simon LeVay, who had established his reputation working with Torsten Wiesel and David Hubel at Harvard. Unfortunately, there was no communication between the two labs, so we were stunned to see Simon’s famous paper appear in Science (LeVay, 1991)—claiming that one of four sexually dimorphic preoptic nuclei differs between presumably heterosexual and homosexual men, and that the one preoptic nucleus that differs in homosexual men is roughly equivalent in size to the presumably heterosexual female preoptic nucleus.

LeVay had been deeply affected by the AIDS epidemic and decided to abandon the visual system for the human hypothalamus, with a neuroanatomical study suggesting that human sexual orientation has a biological substrate. With that, he left academic science and transitioned into an author of scientifically balanced, popular books on gender identity and related topics. It was at that point, after the dust had settled, that we became friends, reconnecting in Los Angeles at a small cocktail party arranged by Neely for Luc Montagnier, who would go on to share a Nobel Prize for his discovery of the human immunodeficiency virus.

Next came Wally Lind (1982) from Kim Johnson’s lab at the University of Iowa, Christer Köhler and Lena Haglund (1983) from Sweden, and Dennis Brittain (1984), my only graduate student in San Diego. Wally’s thesis work had been on the role of the subfornical organ in drinking induced by circulating angiotensin-II, and he went on with us to characterize central projections of the subfornical organ with PHAL (Swanson and Lind, 1986) and to describe with immunohistochemistry the whole central angiotensin-II system (Lind et al., 1985), including an angiotensinergic subfornical organ to PVH connection (possibly explaining the angiotensin-induced drinking I had explored in my own thesis), and the dynamic expression of angiotensin-II in PVH neurons under the influence of glucocorticoids (Swanson et al., 1987). Unfortunately, Wally became discouraged with the slow pace of a research career and left to try his hand at creative writing.

Christer and Lena worked on the hypothalamus and hippocampus, most notably with the PHAL method. Lena described in detail the projection from the supramammillary nucleus to the hippocampal formation (Haglund et al., 1984); and Christer and I made the startling discovery that the lateral entorhinal area projects to the entire cerebral cortical mantle (Swanson and Köhler, 1986). Christer went on to a distinguished career in big pharma and Lena, a medical doctor, headed a medical branch in Strängnäs, about 60 miles from Stockholm.

Dennis did a superb PHAL analysis of complex brainwide projections from the infralimbic area of prefrontal cortex, using a Nikon Magiscan image analysis and mapping system. His valuable thesis (Brittain, 1988) was never published as a journal article, however, and he left science for an engineering startup.

In 1984, we also saw the arrival of Alan Watts and his bride, Graciela Sanchez-Watts. At my request, Neely found the two of them a tiny studio apartment near the beach. Imagine her horror when she went to pick them up. After waiting for quite a while for them to appear, she located a pay phone (there were no cell phones at the time) and called to say that no couple with lots of luggage had gotten off any of the trains. It was then that I told her that maybe they were waiting at the trolley stop because they were coming in from Mexico. Oh, and by the way, they had a baby with them. Finally finding them, Neely was furious (at me, not at them). The “baby,” Kathya, was 12 years old (from Graciela’s previous marriage), and Neely was taking them to a tiny studio apartment barely large enough for two, let alone three. Despite my gaff, we remain colleagues and friends to this day, and still laugh about the first meeting. Alan is a now a professor of Biological Sciences at USC (in the lab next to mine), and Graciela is a research associate; she is a superb histologist specializing in immunohistochemistry and in situ hybridization and is the Watts lab manager.

Alan had trained in neuroendocrinology with George Fink at Oxford, where Graciela was a radioimmunoassay technician. For his thesis, Alan examined the effects of lighting schedules and gonadal steroid hormones on luteinizing hormone release from the anterior pituitary and was now interested in hypothalamic circuitry controlling cyclical luteinizing hormone release. For this he, Graciela, and I began with a careful reexamination of projections from the suprachiasmatic nucleus, because of its obvious role in the behavioral state system as the endogenous circadian rhythm generator and entrainer. A combination of PHAL and retrograde tracer-immunohistochemical methods was used (Watts et al., 1987; Watts and Swanson, 1987), and one finding stood out in particular. By far the densest terminal field was in what we named the subparaventricular zone, which stretched dorsally near the third ventricle and then arched below the PVH, and which, it turned out, generates basically the same output pattern as the suprachiasmatic nucleus itself only stronger—perhaps acting as a second-stage differentiating amplifier. He also demonstrated a natural diurnal rhythm of preproCRH mRNA in PVH neurons that correlates with daily fluctuations of corticosterone, providing another example of neurotransmitter expression plasticity influenced by steroid hormones (Watts and Swanson, 1989a). Finally, he developed and validated a combined in situ hybridization-immunohistochemistry-double retrograde tracing method that was applied to PVH projections to spinal cord and median eminence in the same animal (Watts and Swanson, 1989b).

The next big arrival, in 1987, was special indeed: Ju Gong from Xi’an, who four years later in 1991 would be the first neuroscientist elected to the Chinese Academy of Sciences. I had met Ju in 1984, when I spent a month at the Peking Union Medical College under the sponsorship of the World Bank, which was evaluating Chinese institutions of higher education for major investment. My assignment was quite vague, and upon arrival, I was surprised to learn that I would be teaching a neuroanatomy course to about 50 professors from 23 universities around China. My second surprise was discovering that after my lecture, in English of course, it was repeated in Chinese by one of the professors—Ju Gong, whose delivery of the material was much better than mine! After the course was over, Ju invited us to his university and accompanied Neely and me to Xi’an on the 24-hour train, an unforgettable adventure. It turned out that he had grown up in Shanghai, the son of influential international publisher parents, and his English, and knowledge of American culture, were astonishing. Choosing to continue his medical training in China rather than fleeing to Taiwan with his parents, his career path seemed assured until the arrival of the Cultural Revolution in 1966. Forced to train uneducated peasants in the countryside to become physicians cut short the promise of an international research career. It wasn’t until the end of this period that he was able to resume his research, losing more than 15 precious years in the process.

Ju had done the first study in China with the Nauta degeneration method in 1965, but to retool after the Cultural Revolution he did two sabbaticals, first with Tomas Hökfelt (1985–1986) at the Karolinska Institutet, and then with us at the Salk, where his project involved a then obscure part of the septal region called the bed nuclei of the stria terminalis (BST), which was known to receive a massive input from the amygdalar region. Ju used an insightful combination of cytoarchitectonic and chemoarchitectonic analyses to parcel the BST into about a dozen distinguishable nuclei and areas (Ju and Swanson, 1989; Ju et al., 1989), which laid the groundwork for a rational attack on their projections. I asked Ju to send me a student to carry out this project, which he promised to do when the right one came along.

The last postdoc coming to the lab in La Jolla (1988) was Newton Canteras, a medical doctor–doctoral graduate who had studied in São Paulo with Juarez Ricardo, a student of Nauta’s who discovered in rat the ascending projections of the nucleus of the solitary tract to the hypothalamus (including the PVH) and endbrain. Newton’s first project was to characterize with PHAL the brainwide projections of the posterior amygdalar nucleus (Canteras et al., 1992) and adjacent ventral subiculum (Canteras and Swanson, 1992), which end massively in restricted hypothalamic nuclei. Their significance for motivated behavior control circuits—and specifically those related to defensive–agonistic behaviors—became clear later.

Although our research was advancing quickly, all was not well. In the last half of the 1980s my impression was that the research leadership at HHMI, and a few of the younger, influential professors at the Salk, projected an air of disdain for anything other than molecular neuroscience. Cowan, in his new role as chief scientific officer at the HHMI, even suggested directly that I “become a molecular biologist,” as he had done in an administrative way, while dismissing his earlier career as a neuroanatomist. Cowan had gained the political power he had long aspired to and wielded a heavy stick against those who did not follow his lead—I was caught in the crosshairs. I enjoyed synergistic collaboration with the molecular biologists, and used their tools, but my core research interests were too deeply rooted in systems neuroscience. So, around 1988, I began exploring possible moves to UCLA and USC.

Then I got a phone call from Richard F. (Dick) Thompson, whose groundbreaking textbook I had used in college, and who was working out the neural circuit for Pavlovian learning in mammals (Thompson, 2013). He had been recruited from Stanford, where he served as chair of the Human Biology Program, to USC, and had just been appointed director of its unique Program in Neural, Informational, and Behavioral Sciences (NIBS), complete with a new research building. With this innovative, university-wide blend of neurobiology, computer science, and psychology, USC had a stated goal of being number one in U.S. neuroscience by the mid-1990s (Barinaga, 1988). Thompson wanted me to join the mix of new recruits. After protracted negotiations I accepted USC’s generous offer, and with mutual disaffection, parted ways with the HHMI, crystallized by a personal talk at one of the HHMI research meetings with Paul Greengard (an HHMI investigator and senior advisor) in Bethesda. He knew I was uncomfortable and asked if I wanted to continue with the HHMI; I said no, and the final decision was then made for me.

Although our son Reid had a wonderful time growing up in the San Diego area, Neely and I loved Los Angeles and were excited to move to Manhattan Beach in the summer of 1990. During the next decade, the NIBS Program had great success (though never reaching number one), but by 2007, new administrations had lost interest and the provost (Max Nikias) and dean of the college (Howard Gilman) dissolved what was left of the NIBS Program to the dismay of most neuroscientists around the university.

Move to USC and a Long-Term Plan

The transition from San Diego to Los Angeles was relatively easy because a key group decided to move with me to the brand-new USC lab: Donna Simmons, Newton Canteras, and Dave Warren, my superb administrative assistant. Graciela Sanchez-Watts and Alan Watts came a year later, with Alan holding an independent tenure-track position and Graciela working as a research associate in his lab. Since then, Alan’s lab has focused on neural mechanisms underlying eating behavior and the control of blood glucose levels.

I took the opportunity during the moving process to reevaluate my research priorities and to develop a long-term plan that was buffered by a generous annual research fund as part of my recruitment package. The plan was simple and based on what I was most interested in and on what I was best at. The strategy was to finish a systematic examination of rat amygdalar-septal-hypothalamic circuit organization with the PHAL method (or a better one if it came along)—with the expectation of revealing basic organizing principles in the circuitry controlling different classes of motivated behavior. In essence, we would use the model developed for the PVH and ingestive behavior to uncover circuits underlying expression of the two other classes of motivated behavior common to all animals: reproductive (sexual and parental) and defensive/agonistic (fight or flight).

My first project was to finish and publish the rat brain atlas I had begun working on in 1974 at Cowan’s suggestion. It had taken years of trial and error to find a suitable histological methodology, but finally, celloidin embedding was chosen, and at the Salk, I cut, Nissl-stained, and mounted serial transverse sections of the brain to be used for the atlas. Evans and Rosenfeld saw what I was doing and quipped that I was generating a library of brain sections, analogous to the genomic libraries they were generating. Then I photographed a selection of 73 levels on 4” x 5” negatives that were used for making prints on 16” x 20” sheets of photographic paper. In hindsight, it was fortunate the project had dragged on so long: Adobe Illustrator was first released in 1988, and I used it to create the atlas-level map that accompanied each atlas-level photomicrograph.

Elsevier, under the editorial guidance of Nello Spiteri, did a wonderful job of publishing Brain Maps: Structure of the Rat Brain (Swanson, 1992b), hardbound in oversized format, on thick paper. It had several unique and useful features. First, there was a complete, internally consistent terminology hierarchy, with annotations to the primary literature covering all structures in the hierarchy. Second, there was a foldout flat map of the central nervous system, analogous to Mercator’s wall map of the globe. It was, in essence a fate map of the two-dimensional neural plate, and allowed for the display of any and all connections (crossed or uncrossed) on a single template. Third, all maps were provided in vector graphics format (Swanson, 1993) so any type of spatial data from our lab, or any other lab, could be plotted and displayed on standard reference templates, making comparisons between datasets easy, and simultaneously eliminating the need to make new pen and ink drawings for each experimental brain to be published.

These features proved invaluable when neuroinformatics began taking shape a few years later. And they were complemented and expanded when Gonzalo-Alvarez Bolado and I created a companion atlas, Developmental Brain Maps: Structure of the Embryonic Rat Brain (Alvarez-Bolado and Swanson, 1996), which grew out of our experience mapping developmental expression patterns of the POU-III homeobox gene family (Alvarez-Bolado et al., 1995) mentioned earlier.

Comprehensive Analysis of Connections and Circuits

Newton Canteras provided continuity between the Salk and USC in this domain. He went on to publish detailed accounts of projections from the medial amygdalar nucleus, ventromedial hypothalamic nucleus, and dorsal and ventral premammillary nuclei (see Swanson, 2000a), being the first to plot and publish his PHAL results on the new digital atlas (Canteras et al., 1992). On returning to the University of São Paulo, where he is now a professor in the Institute of Biomedical Sciences, he carried out a series of experiments involving exposure of a rat to a natural predator (cat), eliciting an innate defensive behavioral response, and examining the brain for increased Fos levels. Luckily, many of the Fos-labeled hypothalamic nuclei were interrelated by connections he had been studying with PHAL, and one region in particular stood out as the most heavily labeled: the obscure dorsal premammillary nucleus. When it was lesioned with ibotenic acid, the defensive behavioral response was eliminated (Canteras et al., 1997). These early findings by perhaps my most creative student-collaborator stimulated a large body of ingenious and pioneering research on the brain circuitry mediating defensive and other agonistic behaviors (see de Lima et al., 2019).

The first new additions to the USC lab were three outstanding doctoral students, Richard H. (Rick) Thompson in 1990, and Gorica Petrovich and Eleni Markakis in 1991. With respect to circuit analysis, Rick accomplished three main things as a graduate student and later as a postdoctoral fellow. First, he characterized in great detail the neural outputs and inputs of the dorsomedial hypothalamic nucleus (see Thompson and Swanson, 1998). Then he recognized and analyzed with PHAL the interconnections of a visceromotor pattern generator network in the periventricular hypothalamus, with the dorsomedial nucleus being its predominant node (Thompson and Swanson, 2003). Finally, he developed and validated a sophisticated double coinjection method for identifying chains of interconnected regions. Each injection was a mixture of an anterograde and retrograde tracer, and he used the method to define the neural system in which a tiny dorsomedial nucleus accumbens “hedonic hot spot” for eating behavior is embedded (Thompson and Swanson, 2010).

Gorica tackled the exceptionally difficult problem of subsystem organizational principles in the myriad of connections between the amygdalar region, hippocampal formation, and hypothalamus (Petrovich et al., 2001). As a postdoc with Dick Thompson and me, she followed up on the molecular switching of information flow hypothesis. Using in situ hybridization, Gorica demonstrated a conditioned increase in enkephalin (but not other neuropeptide) mRNA levels within neurons of the central amygdalar nucleus after rats were placed in an environment they associated with an unpleasant experience. She went on to study forebrain mechanisms of hunger control and is now a professor of psychology at Boston College.

Eleni came from Margaret (Peggy) Hollyday’s developmental neuroscience lab at Bryn Mawr where she was involved in studies of chick spinal cord motoneuron pools. With us, Eleni carried out a detailed, global analysis of neuroendocrine motoneuron developmental birthdates with a combined BrdU-immunohistochemical-retrograde tracing methodology she developed (Markakis and Swanson, 1997).

Pierre-Yves Risold came to the lab in 1991 as a postdoctoral fellow after working on the localization of hypothalamic peptides with Claude Bugnon and Dominique Fellmann at the Université de Franche-Comté in Besançon. He and Canteras began by performing a detailed PHAL analysis of projections from the various parts of the anterior hypothalamic nucleus (Risold et al., 1994), long implicated in agonistic behavior, but then switched to a conceptually important reexamination of subsystem interactions between the hippocampal formation, septal region, and hypothalamus. The results, which were first summarized in Science (Risold and Swanson, 1996), showed how different domains in hippocampal fields CA3 and CA1 project upon a new parceling scheme for the lateral septal nucleus, which then shares bidirectional connections with various subsets of hypothalamic nuclei with identified functional attributes. The details of this new way of looking at functionally specialized hippocampo-septal-hypothalamic subsystems were published in two monograph-style articles (Risold and Swanson, 1997a, 1997b) and led Pierre to then perform more experiments and summarize the literature on the overall relationship between the hypothalamus and cerebral cortex (Risold et al., 1997). Pierre is now an associate professor at the Université de Franche-Comté in his hometown of Besançon.

Hong-Wei Dong, a young medical doctor (and doctoral candidate) arrived in 1997 from Xi’an, where he was trained by Ju Gong. Recall that 10 years earlier I had asked Ju to send me a student to work on BST connections, and Ju had finally found the right match. Hong-Wei was worth the wait. He spent about six years on a meticulous PHAL analysis of BST projections to the rest of the brain that resulted in eight long papers, which stand as the most systematic and thorough examination of axonal projections related to any single major part of the brain in mammals (see Dong et al., 2001; Dong and Swanson, 2006). Hong-Wei went on from USC to the Allen Institute for Brain Science, where he created their mouse brain reference atlas (Dong, 2007) modeled on our rat Brain Maps (Swanson, 2004), after which he was recruited by Arthur Toga to UCLA and then USC, to develop and head up a mouse connectome project. He is now a professor in the Department of Neurobiology at UCLA.

My last doctoral student, Lee Cenquizca, started the same year Hong-Wei arrived. We decided the time was ripe to reexamine the projections of hippocampal field CA1 with the PHAL method, and he covered all dorsoventral (septotemporal) levels with injections. The results showed that field CA1 has much more extensive projections to the rest of the cerebral cortex than previously thought and that different dorsoventral levels generate projections to different sets of cortical areas (Cenquizca and Swanson, 2007). The results also showed that only the ventral pole of field CA1 projects to the hypothalamus, innervating nuclei involved in controlling motivated behavior, and to midline thalamic nuclei (Cenquizca and Swanson, 2006). Although admitted to medical school, and having his choice of postdocs, Lee decided the most worthwhile thing he could do next was give back to the community where he grew up and is now a professor in the life sciences at Los Angeles City College.

We began a systematic attack on the last remaining enigma of the hypothalamus, the lateral zone, which lasted from around 1992 until funding ran out in 2015. The greatest impetus during this period was the recognition in the lateral hypothalamic area of two distinctive neuron groups with very different projections—the parasubthalamic nucleus (Goto and Swanson, 2004) and subfornical region (Goto et al., 2005)—and this led us to a new parceling scheme with about two dozen parts (Swanson et al., 2005) and a new guide for connectivity analyses. The person who took up this new strategy was Joel Hahn, who had just finished his doctoral work on hypothalamic circuitry related to ovulation with Clive Coen at King’s College London.

Joel meticulously analyzed and superbly illustrated the inputs and outputs of five parts of the lateral hypothalamic area middle group and he found, with coinjections of PHAL/cholera toxin B, that they have the most complex set of connections of any known part of the nervous system (Hahn and Swanson, 2010, 2012, 2015). Although we did not quite finish analyzing all parts of the lateral hypothalamic zone (grant reviewers said that despite excellent productivity and important technical innovations, we were “just completing a dataset” without functional analysis, a point I return to in the Epilogue), clearly it is a highly differentiated part of the brain, with roughly the same number of parts as the thalamus, although not as clearly distinguishable. The lateral hypothalamic zone is a rich continent waiting to be explored thoroughly, as the thalamus was a century earlier.

The Birth of Neuroinformatics

Since my thesis work on ingestive behavior hot spots, the research just outlined had been guided by Grossman’s hypothesis about the existence of “motivation-specific circuits” (Grossman, 1960), which I am sure was heavily influenced by Eliot Stellar’s brilliant review, The Physiology of Motivation (Stellar, 1954). So, as the connectional data accumulated, new insights into subsystem organization began to emerge, first with my friend Gordon Mogenson in a paper called “Neural Mechanisms for the Functional Coupling of Autonomic, Endocrine and Somatomotor Responses in Adaptive Behavior” (Swanson and Mogenson, 1981); then in “The Neural Basis of Motivated Behavior” (Swanson, 1989) and “Cerebral Hemisphere Regulation of Motivated Behavior” (Swanson, 2000a); and finally, in Brain Architecture: Understanding the Basic Plan (Swanson, 2003). But the amount of relevant neuroscience data was accumulating at an unmanageable rate.

The Institute of Medicine (National Academy of Medicine since 2015) recognized the information explosion obstacle and charged a Committee on a National Neural Circuitry Database, which met during 1989–1990 and was chaired by Joseph C. Martin (then dean of the UCSF Medical School), to recommend solutions. I was fortunate to serve on the committee, whose final vision could be rephrased in today’s jargon as “create Google Earth for the brain” and whose work was summarized in a prescient book, Mapping the Brain and Its Functions: Integrating Enabling Technologies into Neuroscience Research (Pechura and Martin, 1991). Its publication could be said to mark the birth of neuroinformatics, which was nurtured by an ambitious, decade-long Human Brain Project: Neuroinformatics (HBP) that began in 1995, was sponsored by 16 federal organizations, and was coordinated by the NIMH (Huerta et al., 1993, 2006).

USC was awarded a first- (and second-) round HBP program project grant under the leadership of Michael Arbib, whose doctoral advisor in mathematics at MIT was Norbert Wiener, the brilliant founder of cybernetics. In hindsight, the best outcome of this funding was the working collaborations it promoted between faculty and students in computer science and neuroscience. I began to learn about database technology and my computer science colleagues began to learn about experimental methodology in the life sciences—and we all struggled to figure out how to merge the two in useful ways for both communities (Dashti et al., 1997; Swanson, 2001), a struggle that continues at an excruciatingly slow pace. The bioinformatics that earlier grew out of molecular biology had two great advantages: a powerful and simple conceptual framework, the double-helix model of DNA (Watson and Crick, 1953), and sequences of linear information (encoded as nucleic acids or amino acids) for databases. In contrast, neuroinformatics had the most complex three-dimensional object known to science, the brain, and no overarching conceptual framework at the systems level.

Gully Burns was the first postdoctoral fellow to join our HBP efforts, in 1997. He was just finishing his doctorate of philosophy at Oxford, and for it had collaborated with Malcolm Young at the University of Newcastle upon Tyne on a project to analyze, with multidimensional scaling and cluster analysis methodologies, rat brain connectivity data they had collated from the literature. On the basis of this experience, one important reason he was drawn to our group was the complete, internally consistent, and hierarchically organized nomenclature I had developed for the digital rat brain atlas described earlier (Swanson, 1992). Basically, his goal was to develop a hybrid textual-visual database system, using the nomenclature table for labeling data tables and the digital atlas for displaying spatially indexed information in a stack of spatially registered vector graphics layers (Shahabi et al., 1999; Dashti et al., 2001; Burns et al., 2006).

In the middle of the HBP era, a Romanian student, Mihail Bota, finished his doctorate with Arbib and joined our group as a postdoctoral fellow to develop a comprehensive Brain Architecture Knowledge Management System (BAMS). The first outcome was a Perspective article for Nature Neuroscience in which Mihai, Hong-Wei, and I accomplished two things. First, we laid out the basic problems associated with establishing the fundamental structural architecture of brain circuitry as a prerequisite for explaining behavior mechanistically. And, second, we introduced version 1.0 of BAMS (Bota et al., 2003), which went through a series of enhancements (see Bota et al., 2014). One of the basic problems with building federated database tables appropriate for inference engines was a total lack of nomenclature standardization, something foreign to more advanced fields like chemistry and electrical engineering.

During HBP meetings in San Diego, Arthur Toga (UCLA), Douglas Bowden (University of Washington), Steve Koslow (NIMH), and I informally discussed the problem of nomenclature chaos at length, and we agreed its solution was fundamental to progress in neuroinformatics. Bowden decided to evaluate and systematize terms in current use, and eventually implemented NeuroNames (Bowden and Dubach, 2003). Building on the nomenclature tables in Brain Maps (Swanson, 1992), I decided to take a comprehensive historical approach instead. During the course of this work, we proposed a solution to the neuron classification problem (Bota and Swanson, 2007a) and organized the first (and unfortunately only) International Neuroinformatics Coordinating Facility (INCF) Workshop on Neuroanatomical Nomenclature and Taxonomy, in Stockholm (Bota and Swanson, 2008). Finally, nearly 20 years later, the project culminated in the publication of a massive, 1,054-page book, Neuroanatomical Terminology: A Lexicon of Classical Origins and Historical Foundations (Swanson, 2015), and a supplement on the cerebral cortex (Swanson and Hof, 2019), that together laid out a defined and internally consistent vocabulary for all parts of the nervous system in humans and other mammals.

Connectomes

Shortly after Francis Crick died on July 28, 2004, the Salk Institute held a memorial service with Jim Watson as a featured speaker. At the reception afterward, I was surprised when Watson approached me with the anecdote that when Crick came to the Salk and switched his interests to neuroscience, the first thing he told Watson was that a physical wiring diagram was needed, analogous to the double-helix model. Then I was even more surprised when he said he hoped I would work with him and others at Cold Spring Harbor Laboratory to accomplish such a goal. This led to a joint proposal that Partha Mitra (whom I’d met at a McKnight Foundation Meeting), John Doyle (Caltech), Hans Breiter (Harvard), and I made to the Keck Foundation in Los Angeles for a pilot Brain Architecture project, which was approved in 2006 for three years and centered at Cold Spring Harbor. At the end of those three years, a position paper advocating a coordinated effort to determine brainwide connectivity in model organisms was written by Partha with input from 36 other committed researchers, including myself, John Doyle, Hans Breiter, and Jim Watson (Bohland et al., 2009).

Coinciding with these developments, Olaf Sporns, Giulio Tononi, and Rolf Kötter made a conceptual breakthrough when they gave the name “human connectome” to a comprehensive structural description (database) of the network of elements and connections forming the human brain, analogous in principle but not in practice to the human genome, which had been inspired by Watson and Crick’s double-helix model (Sporns et al., 2005). This stimulated us to put the rat connectional data entered in BAMS into a connection matrix, with about 10% of all possible connections accounted for—mostly from data generated in our own lab (Bota and Swanson, 2007b)—and to begin thinking about a more systematic approach to connectomic approaches in rat and mouse (Bota et al., 2012).

The stimulus for a mouse brain connectome came from Hong-Wei Dong after coming from UCLA to one of our lab meetings in August 2008. With youthful enthusiasm and optimism, he told me he thought he could do a complete mouse connectome in two years quite cheaply—using the double-coinjection method Rick Thompson was developing, and eventually published (Thompson and Swanson, 2010)—if only he had the right microscope. Three months later, I was in St. Louis at a meeting organized by Marc Raichle. At dinner with Marc and Olaf Sporns, I mentioned the possibility of a mouse connectome project. Marc was particularly enthusiastic and helpful, especially with Tom Insel, director of the NIMH, who was promoting large-scale projects for neuroscience (Insel et al., 2004). So, in the end, Hong-Wei got his microscope through a supplement to one of Toga’s large grants in 2009, and then got his own NIMH funding in 2012. The two-year prediction is long forgotten, although excellent progress has been made (by the Allen Institute for Brain Sciences as well), but nevertheless, a great deal remains to be done to achieve a complete and systematic mouse brain connectome using the latest technology.

My last graduate student arrived in 2011. Ramsay Brown had taken my Brain Architecture course as an undergraduate, and he was inspired by the idea of creating a “Google map for the brain.” He was an enthusiastic, outgoing, fast-thinking computer nerd. Building on a foundational model of nervous system structural connectivity that Bota and I had published the year before (Swanson and Bota, 2010), Ramsay began by creating a formal modeling language, in reality, an internally consistent notation scheme for the systematic description, unambiguous communication, and automated digital curation (with bar codes) of neural connectivity (Brown and Swanson, 2013). He then created a prototype interactive online brain mapping application (Brown and Swanson, 2015). Impatient, he took a master’s degree, and successfully entered the world of web-based startups, echoing Dennis Brittain’s departure from the Salk lab in the late 1980s.

The Ongoing Neurome Project

In 2013, we began an in-depth discussion about how to adopt a more systematic approach to probing the rat connectome, starting at the rostral end with the cerebral cortex and then, if feasible, working our way caudally through the classic major subdivisions (Swanson, 2000b). Unbeknownst to me, Bota began collating the experimental pathway tracing literature on rat cerebral cortical association connections and about a year (and nearly 4,000 hours of work) later he had assembled data on the existence of 1,923 macroconnections between the 73 cortical regions in the analysis. There are 5,256 possible connections between 73 regions, and he found data for more than 80% of all possible connections. The resulting directed and weighted connection matrix for rat cortical association connections was foundational. First, it suggested that this approach was feasible and that perhaps the greater part of the rat connectome was already in the literature, based on research published since the neuroanatomy revolution of the 1970s (Swanson, 1999). And, second, it prompted us to invite Olaf Sporns to join the project as the network analysis expert. Mihai had earlier gotten Olaf involved in a neuroinformatics project to analyze the relationship between molecular expression patterns and neuron populations (Bota et al., 2012). Olaf readily agreed to the new proposal.

Our first paper, on the organization of the cerebral cortical association network, appeared in 2015 (Bota et al., 2015). In it, we suggested that to explain behavior in mechanistic terms it would be necessary not just to understand the basic wiring diagram of the brain but also to understand the basic organizing principles of the nervous system as a whole—how the brain communicates with and directs the rest of the body—thus extending the concept of a connectome to that of a neurome. Unfortunately, this paper coincided with the end of our NIH grant support for neuroinformatics (as mentioned earlier, our NIH support for experimental research also ran out that year), and Mihai, who had been an exceptionally hardworking and valuable colleague, left for positions with Maryann Martone’s neuroinformatics group at UCSD, and then with Pavel Osten and Partha Mitra at Cold Spring Harbor.

At that point, Joel Hahn joined the effort and together with Olaf, we decided to go for the rat neurome at the macrolevel of analysis, using the basic strategy we had developed for the cortical association network, which Jeff Lichtman and I summarized in the Annual Review of Neuroscience (Swanson and Lichtman, 2016). At the time, we thought a rat neurome project might take about 10 years for the three of us to complete, without external funding, which we have not yet received (except for three years of partial support for Joel’s salary from the Kavli Foundation, thanks to Miyoung Chun). Joel’s first major contribution was the creation of an elaborate, conditionally formatted Excel worksheet (Axiome) to record connection report metadata and port it to MATLAB for network analysis by Olaf (Swanson et al., 2016). This tool speeded up by an order of magnitude the expert collation procedure and, at the same time, increased its accuracy—making the estimate of a 10-year project realistic.

With Mihai gone, I decided to collate again the cortical association network and extend the analysis to cortical commissural connections. Our cortical association paper was the most complete to date, but it had not broken significant new ground—similar analyses had already been done on monkey, cat, and mouse by others. But cortical commissural connections had not been analyzed systematically, nor had any major subcortical nervous system subdivision. This collation identified connectional data for 94% of the 23,562 possible connections between 144 cortical regions on both sides of the brain, strengthening our hypothesis that most of the rat neurome might already be in the literature (Swanson et al., 2017). The network analysis revealed small sets of intracortical hubs, rich club members, and subsystems as well as a set of 14 unexpected “rules” associated with the distribution of commissural connections. This included the observation that there is an order of magnitude more heterotopic connections (from a particular region on one side, to a noncorresponding region on the other side) than homotopic connections (from a particular region on one side, to the corresponding region on the other side).

To date, we have published eight papers on the rat neurome, covering the intrinsic network connectivity of the bilateral cerebral cortex, cerebral nuclei, endbrain (cerebral cortex and nuclei together), thalamus, hypothalamus, interbrain (thalamus and hypothalamus together), and forebrain (endbrain and interbrain together). As a member of the National Academy of Sciences, I was fortunate to have quick access to quality publication of our findings in their Proceedings.

References to the earlier work are found in the forebrain paper (Swanson et al., 2020), which is based on 375,020 separate reports expertly collated from the experimental pathway-tracing literature about an axonal connection from one forebrain gray matter region to another gray matter region. Because there are 216,690 possible macroconnections between the 466 forebrain gray matter regions on both sides of the brain (466²-466), on average there are almost two (actually 1.7) different reports in the literature for each possible connection. This figure is complemented by the fact that evidence was found for the presence or absence of 95% of the possible 216,690 connections, thus leaving only 5% of the possible connections completely unexplored. The analysis of this rich dataset, which represents a halfway point in our neurome project, is notable for several reasons.

First, the forebrain connectome is sexually dimorphic, so separate analyses and network features are associated with the adult male and female rat. Second, in addition to being weighted and directed, all forebrain connections have a provisional sign: they are associated with excitatory/glutamatergic or inhibitory/GABA synaptic transmission, with all of the usual disclaimers, as first done for the hypothalamic connectome (Hahn et al., 2019). Third, the extremely enlightening multiresolution consensus clustering method introduced by Lucas Jeub, Olaf Sporns, and Santo Fortunato (Jeub et al., 2018), and first applied to the endbrain connectome analysis (Swanson et al., 2018), was used to create a hierarchy of forebrain structure-function subsystems based on sets of highly interconnected regions. There are 166 structure-function subsystems or modules, arranged such that there are just two at the top level and 92 at the bottom level of the hierarchy, which now acts as a powerful hypothesis-generating engine for experimental manipulation of the intra-forebrain wiring diagram.

Our experience thus far clearly shows that analysis of subconnectomes (whether in cerebral cortex, hypothalamus, or forebrain) yields fundamental insight into the intrinsic network organization associated with particular subconnectomes, and also shows that network features change when anatomical coverage of a network changes. Thus, basic design features of an entire nervous system wiring diagram cannot emerge until a neurome project is completed.

Conversely, our experience also suggests that a rather complete neurome for at least one mammal, the rat, is already in the literature at the macroscale of analysis. This is the result of almost 50 years of research with experimental pathway tracing methods by around 275 laboratories. Because generating this type of circuitry data has been the focus of our lab throughout that 50-year period, it may not be surprising that, as outlined earlier, we have generated about 26.3% of the connection reports for the forebrain analysis. Other major contributors include groups headed by Clif Saper (4.6%), Robert Vertes (3.4%), Joel Price (2.9%), and Sara Shammah-Lagnado (2.6%). It is no coincidence that three of the five groups originated in Max Cowan’s Anatomy and Neurobiology Department at Washington University in the 1970s, or that about 55% of the connection reports were published in the Journal of Comparative Neurology (1 of 53 sources), which was edited by Cowan from 1968–1980, and by Saper from 1994–2011. Finally, it is encouraging to see that the results of this truly basic research may begin to find translational research applications, exemplified by a recent network hypothesis about possible mechanisms underlying the pattern of tauopathy spread in Alzheimer’s disease (Small and Swanson, 2019).

History, Cajal, Books, and Teaching

Cowan’s Department of Anatomy and Neurobiology in the 1970s arguably had the best concentration of structural neuroscience-neuroanatomy expertise ever assembled, with major contributors including, among others, Max himself, Ted Jones, Richard and Mary Bunge, Joel Price, Tom Woolsey, David Gottlieb, Arthur Loewy, and Clif Saper. Part of the excellence was a pervasive respect for precedence and the history of science that was probably a by-product of Max, Ted, and Joel’s training at Oxford. Fortunately, the entrance to the superb Medical School Library, directed by Estelle Brodman, was just one flight of stairs down from my lab, making it easy to carry out the scholarship expected in traditional anatomical and physiological publications. But another part of the excellence was a pervasive admiration for the work of Santiago Ramón y Cajal, whose late-nineteenth-century neuron doctrine and law of functional polarity were the cornerstones of modern neuroscience at the cellular and systems levels of analysis.

In 1978, I spent the summer at the University of Bergen through the invitation of Wilhelm Harkmark and Bolek Srebro, doing a Golgi study of neurons in layer two of the hippocampal formation’s presubiculum—and I wondered whether Cajal had already described the neurons I was drawing. We were staying in the house of psychology professor Holger Ursin, who was on sabbatical at UCSD and who had a copy of Cajal’s two-volume masterpiece, the Histologie (1909–1911), on his shelves. I asked Neely if she would translate the appropriate chapter (she was a French major in college), and she did an excellent job; Cajal had briefly mentioned three different types of neuron in layer two, but none were illustrated.

Coincidentally, three years later Cowan was approached by the Consejo Superior de Investigaciones Científicas (Madrid) about overseeing an English translation of the Histologie, and I soon gave him a copy of Neely’s translation, which I had edited for scientific content and style. In 1984, Max finally received a first payment from the Consejo and gave the job of doing an initial translation to Neely. That money allowed her to buy an IBM PC, introduced only a year earlier. Four years later, Neely finished her job, but Max had moved on to the HHMI and was too busy for the project. I felt Neely and I could finish the job, but as proof of principle suggested we first translate Cajal’s short but key precursor, Nouvelles Idées sur la Structure du Système Nerveux chez l’Homme et chez les Vertebrés (1894). We discussed the plan over margaritas at dinner one night with a new Salk arrival from Yale, Charles (Chuck) Stevens, and through a contact of his at MIT Press, Fiona Stevens (no relation), we secured a contract for the translation (Swanson and Swanson, 1990). Then, in 1991, Neely and I signed a contract with Oxford University Press, arranged by Jeffrey House (who was married to Fiona Stevens), for the Histologie translation, which was published in 1995 (Swanson and Swanson, 1995). To round things out, Neely and I translated a third book of Cajal’s, his entertaining and still quite instructive Reglas y Consejos sobre Investigación Cientifica: Los tónicos de la voluntad (Advice to a Young Investigator; Swanson and Swanson, 1998). It was an honor and profound learning experience to deal so intimately with Cajal’s written work. It is also remarkable to see how his reputation as the greatest scientist in Spain’s long history, and as an artist, continues to grow (Saltz, 2018).

Considering my love of neuroscience history, it is no surprise that one of my favorite pastimes (aside from family, friends, and travel) is collecting books related in one way or another to the structure and function of the nervous system. This bibliomania really started in 1979. On our way back from the summer in Kuypers’s Rotterdam laboratory, we stopped in London, and at an eye-opening visit to Dawson’s of Pall Mall bookstore, Neely and I bought a copy of Bernhard Siegfried Albinus’s magnificent Tabulae Sceleti et Musculorum Corporis Humani of 1747. It remains a cornerstone of my collection, along with the acquisition over 40 years later of a copy of Dryander’s 1537 Anatomiae, the first book devoted to brain anatomy. Over the years, it has been a pleasure to get to know and work with many book dealers and collectors, including Jeremy Norman, Barbara Rootenberg, Malcolm Kottler, the late Michael Thompson and William Conrad Cooper, James Tait Goodrich, Bruce Fye, Ove Hagelin, Arthur Lyons, Eugene Flamm, Fritz-Dieter Söhn, and Christian Westergard, along with Daniel Lewis and Joel Klein at the Huntington Library.

I also have found teaching a rewarding way to pass along ways of thinking and knowledge to the next generation. My introduction was as an assistant in neural science courses that Max Cowan and Ted Jones gave at Washington University. But the real work began during the Salk years, when I volunteered from 1982 to 1989 to teach the neuroanatomy course required of all first-year neuroscience graduate students at UCSD. It had previously been taught by the eminent neuroscientist Robert Y. Moore, but he had moved on to Stony Brook University. I gave all of the lectures and labs, which was an invaluable learning experience. After I left for USC, my close friend Harvey Karten, another eminent neuroscientist who came to UCSD in 1986, took over. Then, when we moved to USC, I offered a similar course for the Neurobiology Graduate Program, and this UCSD-USC coursework led to the book Brain Architecture: Understanding the Basic Plan (Swanson, 2003). It was not a traditional neuroanatomy textbook detailing all of the major components of the nervous system and the connections between them. Instead, it focused on overall design principles and a novel set of four basic structure-function subsystems.

Administration

I was determined to spend an absolute minimum amount of time on administration, and a maximum on research, until I got a call in 1998 from the dean of the college at USC asking if he could come over to my office to talk. He asked if I would take over the job of dean of research for two years from molecular biologist Maria Pellegrini, who was leaving for the Keck Foundation. I said no, but within 10 minutes, he convinced me to do it half-time, focusing on the larger issues and continuing my research at the same time. The dean was Morton O. (Morty) Schapiro, who went on to great success as president of Williams College, and then Northwestern University. He was the best administrator with whom I ever worked, but at the end of the two years, I felt I was doing two full-time jobs and decided to focus on one—my real love, research.

To me, one aspect of research has been giving back to the community through professional organizations, first and foremost the Society for Neuroscience. Since that first meeting in 1971 when I was looking for a postdoc, I have attended every single meeting. One accomplishment as president (2012–2013), and later as co-chair with Magda Giordano of the 50th Anniversary Planning Group, was to help ensure that the first 50 years of the society’s history was thoroughly and objectively preserved and documented. A second enriching experience has been membership in the Cajal Club, the oldest neuroscience organization in North America, having been founded one midnight in 1947 by a group of socializing brain researchers at the annual meeting of the American Association of Anatomists (Whitlock, 2007). In typical club fashion, I was recruited late one night at a New Orleans bar in 2003 (during a Society for Neuroscience meeting) by Charles (Chuck) Ribak, Efrian Azmitia, and John Morrison, and served as president from 2004 to 2006. Highlights from that appointment included transitioning from the American Association of Anatomists meeting to the Society for Neuroscience meeting, and two successful international conferences, one at the Karolinska Institutet in 2006 to celebrate the 100th anniversary of the Nobel Prize to Cajal and Golgi (Swanson et al., 2007), and the other at the National Autonomous University of Mexico’s Institute of Neurobiology in Querétaro (Mexico), on degeneration and regeneration in the nervous system (Ribak et al., 2009). And later, as historian and archivist, I orchestrated transfer of the Club archives to the Louise M. Darling Biomedical Library at UCLA (which also holds the Society for Neuroscience archives) with the help of Chuck and Russell Johnson, Curator of the History and Special Collections for the Sciences. Finally, I had the honor of serving as secretary general (2015–2017) of the International Brain Research Organization (IBRO), where I helped launch Young IBRO, an initiative to incorporate a diverse group of younger researchers into the deliberations and decision making of the organization.

Epilogue

Looking back, I have been exceptionally lucky. I had inspirational mentors at Pomona College and Washington University, a truly outstanding succession of students and collaborators, and invaluable administrative support from David Warren and Cathleen Crayton. But most important, I have a loving and supportive family in Neely, Reid, and Reid’s partner Lee. I could not have been prouder in 2010 when I accompanied Reid—both of us in USC’s academic gowns—as he received his doctorate in computer science. And I was exposed to a whole different creativity subculture through Neely’s Los Angeles career in television production and as a lecturer in USC’s School of Cinematic Arts. What fun and enlightenment to interact with directors like my very good friend Arvin Brown, producers like another friend, Alice West, writers like David E. Kelley, and actors like Mariette Hartley, Peter MacNicol, Kate Burton, Rita Moreno, Loretta Divine, and Michael York. Imagine my surprise to learn that Sharon Stone, who was introduced to me by Neely while she was working on set, had read Brain Architecture as part of her desire to learn as much about the brain as she could following her cerebral aneurysm surgery. How fulfilling to learn they are as interested in learning about the brain as I am in the whole creative process of television.

And, of course, timing is always a critical factor. I was in on the beginning of the 1970s experimental neuroanatomy revolution and rode the crest of that wave thanks to NIH support until 2015, when another wave began forming—one that focused on systems neuroscience, theoretical network analysis, and the relationship between neural circuits and behavior. But with waves there are troughs, and structural biology (including neuroanatomy) has always had its ups and downs. This, despite the basic principle that structure and function are equally important, two sides of the same coin, which has been driven home to me from teaching the systems component of introductory biology for almost 20 years at USC.

For me, the turn of the twenty-first century was a trough when elite journals would publish structural analyses only if they were a component of, and supported, functional analyses. The same generally held true for the funding of NIH grant applications. Of the approximately 5,000 RO1 grants related to neuroscience, only a handful were focused on in-depth analyses of structural problems, a major shift from 20 years earlier. History proves that this is a short-sighted, counterproductive, and unbalanced approach to the life sciences, especially because a new generation of powerful structural neuroscience tools has been developed recently. Accurate and reliable structural analyses of lasting value are time consuming, whereas small, focused studies add precious little when appended as afterthoughts to functional analyses. The best long-term outcome for neuroscience, and for the life sciences generally, depends on two basic ingredients. One is a healthy balance between structural and functional analyses, and the other is a healthy balance between experimental and theoretical approaches, like that found in more established fields, such as physics.

References

Alvarez-Bolado G, Rosenfeld MG, Swanson LW. A model of forebrain regionalization based on spatiotemporal patterns of POU-III homeobox gene expression, birthdates, and morphological features. J Comp Neurol 355: 237–295, 1995.

Alvarez-Bolado G, Swanson LW. Developmental Brain Maps: Structure of the Embryonic Rat Brain. Amsterdam: Elsevier, 1996. Retrieved March 31, 2020, at http://larrywswanson.com/

Amara SG, Arriza JL, Leff SE, Swanson LW, Evans RM, Rosenfeld MG. Expression in brain of a messenger RNA encoding a novel neuropeptide homologous to calcitonin gene-related peptide. Science 229: 1094–1097, 1985.

Barinaga M. Californians thinking bigger in neuroscience for the 1990s. Nature 331: 554, 1988.

Bloom F, Battenberg ELF, Rivier J, Vale W. Corticotropin releasing factor (CRF): immunoreactive neurones and fibers in the rat hypothalamus. Reg Peptides 4: 43–48, 1982.

Bohland JW, Wu C, Barbas H, Bokil H, Bota M, Breiter HC, Cline HT, Doyle JC, Freed PJ, Greenspan RJ, Haber SN, Hawrylycz M, Herrera DG, Hiltetag CC, Huang ZJ, Jones A, Jones EG, Karten HJ, Kleinfeld D, Kötter R, Lester HA, Lin JM, Mensh BD, Mikula S, Panksepp J, Price JL, Safdieh J, Saper CB, Schiff ND, Schmahmann JD, Stillman BW, Svoboda K, Swanson LW, Toga AW, Van Essen DC, Watson JD, Mitra P. A proposal for a coordinated effort for the determination of brainwide neuroanatomical connectivity in model organisms at a mesoscopic scale. PLoS Comp Biol 5: e1000334, 2009.

Bota M, Dong H-W, Swanson LW. From gene networks to brain networks. Nature Neurosci 6: 795–799, 2003.

Bota M, Dong H-W, Swanson LW. Combining collation and annotation efforts toward completion of the rat and mouse connectomes in BAMS. Front Neuroinform 6: 1–10, 2012.

Bota M, Sporns O, Swanson LW. Neuroinformatics analysis of molecular expression patterns and neuron populations in gray matter regions: the rat BST as a rich exemplar. Brain Res Rev 1450: 174–193, 2012.

Bota M, Sporns O, Swanson LW. Architecture of the cerebral cortical association connectome underlying cognition. Proc Natl Acad Sciences USA 112: E2093–E2101, 2015.

Bota M, Swanson LW. The neuron classification problem. Brain Res Rev 56: 79–88, 2007a.

Bota M, Swanson LW. Online workbenches for neural network connections. J Comp Neurol 500: 807–814, 2007b.

Bota M, Swanson LW. 1st INCF workshop on neuroanatomical nomenclature and taxonomy. Nature Precedings, 2008. Retrieved March 31, 2020, at http://dx.doi.org/10.1038/npre.2008.1780.1

Bota M, Talpalaru S, Hintiryan H, Dong H-W, Swanson LW. BAMS2 Workspace: a comprehensive and versatile neuroinformatic platform for collating and processing neuroanatomical connections. J Comp Neurol 522: 3160–3176, 2014.

Bowden DM, Dubach MF. NeuroNames 2002. Neuroinformatics 1: 43–59, 2003.

Brittain DA. The efferent connections of the infralimbic area in the rat. Ph.D. Thesis, University of California, San Diego, 1988.

Brown RA, Swanson LW. Neural Systems Language: a formal modeling language for the systematic description, unambiguous communication, and automated digital curation of neural connectivity. J Comp Neurol 521: 2889–2906, 2013.

Brown RA, Swanson LW. Golgi: interactive online brain mapping. Front Neuroinform 9(26): 1–16, 2015.

Burns GAPC, Cheng W-C, Thompson RH, Swanson LW. The NeuARt II system: a viewing tool for neuroanatomical data based on published neuroanatomical atlases. BMC Bioinformatics 7: 531 (19 pp.), 2006.

Cajal SRy. Nouvelles Idées sur la Structure du Système Nerveux chez l’Homme et Chez les Vertebrés, translated from Spanish by L Azoulay and reviewed and augmented by the author. Paris: Reinwald & Cie, 1894.

Cajal SRy. Histologie du Système Nerveux de l’Homme et des Vertébrés, translated from Spanish by L Azoulay, 2 volumes. Paris: Maloine, 1909–1911. The quote is from the English translation: see Swanson N, Swanson LW (1995).

Canteras NS, Chiavegatto S, Ribeiro do Valle LE, Swanson LW. Severe reduction of defensive behavior to a predator by discrete hypothalamic chemical lesions. Brain Res Bull 44: 297–305, 1997.

Canteras NS, Simerly RB, Swanson LW. The connections of the posterior nucleus of the amygdala. J Comp Neurol 324: 143–179, 1992.

Canteras NS, Swanson LW. Projections of the ventral subiculum to the amygdala, septum, and hypothalamus: a PHAL anterograde tract-tracing study in the rat. J Comp Neurol 324: 180–194, 1992.

Cenquizca LA, Swanson LW. An analysis of direct hippocampal cortical field CA1 axonal projections to diencephalon in the rat. J Comp Neurol 497: 101–114, 2006.

Cenquizca LA, Swanson LW. Spatial organization of direct hippocampal field CA1 axonal projections to the rest of the cerebral cortex. Brain Res Rev 56: 1–26, 2007.

Cowan WM, Gottlieb DI, Hendrickson AE, Price JL, Woolsey TA. The autoradiographic demonstration of axonal connections in the central nervous system. Brain Res 37: 21–51.

Dahlström A, Fuxe K. Evidence for the existence of monoamine-containing neurons in the central nervous system. I. Demonstration of monoamines in the cell bodies of brain stem neurons. Acta Physiol Scand Suppl 232: 1–55, 1964.

Dashti A, Burns GAPC, Ghandeharizadeh S, Jia S, Shahabi C, Simmons M., Stone J, Swanson LW. The “neuroanatomical rat brain viewer” (“NeuARt”): a system for registering data against brain atlases. In Arbib MA, Grethe JG (Eds.). Computing the Brain: A Guide to Neuroinformatics. San Diego: Academic Press, 2001 (pp. 189–202).

Dashti AE, Ghandeharizadeh S, Stone J, Swanson LW, Thompson RH. Database challenges and solutions in neuroscientific applications. Neuroimage 5: 97–115, 1997.

de Lima MAX, Baldo MVC, Canteras NS. Revealing a cortical circuit responsive to predatory threats and mediating contextual fear memory. Cereb Cortex 29: 3074–3090, 2019.

Dong H-W. Allen Reference Atlas: A Digital Color Brain Atlas of the C57 Black/6J Male Mouse. Hoboken: Wiley, 2007.

Dong H-W, Petrovich GD, Swanson LW. Topography of projections from amygdala to bed nuclei of the stria terminalis. Brain Res Rev 38: 192–246, 2001.

Dong H-W, Swanson LW. Projections from bed nuclei of the stria terminalis, anteromedial area: cerebral hemisphere integration of neuroendocrine, autonomic, and behavioral aspects of energy balance. J Comp Neurol 494: 142–178, 2006.

Evans RM, Swanson L, Rosenfeld MG. Creation of transgenic animals to study development and as models for human disease. Rec Prog Horm Res 41: 317–337, 1985.

Gorski RA, Gordon JH, Shryne JE, Southam AM. Evidence for a morphological sex difference within the medial preoptic area of the rat brain. Brain Res 148: 333–346, 1978.

Gerfen CR, Sawchenko PE. An anterograde neuroanatomical tracing method that shows the detailed morphology of neurons, their axons and terminals: immunohistochemical localization of an axonally transported plant lectin, Phaseolus vulgaris leucoagglutinin (PHA-L). Brain Res 290: 219–238, 1984.

Gold RM. Hypothalamic obesity: the myth of the ventromedial nucleus. Science 182: 488–490, 1973.

Goto M, Swanson LW. Axonal projections from the parasubthalamic nucleus. J Comp Neurol 469: 581–607 2004.

Goto M, Canteras NS, Burns G, Swanson LW. Projections from the subfornical region of the lateral hypothalamic area. J Comp Neurol 493: 412–438, 2005.

Grossman, SP. Eating or drinking elicited by direct adrenergic or cholinergic stimulation of hypothalamus. Science 132: 301–302, 1960.

Haglund L, Swanson LW, Köhler C. The projection of the supramammillary nucleus to the hippocampal formation: an immunohistochemical and anterograde transport study with the lectin PHA-L in the rat. J Comp Neurol 229: 171–185, 1984.

Hahn JD, Sporns O, Watts AG, Swanson LW. Macroscale network architecture of the hypothalamus. Proc Natl Acad Sci USA 116: E8018–E8027, 2019.

Hahn JD, Swanson LW. Distinct patterns of neural input and outputs of the juxtaparaventricular and suprafornical regions of the lateral hypothalamic area in the male rat. Brain Res Rev 64: 14–103, 2010.

Hahn JD, Swanson LW. Connections of the lateral hypothalamic area juxtadorsomedial region in the male rat. J Comp Neurol 520: 1831–1890, 2012.

Hahn JD, Swanson LW. Connections of the juxtaventromedial region of the lateral hypothalamic area in the male rat. Front Syst Neurosci 9: 66 (pp. 53), 2015.

Hartman BK, Udenfriend S. Immunofluorescent localization of dopamine ß-hydroxylase in tissues. Mol Pharmacol 6: 85–92, 1970.

He X, Treacy MN, Simmons DM, Ingraham HA, Swanson LW, Rosenfeld MG. Expression of a large family of POU-domain regulatory genes in mammalian brain development. Nature 340: 35–42, 1989.

Huerta MF, Koslow SH, Leshner AI. The human brain project; an international resource. Trends Neurosci 16: 436–438, 1993.

Huerta MF, Liu Y, Glanzman DL. A view of the digital landscape for neuroscience at NIH. Neuroinformatics 4: 131–138, 2006.

Insel TR, Volkow ND, Landis SC, Li T-K, Battey JF Jr, Sieving P. Limits to growth: why neuroscience needs large-scale science. Nature Neurosci 7: 426–427, 2004.

Jeub LGS, Sporns O, Fortunato S. Multiresolution consensus clustering in networks. Sci Rep 8: 3259, 2018.

Ju G, Swanson LW. Studies on the cellular architecture of the bed nuclei of the stria terminalis in the rat: I. Cytoarchitecture. J Comp Neurol 280: 587–602, 1989.

Ju G, Swanson LW, Simerly RB. Studies on the cellular architecture of the bed nuclei of the stria terminalis in the rat: II. Chemoarchitecture. J Comp Neurol 280: 603–621, 1989.

Kelly J, Swanson LW. Additional forebrain regions projecting to the posterior pituitary, preoptic region, bed nucleus of the stria terminalis, and zona incerta. Brain Res 197: 1–9, 1980.

Kuypers HG, Maisky VA. Retrograde axonal transport of horseradish peroxidase from spinal cord to brain stem cell groups in the cat. Neurosci Lett 1: 9–14, 1975.

Leibowitz SF. Paraventricular nucleus: a primary site mediating adrenergic stimulation of feeding and drinking. Pharmacol Biochem Behav 8: 163–175, 1978.

LeVay S. A difference in hypothalamic structure between heterosexual and homosexual men. Science 253: 1034–1037, 1991.

Lind RW, Swanson LW, Ganten D. Organization of angiotensin II immunoreactive cells and fibers in the rat central nervous system: an immunohistochemical study. Neuroendocrinol 40: 2–24, 1985.

Markakis EA, Swanson LW. Spatiotemporal patterns of secretomotor neuron generation in the parvicellular neuroendocrine system. Brain Res Rev 24: 255–291, 1997.

Mogenson GJ. The Neurobiology of Behavior: An Introduction. Hillsdale NJ: Lawrence Erlbaum, 1977.

Myelnikov D. Gigantic mice—from eggs injected with growth hormone genes. AnNex: Animal Research Nexus, 2020. Retrieved on March 7, 2020, at https://animalresearchnexus.org/index.php/blogs/mouse-jokes

Nauta WJH, Haymaker W. Hypothalamic nuclei and fiber connections. In Haymaker W, Anderson E, Nauta WJH (Eds.). The Hypothalamus. Springfield: Thomas, 1969 (pp. 136–209).

Oncken, E. LV youth “birthmate” of astronaut’s son. Las Vegas Sun, 1962. Retrieved on February 3, 2020, at https://newspaperarchive.com/las-vegas-sun-feb-22-1962-p-2/

Palmiter RD, Brinster RL, Hammer RE, Trumbauer ME, Rosenfeld MG, Birnberg NC, Evans RM. Dramatic growth of mice that develop from eggs microinjected with metallothionein-growth hormone fusion genes. Nature 330: 611–615, 1982.

Pechura CM, Martin JB. Mapping the Brain and Its Functions: Integrating Enabling Technologies into Neuroscience Research. Washington, DC: National Academy Press, 1991.

Petrovich GD, Canteras NS, Swanson LW. Combinatorial amygdalar inputs to hippocampal domains and hypothalamic behavior systems. Brain Res Rev 38: 247–289, 2001.

Petrovich GD, Scicli AP, Thompson RF, Swanson LW. Associative fear conditioning of enkephalin mRNA levels in central amygdalar neurons. Behav Neurosci 114: 681–686, 2000.

Ribak CE, Aramburo C, Jones EG, Larriva Sahd JA, Swanson LW (Eds.). From Development to Degeneration and Regeneration of the Nervous System. New York: Oxford University Press, 2009.

Risold PY, Canteras NS, Swanson LW. Organization of projections from the anterior hypothalamic nucleus: a PHAL study in the rat. J Comp Neurol 348: 1–40, 1994.

Risold PY, Swanson LW. Structural evidence for functional domains in the rat hippocampus. Science 272: 1484–1486, 1996.

Risold PY, Swanson, LW. Chemoarchitecture of the rat lateral septal nucleus. Brain Res Rev 24: 91–113, 1997a.

Risold PY, Swanson LW. Connections of the rat lateral septal complex. Brain Res Rev 24: 115–195, 1997b.

Risold PY, Thompson RH, Swanson L.W. The structural organization of connections between hypothalamus and cerebral cortex. Brain Res Rev 24: 197–254, 1997.

Rosenfeld MG, Mermod J-J, Amara SG, Swanson LW, Sawchenko PE, Rivier J, Vale WW, Evans RM. Production of a novel neuropeptide encoded by the calcitonin gene via tissue-specific RNA processing. Nature 304: 129–135, 1983.

Saltz J. Santiago Ramón y Cajal, a Nobel laureate in medicine, deserves a place next to Michelangelo and Leonardo as a draftsman. New York Magazine, March 19, 2018. Retrieved on March 22, 2020, at https://www.vulture.com/2018/03/the-doctor-whose-drawings-rival-michelangelos.html

Saper CB, Loewy AD, Swanson LW, Cowan WM. Direct hypothalamo-autonomic connections. Brain Res 117: 305–312, 1976.

Sawchenko PE, Swanson LW. A method for tracing biochemically defined pathways in the central nervous system using combined fluorescence retrograde transport and immunohistochemical techniques. Brain Res 210: 31–51, 1981.

Sawchenko PE, Swanson LW, Rivier J, Vale WW. The distribution of growth-hormone-releasing factor (GRF) immunoreactivity in the central nervous system of the rat: an immunohistochemical study using antisera directed against rat hypothalamic GRF. J Comp Neurol 237: 100–115, 1985.

Sawchenko PE, Swanson LW, Vale WW. Co-expression of corticotropin-releasing factor and vasopressin immunoreactivity in parvocellular neurosecretory neurons of the adrenalectomized rat. Proc Natl Acad Sci USA 81: 1883–1887, 1984.

Shahabi C, Dashti AE, Burns G, Ghandeharizadeh S, Jiang N, Swanson LW. Visualization of spatial neuroanatomical data. In Huijsmans DP, Smeulders AWM (Eds.). Visual Information and Information Systems. Berlin: Springer, 1999 (pp. 801–808).

Sharpe, LG, Swanson, LW. Drinking induced by injections of angiotensin into forebrain and mid-brain sites of the monkey. J Physiol 239: 595–622, 1974.

Simerly RB. Wired for reproduction: organization and development of sexually dimorphic circuits in the mammalian forebrain. Annu Rev Neurosci 25: 507–536, 2002.

Simerly RB, Swanson LW. Projections of the medial preoptic nucleus: a Phaseolus vulgaris leucoagglutinin anterograde tract-tracing study in the rat. J Comp Neurol 270: 209–242, 1988.

Simerly RB, Swanson LW, Gorski RA. The distribution of monoaminergic cells and fibers in a periventricular preoptic nucleus involved in the control of gonadotropin release: immunohistochemical evidence for a dopaminergic sexual dimorphism. Brain Res 330: 55–64, 1985.

Simerly RB, Young BJ, Capozza MA, Swanson LW. Estrogen differentially regulates neuropeptide gene expression in a sexually dimorphic olfactory pathway. Proc Natl Acad Sci USA 86: 4766–4770, 1989.

Simmons, DM, Arriza JL, Swanson LW. A complete protocol for in situ hybridization of messenger RNAs in brain and other tissues with radio-labeled single-stranded RNA probes. J Histotechnol 12: 169–181, 1989.

Small SA, Swanson LW. A network explanation of Alzheimer’s regional vulnerability. Cold Spring Harb Symp Quant Biol 83: 193–200, 2019.

Sporns O, Tononi G, Kötter R. The human connectome: a structural description of the human brain. PLoS Comp Biol 1: e42, 2005.

Stellar, E. The physiology of motivation. Psychol Rev 61: 5–22, 1954.

Swanson LW. An autoradiographic study of the efferent connections of the preoptic region in the rat. J Comp Neurol 167: 227–256, 1976.

Swanson LW. Immunohistochemical evidence for a neurophysin-containing autonomic pathway arising in the paraventricular nucleus of the hypothalamus. Brain Res 128: 345–353, 1977.

Swanson LW. Neuropeptides—new vistas on synaptic transmission. Trends Neurosci 6: 294–295, 1983.

Swanson LW. The neural basis of motivated behavior. Acta Morph Neer-Scand 26: 165–176, 1989.

Swanson LW. Biochemical switching in hypothalamic circuits mediating responses to stress. Prog Brain Res 87: 181–200, 1991.

Swanson, LW. Spatiotemporal patterns of transcription factor gene expression accompanying the development and plasticity of cell phenotypes in the neuroendocrine system. Prog Brain Res 92: 97–113, 1992a.

Swanson LW. Brain Maps: Structure of the Rat Brain. Amsterdam: Elsevier, 1992b.

Swanson LW. Brain Maps: Computer Graphics Files, Professional Version 1.0. Amsterdam: Elsevier, with 4 floppy discs, [1993].

Swanson LW. Histochemical contributions to the understanding of neuronal phenotypes and information flow through neural circuits: the polytransmitter hypothesis. In Fuxe K, Hökfelt T, Olson L, Ottoson D, Dahlström A, Björklund A (Eds.). Molecular Mechanisms of Neuronal Communication. New York: Pergamon Press, 1996 (pp. 15–27).

Swanson LW. The neuroanatomy revolution of the 1970s and the hypothalamus. In: Dunnett SB (Ed.). Highlights of Twentieth Century Neuroscience. Special issue of Brain Res Bull 50: 397, 1999.

Swanson LW. Cerebral hemisphere regulation of motivated behavior. Brain Res 886: 113–164, 2000a.

Swanson LW. What is the brain? Trends Neurosci 23: 519–527, 2000b.

Swanson LW. Interactive brain maps and atlases. In Arbib MA, Grethe JG (Eds.). Computing the Brain: A Guide to Neuroinformatics. San Diego: Academic Press, 2001 (pp. 167–177).

Swanson LW. Brain Architecture: Understanding the Basic Plan. New York: Oxford University Press, 2003. Second edition in 2012.

Swanson LW. Brain Maps: Structure of the Rat Brain. A Laboratory Guide with Printed and Electronic Templates for Data, Models and Schematics, 3rd edition. Amsterdam: Elsevier, 2004.

Swanson LW. Development of the paraventricular nucleus of the hypothalamus. In Ribak CE, Arámburo C, Jones EG, Larriva-Sahd JA, Swanson LW (Eds.). From Development to Degeneration and Regeneration of the Nervous System. New York: Oxford University Press, 2009 (pp. 69–84).

Swanson LW. Neuroanatomical Terminology: A Lexicon of Classical Origins and Historical Foundations. New York: Oxford University Press, 2015.

Swanson LW, Bota M. Foundational model of nervous system structural connectivity with a schema for wiring diagrams, connectome, and basic plan architecture. Proc Natl Acad Sci USA 107: 20610–20617, 2010.

Swanson LW, Cowan WM. Autoradiographic studies of the development and connections of the septal area. In DeFrance JF (Ed.). The Septal Nuclei. New York: Plenum, 1974 (pp. 37–64).

Swanson LW, Cowan WM. Hippocampo-hypothalamic connections: origin in subicular cortex not Ammon’s horn. Science 189: 303–304, 1975.

Swanson LW, Cowan WM. The efferent connections of the suprachiasmatic nucleus of the hypothalamus. J Comp Neurol 160: 1–12, 1975.

Swanson LW, Grant G, Grillner S, Hökfelt T, Jones EG, Morrison J (Eds). A Century of Neuroscience Discovery: Reflecting on the Nobel Prize to Golgi and Cajal in 1906. Special issue of Brain Res Rev 55: 191–498, 2007.

Swanson LW, Hahn JD, Jeub LGS, Fortunato S, Sporns O. Subsystem organization of axonal connections within and between the right and left cerebral cortex and cerebral nuclei (endbrain). Proc Natl Acad Sci USA 115: E6910–E6919, 2018.

Swanson LW, Hah J.D, Sporns, O. Structure-function subsystem model of female and male forebrain networks integrating cognition, affect, behavior, and bodily functions. Proc Natl Acad Sci USA 117 (in press).

Swanson LW, Hartman BK. The central adrenergic system. An immunofluorescence study of the location of cell bodies and their efferent connections in the rat utilizing dopamine-ß-hydroxylase as a marker. J Comp Neurol 163: 467–506, 1975.

Swanson LW, Hartman BK. Biochemical specificity in central pathways related to peripheral and intracerebral homeostatic functions. Neurosci Lett 16: 55–60, 1980.

Swanson LW, Hof PR. A model for mapping between the human and rodent cerebral cortex. J Comp Neurol 527: 2925–2927, 2019.

Swanson LW, Köhler C. Anatomical evidence for direct projections from the entorhinal area to the entire cortical mantle in the rat. J Neurosci 6: 3010–3023, 1986.

Swanson LW, Kuypers HGJM. The paraventricular nucleus of the hypothalamus: cytoarchitectonic subdivisions and organization of projections to the pituitary, dorsal vagal complex, and spinal cord as demonstrated by retrograde fluorescence double-labeling methods. J Comp Neurol 194: 555–570, 1980.

Swanson LW, Lichtman JW. From Cajal to connectome and beyond. Ann Rev Neurosci 39: 197–216, 2016.

Swanson LW, Lind RW. Neural projections subserving the initiation of a specific motivated behavior in the rat: new projections from the subfornical organ. Brain Res 379: 399–403, 1986.

Swanson LW, Marshall GR, Needleman P, Sharpe LG. Characterization of central angiotensin II receptors involved in the elicitation of drinking in the rat. Brain Res 49: 441–446, 1973.

Swanson LW, Mogenson GJ. Neural mechanisms for the functional coupling of autonomic, endocrine and somatomotor responses in adaptive behavior. Brain Res Rev 3: 1–34, 1981.

Swanson LW, Mogenson GJ, Gerfen CR, Robinson P. Evidence for a projection from the lateral preoptic area and substantia innominata to the “mesencephalic locomotor region” in the rat. Brain Res 295: 161–178, 1984.

Swanson LW, Perez VJ, Sharpe LG. Accurate and reliable intra-cerebral delivery of minute volumes of drug solutions. J Appl Physiol 33: 247–251, 1972.

Swanson LW, Sanchez-Watts G, Watts AG. Comparison of melanin-concentrating hormone and hypocretin/orexin mRNA expression patterns in a new parceling scheme of the lateral hypothalamic zone. Neurosci Lett 387: 80–84, 2005.

Swanson LW, Sawchenko PE. Hypothalamic integration: organization of the paraventricular and supraoptic nuclei. Annu Rev Neurosci 6: 269–324, 1983.

Swanson LW, Sawchenko PE, Lind RW, Rho J-H. The CRH motoneuron: differential peptide regulation in neurons with possible synaptic, paracrine, and endocrine outputs. Ann NY Acad Sci 512: 12–23, 1987.

Swanson LW, Sawchenko PE, Rivier J, Vale WW. Organization of ovine corticotropin-releasing factor immunoreactive cells and fibers in the rat brain: an immunohistochemical study. Neuroendocrinol 36: 165–186, 1983.

Swanson LW, Sawchenko PE, Wiegand SJ, Price JL. Separate neurons in the paraventricular nucleus project to the median eminence and to the medulla or spinal cord. Brain Res 198: 190–195, 1980.

Swanson, LW, Sharpe, LG. Centrally induced drinking: comparison of angiotensin II- and carbachol-sensitive sites in rats. Am J Physiol 225: 566–573, 1973.

Swanson, LW, Simmons DM. Differential steroid hormone and neural influences on peptide mRNA levels in CRH cells of the paraventricular nucleus: a hybridization histochemical study in the rat. J Comp Neurol 285: 413–435, 1989.

Swanson LW, Simmons DM, Arriza J, Hammer R, Brinster R, Rosenfeld MG, Evans RM. Novel developmental specificity in the nervous system of transgenic animals expressing growth hormone fusion genes. Nature 317: 363–366, 1985.

Swanson LW, Sporns O, Hahn, JD.Network architecture of the cerebral nuclei (basal ganglia) association and commissural connectome. Proc Natl Acad Sci USA 113: E5972–E5981, 2016.

Swanson N, Swanson LW, Translators. Santiago Ramón y Cajal: New Ideas on the Structure of the Nervous System of Man and Vertebrates. Cambridge MA: MIT Press, 1990.

Swanson N, Swanson LW, Translators. Santiago Ramón y Cajal: Histology of the Nervous System in Man and Vertebrates, 2 volumes. New York: Oxford University Press, 1995.

Swanson N, Swanson LW, Translators. Santiago Ramón y Cajal: Advice to a Young Investigator. Cambridge MA: MIT Press, 1998.

Thompson RF. An essential memory trace found. Behav Neurosci 127: 669–675, 2013.

Thompson RH, Swanson LW. Organization of inputs to the dorsomedial nucleus of the hypothalamus: a reexamination with fluorogold and PHAL in the rat. Brain Res Rev 27: 89–118, 1998.

Thompson RH, Swanson LW. Structural characterization of a hypothalamic visceromotor pattern generator network. Brain Res Rev 41: 153–202, 2003.

Thompson RH, Swanson LW. Hypothesis-driven structural connectivity analysis supports network over hierarchical model of brain architecture. Proc Natl Acad Sci USA 107: 15235–15239, 2010.

UNLV Special Collections and Archives. Guide to the William E. Ferron Family Papers. Retrieved on February 3, 2020, at https://www.library.unlv.edu/speccol/finding-aids/MS-00061.pdf

Vale W, Spiess J, Rivier C, Rivier J. Characterization of a 41-residue ovine hypothalamic peptide that stimulates secretion of corticotropin and ß-endorphin. Science 213: 1394–1397, 1981.

Wade N. The Nobel Duel: Two Scientist’s 21-Year Race to Win the World’s Most Coveted Research Prize. Garden City, NY: Anchor Press, 1981.

Watson JD, Crick FHC. Molecular structure of nucleic acids: a structure for deoxyribose nucleic acid. Nature 171: 737–738.

Watts AG, Swanson LW, Sanchez-Watts G. Efferent projections of the suprachiasmatic nucleus: I. Studies using anterograde transport of Phaseolus vulgaris leucoagglutinin in the rat. J Comp Neurol 258: 204–229, 1987.

Watts AG, Swanson LW. Efferent projections of the suprachiasmatic nucleus: II. Studies using retrograde transport of fluorescent dyes and simultaneous peptide immunohistochemistry in the rat. J Comp Neurol 258: 230–252, 1987.

Watts AG, Swanson LW. Diurnal variations in the content of preprocorticotropin-releasing hormone messenger ribonucleic acids in the hypothalamic paraventricular nucleus of rats of both sexes as measured by in situ hybridization. Endocrinol 125: 1734–1738, 1989a.

Watts AG, Swanson LW. Combination of in situ hybridization with immunohistochemistry and retrograde tract-tracing. In: Conn PM (Ed.). Methods in Neurosciences, Vol. 1: Gene Probes. San Diego: Academic Press, 1989b (pp. 127–136).

Wellcome Library. Robbins Lecturer, Pomona College, California, 2020. Retrieved on February 3, 2020, at https://wellcomelibrary.org/item/b18180723#?c=0&m=0&s=0&cv=0

Whitlock DG. The Cajal Club: its origin, originator and benefactor, Wendell J.S. Krieg. Brain Res Rev 55: 450–462, 2007.

Richard W. Tsien

BORN:

Tating, Kweichow, China

March 3, 1945

EDUCATION:

MIT, Cambridge MA, SB (Electrical Engineering) (1965)

MIT, Cambridge MA, MS (Electrical Engineering) (1966)

Oxford University, Oxford England, DPhil (Biophysics) (1970)

APPOINTMENTS:

Research student in Eaton Peabody Laboratory, Mass. Eye & Ear Infirmary (1966)

Weir Junior Research Fellow, University College, Oxford (1968–1970)

Lecturing Fellow, Balliol College, Oxford (1969–1970)

Assistant, Associate and Full Professor, Department of Physiology, Yale (1970–1974; 1974–1979; 1979–1988)

Founder and Chair, Dept. of Molecular and Cellular Physiology, Stanford (1988–1994)

George D. Smith Professor, Molecular and Cellular Physiology, Stanford (1988–2011)

Director, Silvio Conte, N.I.M.H. Center for Neuroscience Research (1991–2001)

Co-Director, Neurosciences Institute at Stanford (2000–2005)

Druckenmiller Professor of Neuroscience, N.Y.U. (2011–present)

Director, NYU Neuroscience Institute (2011–present)

Chair, Department of Neuroscience and Physiology, N.Y.U. (2012–present)

Scientific Director, Marlene and Paolo Fresco Institute for Parkinson’s and Movement Disorders (2015–present)

HONORS AND AWARDS (SELECTED)

Sir Bernard Katz Award, Biophysical Society (2020)

Ralph W. Gerard Prize, Society for Neuroscience (co-winner with R. A. Nicoll) (2014)

Annual Review Prize, Physiological Society (2014)

Julius Axelrod Prize, Society for Neuroscience (2012)

George Palade Medal (2011)

Harvey Lecture (2009)

MERIT Award, National Institutes of Mental Health (2004)

Elected as Charter Member, Biophysical Society (1999)

Elected to American Academy of Arts and Sciences (1998)

Elected to National Academy of Sciences, 1997

Elected to Academia Sinica (1996)

Walter B. Cannon Memorial Award, American Physiological Society (1996)

Elected Member, National Academy of Medicine (1994)

Magnes Prize, Hebrew University, Jerusalem (1993)

Elected Fellow, American Association for the Advancement of Science (1988)

Javits Investigator, NINDS (1986–1993)

Kenneth S. Cole Medal for Contributions to Membrane Biophysics (1985)

Established Investigator, American Heart Association (1974–1979)

Rhodes Scholar (1966–1969)

Richard Tsien has been a pioneer in the study of ion channels and synaptic transmission. He showed that cyclic AMP regulates a variety of voltage-gated ion channels and thus delineated a cardinal example of neuromodulation. He helped measure cytosolic free calcium and showed how its levels can oscillate even with membrane potential held fixed. His group defined the molecular basis of how calcium channels achieve high selectivity and rapid flux. Tsien and colleagues discovered the N-type channel, the R-type channel, and other exemplars of CaV2 calcium channels, and revealed their role in triggering fast neurotransmitter release. Work on Ca²⁺ channels led to studies of synaptic plasticity, long-term potentiation, and the cell biology of synapses, and development of innovative optical approaches. His lab has unraveled mechanisms of homeostatic synaptic plasticity, excitation-transcription coupling, and excitation-alternative splice coupling.

Richard W. Tsien

A Memorable 50-Year-Old Conversation

A rose garden in the Oxford Parks was an unlikely place for a conversation about the radial spread of depolarization in muscle fibers, but there we were more than five decades ago, Professor Alan L. Hodgkin, Nobel laureate, and myself, a 24-year-old graduate student, during a tea break of the Physiological Society. Although his lab was in Cambridge, he knew the garden, having grown up nearby (Hodgkin, 1976). Alan Hodgkin had donated 40 minutes of his precious time to bring me up to speed on his unpublished work with Adrian and Chandler on the cable theory of the spread of excitation in muscle (Adrian et al., 1969), for citation in a book I was co-authoring with my mentors (Jack et al., 1973). Hodgkin had produced an elegant derivation with lots of radial Bessel functions. We touched upon this, but I also pitched questions about what he knew about how signals got from the transverse tubules to the sarcoplasmic reticulum where the calcium was supposed to be. Didn’t there have to be some kind of special communication between the two? And were they ever electrically connected? And how did he know they weren’t electrically connected? And how did the calcium get released to activate the contractile apparatus? And so on and so forth. Alan Hodgkin treated me very kindly but squirmed a little bit because I was asking questions for which he didn’t have ready answers. Near the end of the conversation, I asked about one of his classic papers with Paul Horowicz, on the voltage-dependence of contraction (Hodgkin and Horowicz, 1960). Hodgkin looked at me, sort of blankly, and said, “You don’t happen to have a copy of that paper along, do you?” Being a naive graduate student with little experience, I replied quizzically, “But Professor Hodgkin” (and I was polite enough to address him as “professor”), “you wrote the paper; surely you must know what’s in it.” He turned to me, and with a slight trace of a smile answered “you know, the reason we write these papers is so that we don’t need to keep them in memory.”

Because my lab currently works on molecular mechanisms of memory (Cohen et al., 2018), I am fascinated by both everyday and special memories, how they are formed, recapitulated in fragments in dreams, and somehow maintained throughout a lifetime. Recalling Hodgkin’s wry remark on that day, my own cheekiness, and the curiosity we shared in questions that would take a half-century to answer (Polster et al., 2015), I reflect on memory, history, scientific enquiry, and the importance of culture. As I write, it’s Thanksgiving Day 2019, this manuscript is due in just days, and I’m taking a train to Washington to see my children and grandkids. My wife Julia and I have just been in a Penn Station deli called Zaro’s, started in 1927 by Joseph Zarubchik, a Polish émigré. The book I’ve been reading is an ambitious account of U.S. history, These Truths (Lepore, 2019). Washington is abuzz with talk of President Trump’s impeachment, Hong Kong is in turmoil, and the U.S.–China relationship is as complicated as ever. What a time to recall a chat in an Oxford garden a half-century ago.

In a personal history of neuroscience, there’s a golden opportunity to transmit lessons learned from one’s predecessors. Here are further observations of Alan Hodgkin’s particular approach to science I’d like to pass on.

Keep your eyes on the big question that interests you. Hodgkin’s work with Horowicz, leading to the discovery of chloride conductance in skeletal muscle, was found gold, but was intended merely as prelude to the ability to switch the muscle membrane potential rapidly to see how contraction was evoked.

Do your own work first before taking a full scholarly dive into what others have done. In studying muscle excitability, Hodgkin wanted to learn about the efforts of a competing group at the University of Poitiers only after he’d already formed his own opinion about the common question.

Don’t be overly worried if your competition has a better method; focus on what you find with your own. The Poitiers group had a better way of controlling muscle sodium current, a sucrose gap approach that did away with microelectrodes (Rougier et al., 1968), but Hodgkin and colleagues were unfazed—they knew their strengths (Adrian et al., 1970b).

Treat your adversaries with courtesy but firmness. Hodgkin’s courtesy to Ichiji Tasaki and his challenge to the sodium theory was a case in point (Hodgkin, 1976); in fact, he directed considerable manpower in his group to scotching Tasaki’s challenge (Baker et al., 1964; Chandler et al., 1965).

Control the writing of the paper. Hodgkin’s colleagues Richard Adrian, Knox Chandler, Leroy Costantin, and Lee Peachey joked about not being allowed to produce drafts because Alan wanted that job (this isn’t so good for mentoring, but it’s one way to assert one’s authority about the final product).

Fit tasks into suitable time vessels if you can. According to his cardiac colleague, Silvio Weidmann, Hodgkin wrote down a full theoretical appendix for Weidmann’s paper (Weidmann, 1966) on a Cambridge–London train ride. Perhaps he thrived on the pressure.

Adhere to your own standards of conduct. I asked Hodgkin about Lawrence Bragg’s kind introduction to Watson’s The Double Helix despite Watson’s portrayal of Rosalind Franklin and the questionable way she was treated (Watson, 1968), and with pursed lips he replied, “that just shows you what a gent Bragg is.”

British physiology was in full flight in the late 1960s, as Hodgkin, Andrew Huxley, and Bernard Katz branched out to study the consequences of the membrane excitability that they had so beautifully clarified (Hodgkin et al., 1952). Clarification of muscle contraction and neurotransmitter release would follow. The setting and the topics all relate in scientific and sociological ways to my own personal tale, involving ion channels, calcium signaling, neuromodulation, synaptic vesicles and excitation-response coupling.

Immigrant Origins

I come from a Chinese immigrant family. I was born in China. I came to the United States when I was two years old. I went to school in the New York City public school system. I spent two years at a private country day school on almost total scholarship. My brothers and I came from a family that was struggling. My father was an engineer, but he could not get security clearance during the Red Scare. I was raised in the crucible of a full-blown New York immigrant experience. We were living in Queens. (quoted in Haseltine, 2019) My earliest memory is of children walking along a sidewalk on the far side of the road on Halloween. I am not part of their group, nor do I recall the custom of trick-or-treating, but I am buoyed by their happiness. To this day, autumn is my favorite season and my music of choice is autumnal. It’s dusk, there’s little traffic, and scarce detail about costumes or sounds, but for sure, the kids are walking in line from right to left. Dreams can be like this—definite spatial relationships. When bears fly, there’s a clear sense of place, of spatial coordinates, of specific terrain. Perhaps this fits in with theories about how the hippocampus is involved in encoding space and time and pattern, all wrapped up together, and recapitulates them in sleep (Buzsáki, 2011). If my brain is doing this via spike sequences, I will never have primary knowledge; I am simply enjoying the unfolding progression.

I am the eldest of three boys. An early memory with more specific emotional content concerns my middle brother Louis in early 1950—our younger sib, Roger Tsien had yet to come along. I had placed a bicycle with training wheels, a rare special present, near his cot in our crowded apartment in Flushing, New York. Louis fell out of bed, cut his face on the bent metal rod that mounted a training wheel, and had to be rushed to the emergency room for stitches. Although I was supposed to safeguard my younger brother’s welfare, I had failed in this responsibility—much worse than being hurt myself. In another family episode, I picked up loose change that had fallen under the couch cushions and stored it in a glass bookcase nearby, without a plan for what to do with the coins. When my furious parents spanked me, I accepted the punishment, but asked if they would report my wrongdoing to my mother’s older brother, Yao-Tze Li (Uncle Y. T. was probably only 40 or so, but was the acknowledged leader of our extended family; he had introduced my parents to each other among other good deeds). In hindsight, this memory shows a tendency toward hoarding and awareness of social hierarchy, topics of neuroscientific interest.

Bayside, Queens, a (Non-) Melting Pot

In the 1950s, our family lived in a working-class neighborhood in Bayside, Queens, in a small brick house at 58-43 204th Street, 10 feet away from our neighbor’s house, with a narrow driveway in between. Being packed in together with so many other houses meant that we knew a lot of people in the neighborhood fairly closely. Our next-door neighbors were friendly Italians (the Rovellos) and their bungalow exuded tomato sauce with cheese. I hadn’t known what a pizza was and had never had a latke, a Jewish potato pancake, until someone kindly invited me to their house—boy, those latkes were good, straight out of bubbling fat. We were the only Chinese family within a two-mile radius (the Miaos lived in the next town, and were in touch with us). Perhaps in reaction, our parents worked hard to preserve our cultural identity, against the odds. We boys got called all sorts of interesting names, but so did everybody else. I knew all the ethnic insults for Italian, Jews, and Irish, although the Irish were a little bit higher in the totem pole. In this neighborhood, a kid could see the successive waves of U.S. immigration, like layers in sedimentary rock, and realize that you were pretty far down the hierarchy. How to fit in? Knowing about baseball gave a sense of belonging and made it harder for people to look down on you. This happened to be a golden age of baseball in New York, and we all kept track of Willie Mays, Mickey Mantle, and Duke Snyder, the center fielders of the Giants, Yankees, and Dodgers, each a future all-star. I rooted for the Yankees, based in the Bronx, because hardly anyone else in our Queens neighborhood did. Bayside was actually a wonderful place to grow up.

A Quiz Kid of Sorts

Mr. Scher was the homeroom teacher in P.S. (Public School) 162 in a class different than mine. But he would send for me to come into his class. Towering over me, he would squeeze my fat cheeks with his big hand and fire quiz questions at me—capitals of states, little math problems—and chuckle with glee when I managed to squeeze out the answers despite his grip. At the end, I got a gruff, “OK kid, go back to your class.” He was mocking me but affectionately showing me off at the same time, and I played my role, I played it straight; it didn’t occur to me until much later that he must have had a pretty good idea of what the limits of my knowledge were. This was a powerful reinforcer for gathering bits of information, caching them away in memory, just because they might come in handy someday. My dad reinforced this by telling me to be observant, only his examples were trivial: how many telephone poles did you count between X and Y?

Fired from First Job

Eighty-seven and a half cents per hour. That was the pay offered to me by the proprietor of a luncheonette, Ben Cantor, working with his wife Rho. I knew that the wage was exactly seven-eighths of a dollar—that was satisfying—and I didn’t bargain. Ben apologized that the pay might be better but rationalized it by saying that he was going to teach me many things, including “how to ride in the saddle for a long time” as if he were a master cowboy. That went over my prepubertal head though I could guess that this was something he was proud of. I remember very little about the job itself, only that after a short time Ben fired me because, as he claimed, I was unable to make small talk with the customers. In this regard I can only agree that I was much inferior to Silvio Crespo, a tall, handsome, full-blooded Italian version of a soda jerk; I was short and chubby and wore thick glasses. Beyond being fired from my first job, the most notable part of the story was how I ever got the job in the first place. It was through my mother, Yi-Ying who had sat patiently in Ben’s luncheonette to shyly ask him for a job for her son, who needed to know the value of money. Ben told me this story and confided that he was so impressed by my mother’s dignity that he couldn’t resist the chance to try out her son. Looking back on this and seeing pictures of my mother at the time, no older than my eldest daughter today, I can readily believe that she could make a case through her sincerity and quiet confidence. On some other occasion, with more time before a deadline, I would relish the chance to relay her life history, an amazing story on its own.

Stage Fright and Failure to Improvise

Scientists are trained to improvise and act calm, no matter the circumstance. Bertil Hille once had his slides dropped out of the carousel onto the floor just before a symposium talk organized by Michael Bennett. Bertil calmly put them back into the carousel in random order, correct side up, and proceeded to give his talk anyway. It wasn’t always that way for me. I played the clarinet in band and showed Mr. John Cahill, our talented music teacher, the music for “After You’ve Gone.” He got me onstage, began performing his piano accompaniment, and merrily announced without warning that I would now demonstrate the art of improvisation. To be fair, the music had a written out “improvised” part. But with no warning or instruction just to play that part, or even just the main melody, as if improvising, I froze in front of the entire assembly—not a note—while he kept playing enthusiastically. Oddly enough, no one razzed me about this embarrassment.

Boy Scouts, Parenting, and an Early Shot at Public Speaking

Joining the Boy Scouts was one way of belonging. Although my dad was too busy to participate, we had lots of surrogate parents, including the immigrant dad of other Boy Scouts. I remember Bill Vokurka’s father, the assistant scoutmaster, using his huge hands to help me with tightly rolling up my sleeping bag. The scoutmaster, Ben Mandel, gave us little sermons about Boy Scout values and we listened intently without an ounce of cynicism. The Boy Scouts chose me for a special public speaking course, held on Saturdays at the New York Public Library, which was reached by taking a bus from Bayside to Flushing, and then by transferring to the IRT subway to Bryant Park. The course drained the stage fright from giving speeches, a lasting benefit. Also, travel to Manhattan awakened an interest in urban architecture. The main library building seemed monumental in size and elegant in design, and it remained a touchstone for our family. I was much more drawn to the public edifices of New York, like the Museum of Natural History, than to Chinatown, which was crowded, dirty, and noisy, and filled with a different kind of Chinese than the Mandarin I knew. Chinatown was in no way a connection with my roots.

Sunday School and Belief in God

My mom was not a Christian, but she wanted to be sure we were equipped for our new life in the United States. When a Lutheran minister came knocking on our door, she allowed him to invite me to attend Sunday School. I did so for two and a half years, enjoying Bible stories, hymns, and a general feeling of being accepted. But I dropped out when it came time to be baptized—if one didn’t truly have faith in God, what was the point? Much later I learned that my wife Julia had gone through the same experience in her youth. Because her mother was the star soprano of their Congregationalist Church in Winchester, Massachusetts, a key to their acceptance as Chinese in such a WASP-y New England town, her decision must have taken much more independence than mine.

Sputnik, Science, and Patriotism

Talk about your experiences in that particular neighborhood; did that inform your choice to pursue science? Did you have academic parents, were they encouraging of that?

My parents were comfortable with science, but they didn’t push it on us. We three boys were just naturally inclined to it. When the Russians launched Sputnik in 1957, Americans felt that they were being outclassed by their adversaries. This prompted me to feel committed to work in science or engineering, encouraged by teachers in what was then junior high school. For example, Mr. Dobbins taught shop, but he talked about what it would be like to get a doctorate in physics at Columbia. I don’t remember thinking that going into science and engineering and space competition would put us in the same realm as H. S. Tsien, the famous Chinese rocket scientist who was my dad’s first cousin. At that time, we were focused on the Soviet Union as a threat to America. Indeed, as immigrants, we were probably a little over the top with our American patriotism.

You brought up your uncle. Could you speak about what his contributions were? Was that a source of inspiration for you? (Adler, 2015)

My uncle, Tsien Hsue Shen, the Werner von Braun of China, was a student at MIT and later a faculty member at Caltech, actively involved in the early days of the Jet Propulsion Lab; he studied aerodynamics with a famous professor there named Theodore Von Karman, and we assumed, without real evidence, that he was one of Von Karman’s best students. The first cousin of my father, H. C. Tsien, Uncle H. S. was both a distant inspiration and source of difficulty for our family during the era of Joseph McCarthy. My uncle had the misfortune to be singled out by the authorities under suspicion of being a communist, which he’d continue to vigorously deny all of his life; much of this is documented in magazine articles and in a book by Iris Chang (Chang, 2008). When H. S. Tsien’s mother was ill in China, he had prepared to ship his nonclassified books back to China. This led to his house arrest at his home in Pasadena, which went on for four years. I later visited my uncle in Beijing on two different occasions, part of an interesting relationship with China and Chinese science as mentioned later. For now, I’ll continue to chronicle our own family’s experience as immigrants whose sincere attempts at blending in to American society were hindered by my uncle’s well-known case.

Scarborough School and Social Class

My hopes of helping the exploration of outer space were encouraged by passing a competitive exam for entry into the renowned Bronx High School of Science. This opportunity was dashed by a move to Westchester, out of the NYC school system. My dad chose the town of Elmsford, not weighing heavily its public school system, which was mediocre at time. But my mother, who had missed years of schooling because her parents had given her away to a childless aunt, was dedicated to our education. Spurred by my youngest brother Roger’s aversion to public elementary school (he would vomit in protest of being taken to such a boring place despite my mom’s best efforts), she found a private school, Scarborough Country Day, that was willing to admit all three of us with minimal tuition, $200 per year per boy. We were not the only scholarship kids, but we were the only non-Caucasians in the entire school—no African Americans or Latinxs, and only a smattering of Jews and Catholics.

The school had been started by wealthy WASPs in the neighborhood near the Vanderlip estate in Scarborough-on-Hudson, between Tarrytown and Ossining. Here, surrounded by kindness and liberal intentions, I felt particularly acutely the anything-but-equal social ladder of America. Being Chinese, not well-to-do, and short and chubby was to start several steps down. I recall Steven Barry Epstein, a smart and athletic Jewish classmate who came every day to Scarborough from Mount Vernon, New York, who had been delegated to phone me to invite me to a sock hop, as if he were reaching down from the next rung up to lend me a welcoming hand. Other students were also friendly. Attending Scarborough was a valuable experience socially, probably more broadening than Bronx Science would ever have been, because my brothers and I were thrown in with rich and not-so-talented students, mixed with working-class and very talented kids like the Schmidt brothers. Frank and John Schmidt were the best athletes, the best musicians, and the handsomest kids in the school. When after-school athletics finished, they kindly gave me a ride home to Elmsford on their way home to Yonkers, their working-class town. “Charlie Chan the chunky Chinaman,” a nickname repeated with affectionate glee, was meant as a sign of belonging; another classmate’s calling Steve Epstein a “Wej,” behind his back, was nasty. At the time, I readily accepted insults about my origins when they were administered in a direct and friendly way. Accustomed to the teasing, I knew my place in the world.

Mr. J. Fulton Main, the rotund Scarborough vice principal taught science, not as an experimental method or series of concepts but as a collection of facts. Glaciers pushed a terminal moraine forward and lateral moraines to their side. Repeat. Hypnotic mnemonics, never mind principles; science was fun. Mr. Main had outlasted multiple headmasters but didn’t want the pressure of the job. He had a wonderful tenor voice and sang “Comfort Ye My People . . .” from Handel’s Messiah every Christmas. At the holiday season, I embraced the uplifting ritual that Christianity provided.

Mrs. Creighton taught not only Latin but also the lives of the Romans. She awakened a lifelong love of language and the roots of words. I remember standing in a school bus and speaking with her (or perhaps it was our French teacher) about the subjunctive mode and its strategic uses.

One of the best teachers, Mr. Stuart Ryder, a wiry, bespectacled young Yale grad, taught social studies. When I pointed out that I had managed to eke out a B+ for a paper on Hegel’s philosophy by pulling an all-nighter, he acerbically noted that there was a big difference between a B+ and an A. On one occasion, he kindly took my friend Steve Epstein and me to New Haven to watch a football game at Yale Stadium. Later, Mr. Ryder made it clear that I was not to apply to Yale because that opportunity was to be saved for Steve. I didn’t take that badly because I knew how much it would mean to my friend (he actually studied at Tufts, became an expert attorney, and collected an honorary degree from Columbia at the same graduation as my oldest daughter, Sarah). But it impressed upon me that as a Chinese-American newbie to the school, I was totally outranked.

The most important teacher for my life was Mrs. Helena Jones, the only African-American person in the entire school. Her husband worked on the assembly line at a General Motors factory in nearby Tarrytown. There was no mockery of her race—she wouldn’t have tolerated it. Once she scolded me for inattention in her geometry class, saying “you’re just loafing.” But instead of some kind of punishment or detention, her remedy was to address my boredom by encouraging me to take her courses in both algebra and geometry in the same year, with the expressed purpose of getting me qualified to take senior year calculus. The challenge, and probably the special attention, totally changed my attitude to math and to school. Even though both Mrs. Jones and I would leave Scarborough before my senior year, her intervention allowed me to take senior calculus at another high school, thereby equipping me for an easy ride with college physics thereafter: educational advantage rolling forward. I am forever indebted to Helena Jones for calling me out for laziness and building an early foundation in math.

Livingston, New Jersey, Hospitality and Lack Thereof

Just as I was approaching the rewards of senior year in high school, circumstances intervened again and we moved to New Jersey to be close to my dad’s new job at RCA. He had started his own engineering consulting company, but this had failed in the recession of 1958. During the transition period before we moved the whole family to New Jersey, my dad and I drove in his VW bug from Elmsford to East Orange, New Jersey, to meet a kind guidance counselor, Mr. John Mazzone. Mazzone was a colorful Italian American, a great fan of the musical West Side Story. He drove us the rest of the way to Livingston High School, chain smoking the entire time. Attending that school had taken some doing because we had trouble buying a house in Livingston—the developer Levin-Sagner had told us that the arrival of Chinese people would bring down housing values in the neighborhood. My brother Roger wrote about this movingly in his Nobel lecture (Tsien, 2010). Our dad protested to the New Jersey governor, Robert Meyner, and so we were grudgingly allowed to buy a house, but on a runt lot where rocks from other properties had been dumped. So we three Chinese-American boys wheel-barrowed rocks around like the Puritan farmers of New England. The high school students showed us no prejudice (there was only one other Chinese student in our class and no other Asians I can remember) and adopted me even in senior year. I played clarinet in the band and mowed lawns to earn money for lessons, took calculus with a gifted math teacher, and read novels by Thomas Hardy in an excellent English class. One memorable day, I played hooky from school and trekked to Yankee stadium with a baseball player friend named Jeff Allen, who became a beloved clinician and pediatric cancer specialist at New York University (NYU).

A Choice of Colleges

When it came time to apply for colleges, I got an early admission to MIT on the strength of my SAT scores and possibly family connections, and only later received acceptance from Harvard (Yale wasn’t even a thought, possibly because of Mr. Ryder’s stern command). In contrast to high schoolers today, I didn’t apply anywhere else—the early acceptance gave me the chance to be near my academic uncles in the Boston Area and that would have beaten anything else. MIT had offered a $700 scholarship, easily besting Harvard’s later offer of $500. Deciding was delayed until the final hour, when this monetary difference, and my mom’s persuasive argument that going to MIT would really please my dad, settled the issue. In my 16-year-old’s mind, I was on the fence anyway, so why not maximize the total happiness in the world and go along with my dad’s wishes? I had consulted with Uncle Y. T. Li, but he had taken a completely neutral position in the MIT–Harvard choice, even though he and his younger brother, Shih-Ying Lee, were both MIT professors. In retrospect, my decision was pragmatic, not rebellious against family tradition for rebellion’s sake. MIT proved to be a good option for me, mostly because it gave me valuable opportunities—extracurricular ones—that I would surely have missed at Harvard. Later, my brother Louis would follow me to MIT, while Roger branched out and went to Harvard. Roger had his own perspective on family expectations (Tsien, 2010). I include these early life stories because they convey the combination of frugality, academic confidence, idealism, and practicality that ran through my family. The obstacles we encountered didn’t come close to those experienced by other immigrant groups, but they instilled an underdog perspective.

Going to College

Tsien studied electrical engineering at the Massachusetts Institute of Technology, receiving a bachelor degree in electrical engineering in 1965. A master’s degree in 1966 was based on spectroscopy of conducting organic polymers at GE research labs in Schenectady.

Joining a fraternity was a big part of the MIT experience, which began for me at 16, in 1961. Occupying a multistory house in Back Bay close to Boston University, Beta Theta Pi was not the Hollywood stereotype fraternity of the film Animal House; the hazing and drinking were mild compared with that at more traditional schools. Instead, the Beta House was a community of male scholar-athletes, who took pride in their seriousness, like NASA astronauts so admired in those days. In each of the years up to my graduation in 1965, the Betas had the highest average grade point, exceeding Dean’s list level (4.0/5.0), even better than the women’s dormitory; they also won the all-around intramural sports trophy each year. This took hard work, time management, and upperclassmen looking after and indoctrinating the younger students. I was the first Asian American to join, aided by a connection between my immigrant uncles and Professor Charles Draper, an MIT hero, whose son James “Pox” Draper helped my consideration. Sometime later, I was told that another member had wanted to blackball me—selection was based on unanimous vote—but was dissuaded by William Koch, a now surviving member of the conservative Koch brothers. Both Bill and his slightly older twin brother (the late David Koch, who later hosted me in his grand apartment in NYC with his wife Julia) were seniors and kind to me. The Beta House included plenty of conservative Southerners and Midwesterners, far more red than blue, some now lifelong friends. Thus, I had gone from housing discrimination in Livingston to joining an all-white fraternity in little more than a year. In 1961, pre–civil rights movement, my thoughts were not on lofty concepts like racial equality but on making friends and fitting in.

MIT provided great courses, including an introductory class in signal processing by Amar Gopal Bose, the founder of the audio electronics company, one of many charismatic teachers. One of my favorite classes, on history, was taught by Emmet Larkin, an Irish historian who dared his class of engineering geeks to appreciate Thucydides’ writings about the Peloponnesian Wars. Larkin was tough, giving almost everyone including me grades no better than B+, my worst grade at MIT, but he also awakened a love of history that lives to this day. Many excellent classes followed, on statistical mechanics, for example, but I particularly savored a multiterm semiconductor course organized by Paul Gray that went all the way from semiconductor physics to the workings of transistors and amplifier circuits. He later became MIT’s president, partly on the basis of this innovative teaching. I saw Gray’s vertically integrated teaching as a role model for my own attempts at bringing molecular and systems neuroscience closer together, first with Len Kaczmarek and Steve Smith at Yale, and later, in a Stanford course I taught with Steven Baccus, entitled Information and Signaling in the Nervous System.

Having a leg up in math, thanks to Mrs. Jones’ guidance in high school, I had time for extracurricular activities. As a coxswain in the freshman crew, I was given the plum opportunity of coxing the big Harvard race, but this ended badly because our boat took on water on a stormy Charles River and sank. I could have bailed with my megaphone but didn’t think of it in the panic of the moment. My crew career never recovered, but in sticking it out for three years, I learned a lot about coaching athletes, team effort, and endurance as I trained in the winter with the oarsmen I coxed for. I loved the coaching part. Midway through MIT, I tried wrestling, partly in response to ridicule about my nonathletic physique from an upperclassman in the Beta house. I managed to reach junior varsity (JV) status in the 123-pound weight class, regularly “pulling weight” by exercising in a rubber suit to sweat down from my natural 130-pound weight, and not doing so badly at wrestling for a nine-minute match. My MIT coaches had encouraged me to try JV athletics at the college level, knowing full well that I had no high school experience in the sport. This was the kind of life experience I gained at MIT that would probably be denied at an athletically more advanced institution such as Harvard. Wrestling, like crew, was a team sport that cemented my love of team efforts and strategy. Although my fraternity brothers admired my determination, and appreciated my organizational skills as scholarship chair, intramural sports chair, and rush chair (head recruiter), I lost the election for president of the Betas to my then-roommate William Roeseler.

Bill Roeseler was older, taller, stronger, and more athletic than I was (a repeated theme, I admit) and just as academically capable and public spirited. As freshmen, Bill and I motorcycled from Boston to New York in freezing weather, heard Jose Feliciano at the Bitter End in Greenwich Village, and climbed Mount Washington in winter together with other Betas. Later, we received two precious honors together—the only MIT juniors of our year to be elected to the Tau Beta Pi engineering society, and as seniors, the Compton Cup for public service, presented by Mrs. Compton, widow of a former MIT president. Bill remains a lifelong friend despite our sharp blue–red political differences. After my house president hopes were dashed, I worked under Bill in the lesser office of pledge trainer, in effect the chief mentor/taskmaster for new freshmen, the next most important leadership role. This was a chance to coach, to pass on values. Two Betas in classes after Bill’s and mine were nascent neuroscientists, the late Peter Getting (1967) and Robert Macdonald (1966, more about his critical role in a moment).

Despite the freshman crew debacle, I entered student politics and managed by narrow margins to win election as class treasurer and later senior class president. Class activities were not political—this was before a full-blown antiwar movement—but included organizing events. I put on concerts by the Canadian folk group Ian and Sylvia and saxophonist Stan Getz’s group featuring xylophonist Gary Burton, choices ahead of their time in musical taste. The proceeds allowed me to run a concert for our graduating class featuring the famous Dave Brubeck Quartet, charging seniors and their family members $1 each. This “Graduation Eve” gala for families was a first for MIT, and it gave me a chance to play the role of community organizer, behind-the-scenes impresario, and poster artist. The flexibility and personal mentoring that Dean Kenneth Wadleigh offered me in launching Graduation Eve was a special part of MIT—perhaps he saw a future dean. Once again, I had lucked out in my choice of colleges, even beyond the superb technical education I had gained.

Real-World Experience at General Electric

My dad didn’t have a very high opinion of my MIT education—the branch of electrical engineering that I had chosen was much too conceptual, not hands-on like his own mechanical engineering background at Jiaotong University and MIT. I got a chance to do more with my hands in the MIT Cooperative Master’s Program, a program with remote sites offering what were in effect research internships with a remote practical supervisor and a nominal head of committee on campus. I opted for GE research labs in Schenectady, New York, up the Hudson from New York City. I had worked for two summers at a power company, Jersey Central Power and Light, to help pay for college, but that involved routine calculations of the impedance of power lines, not research. At GE, I was given projects at the border between materials science and engineering. Students were a rare commodity, so I got lots of good mentoring from Alec Sharbaugh, Oliver Leblanc, and Charles (Chip) Huggins. In the first summer of the GE internship, I measured the critical voltage at which dielectric films broke down. Whenever things didn’t work, Alec would say in the most cheerful tone, “Well, that’s research!” As with Mr. Main at Scarborough School, it wasn’t the information content but the buoyant tone that made it all seem worthwhile.

Later, Leblanc and Huggins guided my experiments using electron paramagnetic resonance (EPR) to study the properties of organic polymers made by a chemist named John Lupinski. Huggins was smart and ambitious, and he nattily dressed in crisp white business shirts and chain smoked (smoking was allowed in the workplace back then—think Mad Men). Leblanc was quietly intelligent and more casual (plaid shirts), and like Huggins, he spoke with a North Carolina drawl. Together, they directed my study, cheered the experiments, and put together a first-authored paper for us in the Journal of Chemical Physics (Chip had wistfully talked about Nature, but Ollie talked him out of it). They were closet professors, working in a setting that rivaled Bell Labs, without the pressure of academia, going home when they wanted. For my part, I loved listening to their stories, working at the EPR machine, improving my tennis, and having the time to take up folk guitar. Schenectady was close enough to Massachusetts to allow me to drive a blond, folk-singing secretary to Woods Hole for a long day’s date, riding in the VW bug passed on from my dad. I roomed with another MIT student, Joe Waters from Mississippi, who loved country music and finger-picking “Wildwood Flower.” Unlike Julia, my beloved partner of five decades, who abhors anything with a twang, I came to love it.

In our guitar playing, Joe and I met another young scientist who seemed mortal enough—not an athlete at all, a confident nerd—despite his status as a former Rhodes scholar. This helped dispel my notion that all Rhodes scholars were stars in sports like Pete Dawkins (or later, Bill Bradley) and so I decided to apply myself. GE was critical in emboldening this by providing research experience, warm mentorship and a chance to grow socially. After applying from New Jersey, having really lived there for only one year, I emerged from that state, proceeded to the Middle Atlantic regional interviews at Johns Hopkins in Baltimore, where I wound up competing with Henry Lester, now an honored fellow neuroscientist, who had been at Harvard like so many other contestants. Four out of twelve were selected for the scholarship. I would be the only Asian in the group of 32 scholars, but one of the other Mid-Atlantic winners, representing New York state, was Richard Joseph, of Afro-Caribbean descent, now a distinguished political scientist, teaching at Northwestern. In all of my education up until then, Richard was the first black person that I can remember encountering, not counting Helena Jones at Scarborough School. My family had been a dot of Chinese in a sea of white.

After my good fortune in being awarded the Rhodes Scholarship (and the alternative Marshall Scholarship, which I was counseled to decline), I had to decide on what to do next. The Rhodes offered a graduate education in any subject that I might choose, regardless of what I had proposed in the application. Robert Macdonald, whom I’ve already mentioned as a fraternity brother and friend of mine, had fallen in love with a new field called neuroscience and with born-again fervor saw an opportunity to win another convert. I was resistant, but he simply wouldn’t take “no” for an answer. I had convinced the Rhodes committee that I would gain an Oxford training in solid-state physics, in preparation for a career as a scientist-statesman, perhaps a Presidential Science Advisor or a cabinet member like Steven Chu of today. But Macdonald persisted and eventually beat down my resistance, insisting that at the very least I should seek advice from a famous auditory physiologist named Nelson Kiang. I went to see Kiang, a charismatic and intense researcher, at the Eaton Peabody Lab of Auditory Physiology at Massachusetts Eye and Ear (part of Mass General) that he headed. There, Kiang gave me two pithy pieces of advice: first, learn about evolution; two, seek out Stephen Kuffler. I followed these pieces of advice, and came under Kuffler’s spell (more below). I happily accepted Kiang’s invitation to spend my remaining moonlighting time before Oxford at the Eaton Peabody laboratory.

During spring and summer semesters in 1966, back at MIT after my GE experience I had time to learn some biology. Unfortunately, lacking prerequisites, I was not allowed to take Joel Brown’s experimental course in neuroscience. The best that I could muster was a lab course in microbiology taught by Salvador Luria. There I learned to pipette, using old-school mouth suction to take up solutions, some containing nasty bacteria such as Salmonella. My lab partner, Joseph Malpeli, later a visual neurophysiologist, was infinitely patient and managed during our breaks from pipetting to teach me about the 20 amino acids and why they were interesting. Some evenings were spent working with two young faculty, William Peake and Thomas Weiss. We set out to try to put a microelectrode into a cochlear hair cell, not in a convenient model animal but in the cochlea of a cat, a quixotic project that has never been done to the best of my knowledge—people work with much more reduced preparations. The goal made sense in the abstract because Kiang’s classic recordings from the auditory nerve had been made in the cat, following in the footsteps of Kuffler’s work in the visual system. I fondly remember evenings in the lab with both of them, Weiss made the microelectrodes in a nearby lab, and Peake and I tried to get ready to make recordings. They were both kind and supportive and seemed to enjoy the opportunity to stay out late to guide a naïve student. I also pulled an all-nighter with a master’s student, Michael Wiederholt, who was doing recordings from a cat’s auditory nerve bundle, my first glimpse of in vivo electrophysiology. Enduring my questions was probably exhausting, although he didn’t outwardly complain. I watched Kiang preparing his book on cochlear nerve recordings, laboring obsessively over the massive figures, and was admonished that the traces were as important as the writing. As we approached summer, Kiang gave me a pep talk about being more engaged with the project, but I was distracted while taking German at Harvard Summer School (my only C+, I forgot to study the subjunctive forms of German verbs) and, liberated from the overachiever’s weekly grind at MIT, dating a sweet girl (a judge’s daughter and good person—enjoying, for example, a picnic at the Boston Pops Concert on the Charles River on Bastille Day). I was also preoccupied about what would happen in Oxford.

Your research has mainly focused on various aspects of neuroscience recently. But, as I understand it, you actually started out in cardiac physiology. Can you tell me a little bit about how you got started in cardiac physiology and how you came to change? (Adler, 2015)

My master’s degree in electrical engineering had led to the chance to go to Oxford for a two- or three-year study program with tuition and living expenses paid, an amazing opportunity. But what to do? The two choices presented from Oxford were working on excitable tissues with Denis Noble, who at the time was really just an assistant professor, or on oscillatory contractions of insect flight muscle, with J. W. S. Pringle, a senior scientist and member of the Royal Society. I went to hear Professor Pringle speak but lacked the right background to appreciate his work using x-ray crystallography to get at structural dynamics of muscle cross-bridges at various stages of the contractile cycle. When Pringle, a tall distinguished man with a dry quiet voice (think Dicky Merton in Downtown Abbey), showed diagrams of x-ray intensities in Fourier space, one after another in a dark room, I kept falling asleep. I decided then and there that I was not cut out to work on insect flight muscle, but would take my chances in approaching the young Denis Noble, who had written just one paper on his own, not even an experimental paper but a 66-page review article about the Hodgkin–Huxley equations, describing the dynamics of excitable membranes (Noble, 1966). I wrote to Noble, and, after a long delay, finally got a letter accepting me as a potential graduate student, no conversation, sight unseen. I learned later that the Warden of Rhodes House, Sir Edgar Williams, knew Noble through their joint affiliation with Balliol College and had helped with the arrangements.

Sailing to England

Just as correspondence involved letters, not email, travel to Oxford took place by steamship, not airplane. Thus, I had five whole days to mingle with other members of our class in the relatively luxurious setting of an ocean liner, the Queen Elizabeth. The crossing was rough, and one of our now-renowned classmates, the film director Terence Malick, spent much of the passage seasick in the bar, passing the time by eating peanuts. I met Terry because I had decided to fill the time productively by systematically and earnestly interviewing my classmates to jot down something about their backgrounds. In this way, I met David Kendall, now famous for his high-profile cases as a Washington attorney, some involving the Clintons, and learned that he had been shot at during his voter registration activities in Mississippi. Where did I get the nerve, an MIT electrical engineer, to compile profiles of our band of roughly 30 (out of 32) U.S. Rhodes scholars? I don’t remember feeling any embarrassment back then, just exuberance about the life journey we were all embarking on; I was merely using the time efficiently, gathering data. What else was there to do?

By this time, it was clear that I had somehow opted for roads less traveled: MIT, not Harvard; science, not liberal arts; and rather than Balliol, the academic epicenter of Oxford, Wadham College, a smaller and less famous college nearby, strategically situated partway along a well-worn path between most of the colleges (residences for both students and dons) and the Oxford University Science area. This realization could have dawned even earlier, in Cambridge, Massachusetts, had I attended a meeting for a dozen soon-to-be Rhodes scholars, where I would have been the lone MIT person, all the rest from Harvard. Many of these people later turned out to be friends. Meanwhile, Wadham had a famous and friendly warden (their name for the head of college, not the person at the gate to the college, as I learned the hard way). Sir Maurice Bowra was a renowned classicist, born in China, famous for his independence and quips. Vociferously anti-Nazi, Bowra met Adolph Hitler way early in his rise to power and replied to Hitler’s “Heil Hitler” with an instant “Heil Bowra.”

Bowra’s authentic and eccentric charisma imbued Wadham College with good cheer. There was a nice mix of Rhodes scholars from Canada, Australia, and the United States, including a distinguished Canadian biochemist-in-training, John Bergeron. I enjoyed vacation travel to Ireland with these men, grouped not by our fields but by our status as ex-colonials amidst a landscape of British undergraduates. The locals seemed to read me as American, not Chinese or Chinese American, because of accent, body language, and Yankee brashness. Rhodes scholars were assumed to be competent, older, and replete with odd tribal customs of their own. In 1966–1967, early in the Vietnam War, our antiwar activities included the penning of a letter to President Johnson questioning the wisdom of war that appeared in the New York Times. Mild stuff compared with what was to follow. I was told that my engineering background marked me as too conservative to sign, but I scurried around Oxford in the predawn hours, doing my bit to gather signatures—in the end, 50 Rhodes scholars signed, 20 out of 32 of our 1966 class. A predawn image of awakening Curt Hessler in his underwear sticks with me. Friends like Stewart Early and Wesley Clark stood out as being in honorable opposition to the letter. We all saw this as an honest difference of opinion to be respected, not as polarizing as politics today. My father, by this time a naturalized American, staunchly conservative, was intensely displeased with my signing the letter even though it merely questioned the wisdom of the conflict in a respectful tone.

As a Rhodes Scholar and junior fellow at University College Oxford, Tsien graduated with an Oxford DPhil in Biophysics in 1970, working under the superb mentorship of Denis Noble (a cardiac electrophysiologist) and Julian Jack (a cellular neurophysiologist). His doctoral thesis with Noble described outward currents that support the cardiac action potential repolarization and repetitive firing; Tsien also worked with Jack and Noble on a book, Electric Current Flow in Excitable Cells. (Adler, 2015)

I had never met Noble, and without today’s Google Images, had no idea of what he even looked like. I went to the Oxford lab every day for about a week (no security, one simply walked in), only to be told by Keir Pearson (a Rhodes scholar from Tasmania, now known for his work on motor control) that, no, Denis wasn’t in today. Finally, one day I met him—a slim man with reddish brown hair, pageboy cut, wearing a slightly rumpled yellow tie and proffering a limp handshake to meet my ex-wrestler’s bone crunch. Not much to say except a shy welcome, see you tomorrow. Soon it became clear that although I had intended to work on the brain, Denis Noble was not doing any experiments on neurons or nervous tissue; he was actually studying the electrical basis of the heartbeat. So, I had to choose then and there between working on the brain or joining with Noble in trying to unravel the underpinnings of the cardiac action potential. And, since I knew no biology, everything seemed interesting. This began what proved to be a nearly two-decade detour toward my eventual career as a neuroscientist.

Denis Noble is now a fellow of the Royal Society, recipient of the Order of the British Empire and multiple honorary degrees, and former president of the International Union of Physiological Sciences (IUPS). It’s been more than a half-century since he drove an old car to the 1963 IUPS meeting in Leiden and showed traces of a computed cardiac action potential based on an extension of Hodgkin and Huxley’s equations for squid axon (Noble, 1962). An authentic wunderkind, Noble’s formal advisor was Otto Hutter, celebrated for his work with Wolfgang Trautwein in Steven Kuffler’s lab, recording effects of sympathetic and parasympathetic stimulation on cardiac pacemaker potentials (Hutter and Trautwein, 1956). But Denis’s computations were done on his own (Noble, 1962), with only advice from senior faculty at University College London (UCL). Today, the framework for such computations can be downloaded from the internet by high school students, but in those days, simulation of membrane excitability required sophistication and a struggle to get computer time, and seeing authentic-looking cardiac action potentials was a big deal.

Denis’s donnish outward appearance and eloquent British orations were deceiving; although he had learned to fit in, his roots were humble, east end of London, not really Oxford at all but in some ways the epitome of Oxford. Time in France as a child had given him an affinity for French culture—cooking, literature, and the spoken word. Apart from his brilliance, both in math and in discourse, what set Denis apart was his love of philosophy, and perhaps secondarily, his yen for argumentation on behalf of a cause. Think of a linguistically precise Oxford philosopher rolled up with Joan of Arc, dressed in armor and ready for a righteous battle. All of these traits come together in his advocacy for the culture of Occitania. Activists can derive inspiration from Noble’s current writings in The Music of Life (Noble, 2006), which champions a physiological view of biological systems rather than a narrower “selfish gene” approach (Dawkins, 1989). Denis has fought for public support of science and, in so doing, spearheaded a still-famous academic coup at Oxford that denied Margaret Thatcher an honorary degree because of her draconian policies toward science funding. Denis Noble would be a fitting subject for a full-blown biography or novel.

Denis made no attempt at inculcating me with his personal characteristics, although we spent a lot of time together during our three years together in Oxford while I was his doctoral student. I was treated as a privileged acolyte, friendly colleague, and thirsty sponge for information. Given differences in our roots, and my lack of real biology background, how did I get so much of Denis’s attention? It started with Oxford-style tutorials, weekly one-on-one meetings, going over his approach to membrane excitability. No attempt at breadth—that was for me to get on my own. Denis left Keir Pearson and Dick Stein mostly alone to work on the nervous system—he was (and then we were) going to focus on cardiac action potentials. He showed me how to collect hearts at the local slaughterhouse and to obtain two-electrode voltage clamp currents from bundles of heart muscle cells called Purkinje fibers. But then he hardly appeared in the lab for experiments, for life as an Oxford don was busy, and I seemed to relish experiments. I once asked him where the sheep heart’s natural pacemaker (sinoatrial node) was—he wasn’t sure. Denis left me to make my own mistakes, without much experimental guidance or interference.

Happily, I passionately loved doing experiments and, as his sole source of data, was given tremendous access to analyze and discuss the results with him. We would walk together to the covered market to buy food, chatting as we went along, talking about philosophy as much as science, walking back to his place where I would serve as sous-chef for his evening cooking. This often culminated in his bringing a tray of delicious Indian curry up to the bedroom of his wife Susan, a physiologist in her own right, who coped with depression by reading classic British novels. Often, Denis and I then ate together, continuing our discussions. Sometimes the Indian cooking extended to a dinner party, with Denis providing a variety of dishes and his colleague and friend Julian Jack bringing over a Pavlova, a dessert concoction made of egg white crust replete with cream and passion fruit. I introduced Denis to guitar playing, which he took up much more seriously than I later on. Our social life extended to a vacation together in 1968, on Lake Windermere in England’s Lake district, a two-car party with Denis, Susan, and their daughter Penny, my then-girlfriend Jane and myself, and Julian Jack and Steven Redman. Each scientific pair was working on a manuscript, pivotal work that would appear in the Journal of Physiology, our top-tier venue for longer publications (Jack and Redman, 1971a, 1971b; Noble and Tsien, 1969a, 1969b). Some time later, my future wife Julia and I would join Susan and Denis to attend an Oxford ball—an all-night party with dancing and champagne. Susan entertained us with risqué stories of their courtship, providing salty humor to counterbalance Denis’s shy formality. I mention all this to convey how personal interactions intertwined with scientific advances, a kind of life experience that is much harder to imagine today. When I began work in his lab, I was 21 and Denis was 29.

I vividly remember a particular experiment, #78-1, that yielded the bulk of the data for the story written up at Lake Windermere. Over the course of a singularly long (4 hour) recording from cardiac bundles, I obtained a complete dissection of two components of outward current, at various times known as Ix1 and Ix2, IKr(rapid) and IKs(slow) or hERG and KVLQT1 (we got most of the basic properties right but lost the naming battle and most of the credit). I had a date with Jane, who was an anthropology doctoral student, and I had to stand her up to finish the experiment (no cell phones), but she understood its importance and accepted my apology. Now that we knew how IKr and IKs could be separated, I handed Denis the multiple rolls of heat-sensitive chart recorder paper, challenging him to do the analysis, a task with lots of plotting on semilog graph paper that I knew he would enjoy. An equally thrilling set of data, on epinephrine’s effect on cardiac pacemaker current, had come off the chart recorder about a year earlier. Both of these findings were somewhat heretical: our emerging picture of multiple types of potassium channels was different than Noble’s own model and clashed with preconceptions based on the simpler workings of the squid axon. Nowadays, folks accept without question that heart cells display a rich diversity of outward currents (Chiamvimonvat et al., 2017; Nerbonne and Kass, 2005), but this seemed implausible at the time. The finding of a neurotransmitter modifying a voltage-gated channel by shifting its voltage dependence (Hauswirth et al., 1968) was also quite novel compared with acetylcholine quickly activating a ligand-gated conductance (studied by those whom Kuffler termed “millisecond men”). Denis and I believed in our data and weren’t fazed by coming up with oddball findings. The experiments on K currents supporting the cardiac plateau and neuromodulation of pacemaker current would form the basis of later work in my own lab.

Steve Bergman (a.k.a. Samuel Shem)

I simplified the reality in saying that Noble had only me to look after. Perhaps the most fascinating part of the story was his other doctoral candidate, from the same boatload of U.S. Rhodes scholars, Steven J. Bergman. Little did any of us know that under the pseudonym Samuel Shem, Steve would later publish the famous House of God, a classic novel about medical training that has sold more than two million copies and was put on a par by John Updike with Joseph Heller’s Catch-22. Chunks of hospital slang that he invented are now used in practice. Steve and I became acquainted on the Queen Elizabeth, when I learned that he had played basketball at Harvard and was headed to Balliol under the supervision of the self-same Denis Noble. Moreover, Steve had worked on the brain, specifically, on the role of calcium in memories. In Dan Pollen’s lab at Harvard, Steve had used his fine motor skills to cannulate blood vessels in the brain to manipulate the calcium in blood, looking for a change in the encoding of memories. Retrospectively, one could argue about whether the experiment would work in practice, because intracellular calcium is so tightly regulated, but there’s no doubt of its prescience. Once at Oxford, Steve read Samuel Beckett and wanted to write plays, not do experiments, although he was canny enough to follow in Keir Pearson’s footsteps and complete his doctorate on a physiological aspect of a simple form of memory, conditioning of the leg-lifting behavior of a cockroach. Just as Noble was incredibly kind to me, he also forever shaped Steve’s life by simply allowing him to do his own thing, guilt-free.

Coincidentally, I eventually worked on the role of calcium in memory, and Steve went on to become a psychiatrist and famous author and deliverer of inspiring graduation speeches. Steve/Shem’s cynical, irreverent, sexy, but ultimately hopeful novel House of God helps many medical students get through their training (I even had the pleasure of prescribing House of God to one of my own students in his darkest days of working in Bellevue Hospital). To complete the ironic arc, Steve Bergman is currently a clinical professor in medicine and psychiatry at NYU, which recently celebrated the 30th anniversary of House of God, featuring the real-life counterparts of his intern characters. With his partner Janet Surrey, Steve wrote a prize-winning play about the founders of Alcoholics Anonymous, Bill W. and Doctor Bob, that galvanizes community groups fighting alcoholism. Steve has just come out with a sequel to House of God, entitled Man’s 4th Best Hospital. No longer denounced by the medical establishment, a chapter from Man’s 4th Best Hospital was published verbatim in Journal of the American Medical Association. The novel contains a female character, Rosie Tsien, modeled after me, and a fictional discovery based on our shared interest in calcium and memory and my current work. Novelists struggle even harder than researchers to get published and read, but they have special powers. I love Steve’s fictionalized stories about raising his adopted Chinese daughter, called Spring in the novel, which resonate with my personal experience; I am thrilled that Spring and Rosie get to interact. But foremost in my mind, beyond my surprising inclusion in someone else’s fiction, is something that Bergman has long since forgotten: his kindness to me after my first biological seminar, on using Eyring’s rate theory ideas to think about the energetics of channel opening and closing (Tsien and Noble, 1969). This was a full-blown departmental seminar by a mere doctoral candidate, another occasion in which Denis Noble blithely allowed me a risky opportunity, a chance to fail in presenting my upstart ideas. What I remember about the talk were the rookie mistakes I made in fielding the questions and how afterward Steve, in full future-psychiatrist mode, reminded me of the upside. It is part of Denis Noble’s legacy that he shaped Steve’s and my careers so profoundly, without appearing to think hard about it. Because my memory of that seminar, and Denis’s and Steve’s roles, has been retrieved, considered, regretted, and put away again for five decades, it may be in my top 10 to hang on to when Alzheimer’s sets in.

Julian Jack as a Special Mentor

Julian Jack was my other scientific parent-slash-older brother during these formative years. A New Zealand Rhodes scholar, Julian was a fellow of University College Oxford and had a lab in the Physiology Department, working on spinal cord neurophysiology. Neurotree traces Julian’s lineage back through Archie McIntyre to Sir John Eccles; thus, through Julian, I am in Eccles’ line and a distant cousin of Roger Nicoll, who is proud to have worked directly with Eccles. As junior faculty, Julian and Denis respected each other and were both known for their youthful brilliance in a conservative Department of Physiology, headed by G. L. Brown and later David Whitteridge. In the late 1960s, long before they ascended to central positions in Britain as fellows of the Royal Society and leaders of the Save British Science movement (Noble) and of the Wellcome Trust (Jack), Denis and Julian could still regard themselves as outsiders.

This was only partly true in Denis’s case, because he was well known and respected by the British establishment through his UCL and Hodgkin–Huxley connections. As a New Zealander, Julian was one step further removed, and by nature, took a critical view of orthodoxy. His tutorials with me were about vision and presented a balanced picture of what Hubel and Wiesel had and had not done. Although I was ostensibly a researcher in cardiac physiology, Julian took the time to expose me to systems neuroscience and its underlying connections to cellular biophysics. With his New Zealand education, medical degree, and Scottish genes, Julian could be disapproving of people taking shortcuts in life. He once made me back up a glib but correct statement with a full-on blackboard derivation invoking the superposition principle. He frowned upon Steve Bergman’s hiring another person, an MIT grad, to do computer programming for his thesis. Julian was tough on people whose work appeared superficial—sometimes he may have thought that about some of my research with Denis. Like a stern brother, he didn’t use much overt praise—“able” was the best rating that he ever gave me directly—but like Mrs. Helena Jones, he knew that this form of tough love was both effective and appreciated. Thanks to Julian Jack’s encouragement and recommendation, I was elected a junior fellow two years before finishing my doctoral work, enabling me to dine and interact with the faculty in his college, University College Oxford (Univ). Not only did I have a chance to chat with distinguished scholars like John Albery, H. L. A. Hart, and George Cawkwell, but also I caught up with some of the worldly knowledge and scholarly breadth that I had missed by going to MIT rather than Harvard.

University College housed many social groups humming along intensely without much interaction. While dining with the dons, I also hung out with expat Americans in the same college. For example, the Rhodes scholar class of 1968 stands out in my mind because they were more galvanized with antiwar fervor than those that came before them. Each class that came along was more and more militant. University College was home to Bill Clinton, Robert Reich, and John Isaacson. I remember meeting them at a mixer in Univ, upon my transfer from Wadham and their arrival to Oxford. Bill Clinton wore a war surplus jacket and was a friendly, confident, an attentive listener. I was dismayed when Bob Reich disparaged my Rhodes career path as that of a “technocrat,” not realizing that his picking an argument with me was a surefire way of starting up a conversation, a form of intellectual engagement. Clinton, Reich, and I would wind up at Yale at the same time, and Reich and I would live in the same house for two years. In the fall of 1968, the Vietnam War was on everyone’s minds. No one knew what anyone was going to do.

All of these vivid Oxford experiences in University College would not have transpired without Julian Jack’s intervention. Julian’s Wikipedia entry cites his celebrated doctoral students, Michael Hausser and Dimitri Kullmann (who, like Jack, are both members of the Royal Society), but has no mention of his lifelong partnership with Steven J. Redman, an electrical engineer turned electrophysiologist who spent years with Jack in Oxford (Jack et al., 1971; Jack and Redman, 1971a, 1971b). This was a match made in heaven, a pleasure to watch. Steve Redman was like another older brother to me, both kind and stern all at once. It gives me great joy to have spent time studying synaptic transmission and dendritic properties, a field that they helped pioneer along with Wilfrid Rall (Rall et al., 1992).

Jack and Noble Provide Perspective on the British Physiological Establishment

As young faculty, Denis Noble and Julian Jack organized an unconventional seminar series that met on Saturday mornings and gathered Britain’s best and brightest. Oxford was central enough to access from other centers of physiology and biophysics. We heard talks by Horace Barlow, Colin Blakemore, William Rushton, Fergus Campbell, Ainsley Iggo, Jack Diamond, Richard Adrian, Richard Keynes, and Roger Thomas, to name a few, without concern about any conceptual separation of biophysics, physiology, and neuroscience. As a student of both Noble and Jack, with a natural inclination to ask questions encouraged at MIT, I had many chances to interact with the British scientific establishment. The Saturday seminars and regular meetings of the Physiological Society gave me opportunities for one-to-one interactions with Alan Hodgkin, Andrew Huxley, and Bernard Katz and thus a personal bridge to British physiology at its best. I can illustrate this with interactions with Peter Baker, the scientist who took squid giant axons, extruded the axoplasm from them like toothpaste and showed reconstitution of excitability upon refilling with artificial solution (Baker et al., 1961). We met in Aberdeen Scotland at a Physiological Society meeting, my first presentation of an abstract. Baker was working with Hodgkin and Mordecai Blaustein on the sodium pump. Parched for biophysically minded colleagues at the small, remote meeting, he drew the figures of their nascent paper on index cards—lots of saturating functions showing how flux varied with ion concentration. This interaction led to a memorable day when he kindly came from Cambridge to Oxford to pick me up before continuing down to Plymouth in England’s southwest corner, an all-day drive. I don’t remember what we chatted about along the way, but I appreciated that I was receiving special treatment from a member of the Cambridge establishment. Baker had so much pent-up desire to experiment that he began dissecting an axon almost immediately upon arrival at the Marine Station. Even more myopic than me, Baker’s nose was practically pushed up against the specimen. That evening, I was to meet someone who became a lifelong friend, Larry Cohen.

It was Andrew Huxley, not Alan Hodgkin, who had been Noble’s role model at UCL. He was the most feared of the British physiological elite. Forewarned by Denis about his long silences, I found him to be much more approachable than reputed. He actually liked being asked direct questions, especially if they were intellectually challenging. He clearly appreciated the attention conferred by his Nobel Prize, but felt that his scientific big brother Hodgkin had overshadowed him in the field of excitability, and he made no bones about wanting to win a prize on his own. I once asked Huxley a question about the position-dependence of cross-bridge attachment, drawing a natural analogy to the voltage-dependence of channel opening in excitable membranes. Decades later, his colleague Robert Simmons reminded me of this question, and let me know how much it annoyed him, perhaps thinking protectively that Huxley would find it awkward. I also remembered the question, but recollect that Huxley answered it with delight, as if someone out there were curious about a recurrent theme in his scientific life.

As a German refugee, Bernard Katz was one of a highly distinguished group of European scientists who had found their way to the United Kingdom and had seemingly been well taken care of. I have written elsewhere about Katz’s seminal discoveries and the tortuous history of calcium channel discovery (Tsien and Barrett, 2004). Around 1990, I met Katz in his office in UCL after my lab had started work on calcium channels, neurotransmission and long-term potentiation (LTP). I remember him as very curious, thoughtful, precise, and modest. Here, I’ll simply mention that his compact primer on cellular physiology, the renowned Nerve, Muscle and Synapse (Katz, 1967), was a big early influence, and a paperback copy was my early gift to my future wife Julia Shiang when she came to Oxford to study biochemistry for a junior year abroad. Julia means the world to me—I have many stories about our 51 years together that I’ll save for a family document in which space is not limiting. For now, suffice it to say that giving Katz’s book to Julia was the highest token of courtship. I would like to acknowledge Katz and his friendly competitor and admirer, Chuck Stevens, for motivation to work on mechanisms of transmitter release, vesicle fusion, and postsynaptic responses.

Most neuroscientists tend to focus on the most famous contribution of individual researchers, sometimes forgetting other contributions cast in the shade of the biggest discovery. In the late 1960s, in the wake of Hodgkin and Huxley’s 1963 trip to Stockholm, and before Katz’s 1970 prize, each of the three had turned their attention to downstream consequences of excitability, what would now be called excitation-response coupling. Hodgkin worked on muscle activation, including the surface action potential and radial spread of depolarization (Adrian et al., 1969, 1970a, 1970b), as mentioned earlier. Huxley made significant contributions to understanding muscle activation (Huxley and Taylor, 1958) but then went on to muscle contraction itself (Huxley and Simmons, 1971). Katz had already switched to synaptic transmission as studied at the neuromuscular junction and later, the squid giant synapse (Katz and Miledi, 1971). Looking back on this, there may have been some attempt to give Bernard Katz a shot at his own place in the sun. Rodolfo Llinás once told me that Eccles asked him to wait a season before starting experiments that would compete with Katz and Miledi’s work on the squid giant synapse (although famously fierce and independent, Llinás graciously complied).

An Early Opportunity to Teach Physiology

During my fourth and last year in Oxford, Denis Noble took a sabbatical in Edmonton, Alberta, where Keir Pearson and Dick Stein had gone as faculty members. This gave me the opportunity of taking over Noble’s teaching, even though I hadn’t yet completed my doctorate. I gave his cardiac lectures and took over some of his tutorials, another opportunity for which I owe Denis. The tutorial system put me in one-on-one contact with students who were bright but not necessarily very motivated, so I could in some cases play the role of my high school math teacher Helena Jones. Happily, all three students that I tutored got a “first,” the top grade. When it came time to present my dissertation, I received permission to bind four of our papers together with an introduction. Defending the thesis took place after lunch with my examiners, Humphrey Rang and Richard Adrian, arranged by my substitute doctoral advisor, a feistily charming Scottish don named Jean Bannister in her home base, Somerville College. At lunch, Julian Jack plied the examiners and me with multiple bottles of wine to get everyone loose. The exam, in a hot closet-size space, was much less memorable, but I recall Richard Adrian pointing out in good humor that it wasn’t clear who was examining whom. As Alan Hodgkin’s colleague, his cheerfulness was an extension of Hodgkin’s earlier kindness, supplemented by Adrian’s natural flair for mentoring.

Richard Adrian as a Beneficial Influence on Two Brothers

Later, Adrian would become Roger Tsien’s supervisor at Churchill College Cambridge (Tsien, 2010). Roger managed to steer safely clear of me (and Louis Tsien, our middle brother)—Harvard, not MIT; Marshall, not Rhodes; Cambridge, not Oxford. But his own doctoral trajectory would put him into the orbit of the very same Cambridge scientists that I had known: Adrian, Hodgkin, and Richard Keynes, who took him on at Cambridge, seemingly without hesitation. Determined to make his chemical prowess pay off physiologically, Roger worked at first on synthesizing pharmacologically active derivatives of tetrodotoxin (Tsien et al., 1975). Later, joining forces with Timothy J. Rink on nonexcitable cells proved to be one of Roger’s break through career moves (Rink et al., 2016; Tsien, 2010). Just as Roger’s journey connected classic British neurophysiology with modern fluorescent indicators (Zhang et al., 2002), my own career has linked the same small band of scientists to modern optogenetics, through my former graduate students Karl Deisseroth and Edward Boyden, and a former course student, Feng Zhang (Boyden et al., 2005; Zhang et al., 2006).

Joining the Yale Faculty

I went straight from Oxford to an assistant professorship at Yale in 1970, in the middle of the Vietnam War. Skipping the postdoc stage was not the most conservative strategy, but I did it partly to avoid the military draft. As a 25-year-old, I was approaching the end of my educational deferment (age 26). My new physiology chair, a renowned kidney physiologist named Gerhard Giebisch, had offered the job to Harald Reuter, but Harald had an offer in Europe, turned down the Yale position, and graciously recommended me for the job. I first met Reuter at a memorable Gordon Conference, where I presented our work on cardiac repolarization (more about Reuter later). Here is direct quote from a letter I wrote to my parents at the time (March 23, 1969):

A flurry of scientific visitors arrived. A man named Reuter, who I’d met in N.H., and a Japanese called Tomita—both very capable and pleasant. Denis, Otto and I entertained them for two days of very hectic conversation, and a Chinese meal. Then, two days of Physiological Society meeting in London, and more talks. . . . Reuter, in fact, was almost to [the] point of accepting the job at Yale this summer, but changed his mind when offered a professorship in Bern, Switzerland. The environment at Yale was better, he thought, but he was concerned that his children should become utterly Americanized—there were already signs of this after a year at the Mayo Clinic. And so, he wrote to the head of the department at Yale and suggested that they ask me! It’s nice to have scientific friends, especially when they are as honest and straightforward as this man is. We are also in [the] peculiar position of being able to appreciate each other’s work.

Knowing that during my post–Gordon Conference tour I had looked at good places, including Penn and UCLA, Giebisch sent me a telegram offering me the job at Yale, sight unseen, urging me to fly over to visit to seal the deal. Lest this seem a precipitous gamble on their part, the slot was for the time-sensitive replacement of a retiring professor and the startup package was $15,000. Upon visiting, I instinctively trusted Gerhard Giebisch and I had already met and liked Knox Chandler, one of Hodgkin’s colleagues at Cambridge, and Larry Cohen, who had put me up at Plymouth Marine Station after my long drive with Peter Baker. Thus, I accepted Gerhard’s offer on the spot, without any negotiating or even seeing the lab space. This seems incredibly naïve in retrospect, but like other quick decisions in my life, it happened to turn out well, after a few scary bumps. I would remain on the faculty at Yale for 18 years. During that time, I made a transition from cardiac electrophysiology to working on neurons and studying neuronal ion channels. This wasn’t nearly as drastic as it sounds because channel modulation and calcium signaling remained universal themes throughout.

Because I am leveraging my limited personal experience to sketch out the scientific scene in 1970, let me spell out how close-knit these admittedly privileged institutions were. Chandler had worked directly with Hodgkin (Adrian et al., 1969); Cohen under Richard Keynes (Cohen et al., 1968); A. R. (Bob) Martin at Yale had been a postdoc in Bernard Katz’s lab in University College (Boyd and Martin, 1956); and Gerhard Giebisch had performed early voltage clamp recordings of putative calcium currents in Bern with Silvio Weidmann (Giebisch and Weidmann, 1971), Hodgkin’s main cardiac disciple, a pioneer in his own right, and a caring scientific uncle to me. Giebisch’s predecessor at Yale, Carlton C. Hunt, had published classic papers with Kuffler (Kuffler and Hunt, 1952). Denis Noble was a disciple of Huxley, and so forth. Neurotree depicts scientific lineages, but historians of science might well consider departmental groupings like those in Cambridge, Oxford, Bern, and Yale, and biological kinship as well. Richard Adrian studied with Hodgkin, but his biological father, Nobel laureate E. D. Adrian, who had shown that biological systems can encode natural stimuli in trains of impulses, was Hodgkin’s mentor. Richard Keynes’s middle name, Darwin, acknowledges his great-grandfather Charles. British physiology in the late 1960s was a veritable scientific greenhouse, producing seedlings not only for England but also for export to the United States and Germany.

Ferment at Yale in Early 1970s

Although I abandoned any thought of a career juggling science and politics, life as a junior faculty member Yale had its real-world, political aspects. My acquaintance with H. L. A. Hart morphed into encounters with Guido Calabresi, a legal scholar at Yale on a Rhodes selection committee. As a precocious faculty member, I naturally gravitated to peers who were students in professional schools. Whereas I had already decided what I wanted to do—to study neuromodulation and signaling—they weren’t so sure about their goals. Steven Bergman and our mutual friend William Clark went to medical school at Harvard and later lived the uncertain life of the House of God. Our legally or politically minded Oxford acquaintances mostly wound up at Yale (or Harvard) law school, or so it seemed. Several people I saw most often, David Kendall, Bill Clinton, and Curt Hessler, were all Yale law students. I lived in a house with Robert Reich and another charismatic law student named Nancy Bekavec, who later became head of Scripps College. Our other housemate, Maura Smolover, designed beautiful sets in the drama school, and we made dinners together in a house in downtown New Haven in one of several sketchy neighborhoods where I lived, later with Julia. Although I could have retreated to a purely monkish existence in the lab, I was stimulated and distracted by the tumultuous atmosphere in New Haven, a community imbued with antiwar sentiment and featuring already emerging stars like Hillary Clinton, Meryl Streep, and Christopher Walken. At a personal level, Yale was a continuation of Oxford except that I now had a real job and had to prove that I could do research on my own.

Not Good at Starting a Lab

Then reality set in. I felt very welcomed by the Yale Physiology Department, but the available space was a large room in the basement that lacked windows: no natural light whatsoever. We painted the walls blue. Lacking postdoc experience or any serious mental preparation, I was pretty bad at beginning my own lab. To begin with, I wasn’t so good at the biology, having missed out on medical school and a real graduate school; I made many rookie mistakes. It took many trips to a slaughterhouse miles outside of New Haven before I got healthy Purkinje fiber recordings. A new doctoral student, Wayne Giles, barely two years younger than me, had worked with Susan Noble in Oxford for a master’s degree and had a much better idea of how to get the lab going. Unfortunately, Wayne felt isolated in New Haven (which he perceived as too much like New York City!) and missed his Canadian sweetheart. He went home during one winter break without letting me know he was leaving the lab. This was devastating to me. Wayne came back later from Canada to defend his thesis and went on to become a distinguished endowed professor and dean in Canada.

What saved me then was that I was good at recognizing talent, teaching what I did know, and picking juicy basic problems that had some degree of clinical significance. I took on Robert S. (Rocky) Kass as a postdoc and W. Jonathan Lederer as an MD-PhD student, both only a year younger than me. We and our spouses got along well socially. Rocky and Jon later went on to positions of scientific prominence and leadership at Columbia and University of Maryland, building in innovative ways on the basis of their early interests in our group at Yale. It was a good thing for all of us that they seemed unconcerned about the career risk of joining such a young lab.

Adler: You actually stayed in cardiac physiology for quite a while.

RWT: The problems that we were working on were so fascinating that I couldn’t resist the idea of staying there. (Adler, 2015)

It made sense to study ion channel modulation in heart cells. Personal experience tells us that the rhythm and strength of our heartbeat come under powerful control by our brain. My work with Noble in Oxford had vividly demonstrated that adrenaline, a cardiac accelerator, modified the voltage-dependence of a voltage-gated channel by shifting the midpoint of its activation curve toward more depolarized potentials (Hauswirth et al., 1968). Harald Reuter had shown that inward plateau currents, putatively carried by calcium ions, were augmented by adrenaline (Reuter, 1967). I was keen to delve more deeply into the mechanisms of these observations in my own lab at Yale. Did adrenaline (also known as epinephrine) modify the electrical field felt by the voltage sensor of the pacemaker current (Tsien, 1974b) or did the neuromodulator act through a second messenger system involving a newly discovered intracellular messenger, cyclic AMP? I tried to answer these questions with experiments in Purkinje fibers, my only solo experimental papers (Tsien, 1973, 1974a, 1974b). Phosphodiesterase inhibitors that lacked net charge evoked the same voltage shift and occluded the effect of adrenaline, arguing against an electrostatic mechanism and in favor of a scenario involving cAMP (Tsien, 1974b).

I had stimulating conversations with Paul Greengard, who assigned his technician Michael Schorderet the task of assaying cAMP in Purkinje fibers. Though the assays were never successful, Paul passed on a career-long fascination with the power of phosphorylation. Together, we published a paper in Nature New Biology on the role of cAMP in adrenergic modulation (Tsien et al., 1972). Not entirely trustful of experiments using butyryl derivatives of cAMP, my further contribution was to test directly the impact of cAMP elevation, by introducing it via iontophoresis from an intracellular microelectrode (Tsien, 1973). Later, I teamed up with Robert Weingart in Bern to show that radiolabeled cAMP readily diffused from cell to cell within bundles of cardiac muscle cells, thus acting as an intercellular messenger (Tsien and Weingart, 1974, 1976). We observed an increase in the strength of contractions as well. Our experiments on cAMP prompted Harald Reuter to show that dibutyryl cAMP augmented putative calcium currents. He generously offered us co-authorship of his 1974 paper (Reuter, 1974), but we declined, having not contributed directly to the experiments, only to their framing. Looking back on this early era, I am pleased to see my choice of an intriguing problem and implementation of direct approaches but cognizant of how uptight I was about questions of authorship. But this reflected the purist spirit of the British labs I most admired.

Controversy about Calcium Currents

Among neuroscientists, my lab is strongly associated with calcium channels, but at the time of arriving at Yale, this was not a major focus. Toward the end of my job seminar at Yale, which described how cardiac action potentials repolarize (the area broken open by experiment #78-1, written up in the Lake District vacation with Noble), Gerhard Giebisch gently pointed out that my talk had focused exclusively on the roles of potassium currents, with nary a mention of calcium currents that he had worked on with Silvio Weidmann (Giebisch and Weidmann, 1971).

At the time, the very existence of calcium currents was controversial. Ted Johnson and Mel Lieberman were excoriating researchers using existing methods to attempt to distinguish fast sodium currents from kinetically slower currents assigned to calcium influx (Johnson and Lieberman, 1971). Reminding us that the squid axon managed perfectly well to spike with only sodium and potassium channels, Johnson and Lieberman argued that calcium currents were artifacts of poor voltage control. Harald Reuter came under particularly heavy fire, stirring my sense of loyalty to Reuter and Noble-like zest for debate. Through the late 1970s, my group worked earnestly on various multicellular preparations to improve the ability to isolate sodium and calcium currents. We adapted the three-microelectrode method of Adrian, Chandler, and Hodgkin to measure axial voltage drops as measures of inward membrane current (Kass et al., 1979). Sensitized to the problems inherent to heart cell bundles with narrow extracellular spaces, we developed rabbit Purkinje fibers as a system for studying fast sodium currents (Colatsky and Tsien, 1979). Using this preparation, a study on the mechanisms of a local anesthetic block of sodium channels by Bruce Bean and Charles Cohen (Bean et al., 1983) has been heavily cited and helped launch two outstanding careers in academia and industry.

The criticisms fired off by Johnson and Lieberman were neither diplomatic nor completely wrong. Indeed, problems of ion accumulation and depletion blemished some of the work Noble and I had done in Oxford (Noble and Tsien, 1968), to my later chagrin. In contrast, despite relatively primitive methods, the studies at Oxford and Yale were successful enough to identify many of the cardiac ionic current components that are featured in textbooks today, even though our original observations are often not cited (Hauswirth et al., 1969; Noble and Tsien, 1969a, 1969b; Siegelbaum and Tsien, 1980). I gleaned valuable life lessons: don’t expect to get credit for work unless it is more than 90% correct, pick a simple memorable terminology, and be grateful for a little bit of luck. Slack we were not cut for cardiac currents came back with dividends for neuronal channels once our lab became better known.

Advent of Single-Cell and Cell-Attached Patch Clamp Methods

Much of the painstaking work with microelectrodes was swept away by the advent of dissociated cells, single-cell methods, and single-channel recordings. Suction pipette methods of Kostyuk’s group were quickly followed and overshadowed by Erwin Neher and Bert Sakmann’s Nobel Prize–winning patch clamp method (Hamill et al., 1981). I remember walking along Frontage Road behind Yale Medical School when Erwin told me of his findings on single acetylcholine receptor channel recordings with Joe Henry Steinbach in Chuck Stevens’s lab (Neher and Steinbach, 1978). Even before the gigaseal–patch clamp revolution, Kai Lee brought to us methods for dissociating heart cells and recording from them with suction pipette from A. M. “Buzz” Brown’s lab at Galveston. We used these recordings to show that calcium channels can support outward currents, thus defining their extreme selectivity for calcium over monovalent ions (Lee and Tsien, 1982). We also showed that all of Albrecht Fleckenstein’s “calcium antagonists” acted in a use-dependent manner (Lee and Tsien, 1983), not unlike local anesthetics acting on sodium channels. Soon thereafter, Harald Reuter invited me to come to Bern to work with him, Chuck Stevens, and Gary Yellen in trying to record calcium channels in tissue-cultured cells.

I am quite nostalgic about these experiments with Harald, Chuck, and Gary, both for the thrill of seeing single L-type channels opening and closing and for the human interactions. We worked as a team—some days, Chuck would make and fill pipettes with isotonic BaCl₂ and gingerly hand them off to whichever of us was at the rig. One day, while Chuck and Harald were away, Gary Yellen and I had our best experiment on channel inactivation, good enough to dominate a whole figure of our later Nature paper (Reuter et al., 1982), and we followed it up by celebrating his 21st birthday with my wife Julia. Chuck, his wife Jane, and daughter Megan invited us all over for Thanksgiving, making considerable effort to get traditional fixings even in Switzerland, and Chuck entertained our one-and-a-half-year-old daughter Sarah by jingling and exchanging his car keys. A father of three daughters, Chuck never seemed to tire of handing off the keys, nor did Sarah.

Calcium Channel Selectivity and Permeation

Peter Hess capitalized on the advent of gigaseals and our experience with Ca2+ electrodes by putting the Ca2+ sensitive resin in a patch pipette and accessing intracellular Ca2+ levels. I thought this would be a natural project for Peter to follow up, given his background in intracellular Ca2+ regulation, but he got very angry at me and fiercely expressed his desire to be at the heart of the action on single-channel studies. We informed Erwin Neher of Peter’s promising lead on intracellular ion measurements but never followed it up; Peter got his wish and the rest is history (Hess et al., 1984; Hess and Tsien, 1984; Nilius et al., 1985).

Everyone who met Peter Hess would attest that he was a brilliant and strong-minded scientist. After attaining the rank of full professor at Harvard, he died of glioblastoma in his early 40s. As a postdoc in our lab, he tackled the question of how calcium channels can be extremely selective for calcium ions, yet support a rapid rate of ion transfer. Other groups, having observed a saturating relationship between external Ca2+ concentration and channel flux with half-maximal flux in the ∼10 mM range, conceptualized permeation in terms of divalent cation interactions with a low affinity binding site (Hagiwara and Byerly, 1981; Kostyuk, 1981). Millimolar Ca2+ also reduced the flux of Ba²⁺ or Sr²⁺ ions (Vereecke and Carmeliet, 1971). We found, however, that merely micromolar Ca2+ sufficed to half-block the current supported by Na+ or Li+ ions, fitting with the channel’s high selectivity. Hess and I reconciled these observations by constructing a model of the pore, whereby ions move single file, like gramicidin or K+ channels (shades of Hodgkin and Keynes). We proposed that occupancy of a high-affinity site by a single Ca2+ suffices to prevent Na+ flux, while raising Ca2+ to millimolar levels drives pore occupancy by two Ca2+ ions and high rates of Ca2+ influx (Hess and Tsien, 1984). McCleskey and Almers independently proposed a similar model (Almers and McCleskey, 1984). Their group had additional evidence that the pore was wide enough to accommodate tetramethylammonium and could exclude sieving as a mechanism of Ca2+ selectivity.

Fast forward a decade to the mid-1990s, when L-type channels had been cloned and sequenced. Jian Yang, Patrick Ellinor, Ji-Fang Zhang, and William Sather were all keenly interested in the molecular basis of Ca2+ channel selectivity and permeation, a lot of horsepower for one problem. Now we could show directly, using Ca2+ channels cloned by Numa’s group, that a high-affinity site for Ca2+ binding depended on four conserved glutamate residues in homologous positions in each of the four repeats of the pore-forming CaV1.2 subunit (Ellinor et al., 1995; Yang et al., 1993). This led to a revised model in which (1) the ion permeation pathway is much wider than the diameter of Ca2+ or Na+ (both 2 Å); (2) that acidic side chains, be they glutamates or aspartates, protrude into the pore and provide a flexible complex to closely coordinate one or more Ca2+ ions when these are present; (3) selectivity arises because monovalent ions like Na+, Li, or K+ cannot leapfrog ever-present Ca2+ ion(s); and (4) rapid throughput of ions is possible because a newly incoming Ca2+ can loosen the affinity for an already present Ca2+ further along the permeation pathway (Ellinor et al., 1995; Yang et al., 1993). Others have made compelling arguments to add to an emerging consensus (Armstrong and Neyton, 1991; Dang and McCleskey, 1998; Kuo and Hess, 1993; Sather and McCleskey, 2003; Yue and Marban, 1990).

Today, a full 36 years after the 1984 proposals from Yale and UW, a trio of three-dimensional (3D) structures are now available for voltage-gated calcium channels, two for an L-type channel (CaV1.1 from skeletal muscle, characterized with 0.5 mM and 10 mM external Ca2+), and a T-type channel (a cloned CaV1.3 subunit). These cryo-EM structures all come from the amazing work of Nieng Yan and colleagues (Wu et al., 2016; Wu et al., 2015; Zhao et al., 2019). The 3D structures indicate that our ideas were basically right: the pore contains at least one Ca2+ ion even at 0.5 mM external Ca2+ and two closely spaced Ca2+ ions at 10 mM Ca, consistent with both a high-affinity site and the possibility of multiple divalent cation occupancy. The overall permeation path shows no hint of an additional divalent cation binding site distant from the EEEE locus. The pore is relatively wide, although not quite as wide as predicted from organic cation permeation. The pore size of CaV3.1 (EEDD) is actually smaller than that of CaV1.1 (EEEE), as we predicted based on organic cation permeation (Cataldi et al., 2002). Despite the large pore size, the Ca2+ ion(s) are largely if not entirely dehydrated. Glutamate side chains protrude into the pore lumen and help make up the high-affinity site (though these side chains were not well resolved in the first structures), thus providing the carboxylate groups to coordinate the Ca2+ ions. The four repeats show clear asymmetry, I-III being different than and dominant over II-IV (Chen et al., 1996; Chen and Tsien, 1997; Ellinor et al., 1995; Yang et al., 1993). Carbonyl oxygens from the amino acid one position past the key glutamates also contribute to Ca2+ coordination, as Sather’s group has reported (Williamson and Sather, 1999). Like my group, other labs contributing to this field (Armstrong and Neyton, 1991; Dang and McCleskey, 1998; Kuo and Hess, 1993; Sather and McCleskey, 2003; Williamson and Sather, 1999; Yue and Marban, 1990) can all take heart from substantial vindication of their contributions to understanding what makes a calcium channel a calcium channel.

Modes of Channel Gating as a Basis for Modulation by Drugs and Neurotransmitters

Our lab has long been interested in state-dependent interactions between channels and modulatory agents, such as transmitters, hormones, agonists, and antagonists. A general theme not unique to calcium channels is that these agents preferentially interact with particular states of the channel and therefore act in time- and voltage-dependent manner. This is certainly true of antiarrhythmic agents, such as lidocaine for sodium channels and “calcium antagonists” for calcium channels.

Calcium channels not only undergo rapid switching between closed and open states of the channel but also display higher-order transitions between different patterns of gating, something we termed modes of gating (Hess et al., 1984). We observed striking examples of this in unitary patch clamp recordings, whereby a single channel suddenly changes its open probability from hardly open at all (low Po) to strongly open (high Po). A variant on nifedipine known as Bay K 8644 greatly increased the chances of the high Po mode and thus increased calcium influx. This was both a conceptual advance in illuminating an elegant way of modulating calcium influx—channel phosphorylation by protein kinase (PKA) or Ca(2+)-calmodulin stimulated protein kinase II (CaMKII) did much the same thing. Modal gating was also a methodological gift because long channel openings in the high Po mode also opened the way for scrutiny of detailed properties of the open state, including the flux rate of permeant ions like Ca²⁺ and Ba²⁺ the moment-to-moment blockade by impermeant ions like cadmium (Cd²⁺). I vividly remember arriving at a meeting, fresh from airport with luggage in tow and hearing Casey van Breemen talk about the Bay K drug, filled with excitement in anticipating what a boon it would be. Nowadays, we know that Bay K 8644 has a binding niche in the CaV1 channel, which is partially overlapping but distinct from blocking agents, but no one has yet determined the precise molecular basis of modal switching. One would think that, in the period of time between 1984 and today—some 30 years—that someone would have clarified this at the molecular level. But no one has. What we do know is that G protein subunits and protein phosphorylation are powerful regulators.

Transitioning from Heart to Brain via Calcium Channel Types

Did you always have in the back of your mind that you’d get to neuroscience, having fallen in love with it on the basis of your friend [Robert Macdonald]’s lobbying? Or did you just happen to find a problem you were interested in and make the shift? (Adler, 2015)

I stayed interested in the brain, and in learning and memory, throughout my career. For example, just before my doctoral submission, I wrote an essay about the importance of understanding vision and the role of molecular biology in deciphering it. Entitled “Biological Variations on Themes by Descartes,” and published as part of a multi-authored tribute to Maurice Bowra, the pop piece was inspired by Descartes’ diagram featured in a fascinating lecture by Colin Blakemore. The essay had both merit and flaws, but it provides an early pointer to my long-term interest in neuroscience. Although my Yale lab’s work on the cell biology of excitable cells bore general relevance to brain cells, our experimental efforts on neurons would be delayed for some 15 years.

Elucidating Calcium Channel Diversity

The advent of patch clamp recordings swept away concerns about the authenticity of Ca2+ channels and lowered energy barriers for switching cell types. Martha Nowycky, who had worked on adrenergic modulation of L-type channels with Bruce Bean (Bean et al., 1984), began patch-clamping dorsal root ganglion neurons with Aaron Fox. Martha came from the Neuroanatomy Department at Yale and had a broader neurobiological perspective than the rest of us. Before joining my lab to work on vertebrate cells, Aaron Fox had been mentored by Sally Krasne and Susumu Hagiwara and had studied calcium channels in invertebrate eggs. Ed McCleskey, already mentioned, had worked on the biophysics of calcium channels in skeletal muscle with Wolfhard Almers. We started off expecting that these sensory neurons wouldn’t be that much different than the heart cells we were studying in another corner of the lab. Our guinea pig heart cells displayed unitary currents of T- and L-type channels (Nilius et al., 1985), much as expected from Bean’s own whole-cell recordings (Bean, 1985) and earlier reports from other cell types from Hagiwara, Lux, Carbone, and Armstrong (Armstrong and Matteson, 1985; Carbone and Lux, 1984; Hagiwara et al., 1975; Matteson and Armstrong, 1986). The voltage dependence of T-type channels had been anticipated by Llinás (Llinás and Yarom, 1981) and made them easy to pick out. But Martha noticed patterns of channel opening that couldn’t be reconciled with just two distinguishable types of calcium channels. The hardest part was to separate what would later prove to be L-type (CaV1) and N-type (CaV2) channels. Fortunately, pharmacology helped us (Nowycky et al., 1985a). We already knew of the aforementioned 1,4-dihydropyridine derivative, Bay K 8644, that dramatically increased the openness of L-type channels in the heart (Hess et al., 1984). Bay K 8644 acted selectively on the L-type channels in neurons, sparing the maverick N-type openings. Our designation “N-type” stood for neuron-specific and neither of the other two types, that is, T-type or L-type channels (Nowycky et al., 1985b). What made this discovery interesting is the fact that we found a type of calcium channel that seemed to be neuron specific (Tsien et al., 1987), raising the possibility that it might play some kind of special role.

Marine Conesnails and Neurotransmitter Release

Then, almost like a deus ex machina, a newly discovered form of toxin, omega-conotoxin GVIA, came on the scene thanks to pioneering work of Baldomero (“Toto”) Olivera and Doju Yoshikami. Back then, the toxin wasn’t known as “GVIA” but simply as omega-conotoxin. Toto and Doj joined us in collaboration led by Ed McCleskey, Aaron Fox, and Dan Feldman, showing that the toxin blocked the N-type channel (McCleskey et al., 1987). In so doing, GVIA blocked transmitter release from sympathetic neurons, which we showed in further collaboration with Richard Miller’s group (Hirning et al., 1988). Our lab was fortunate in many respects, particularly in having a small but excellent group of scientists, all willing to follow the gradient of the most interesting biology. Our collaborations with other labs were quickly set up, neatly combined everyone’s expertise, and led to brief papers with a straightforward conclusion. As a result, between 1985 and 1989, we not only were able to describe a new type of calcium channel but also to show its role in transmitter release. And just as the discovery of N-type channels led to our interest in synaptic transmission, synaptic transmission led us to synaptic plasticity and an interest in learning and memory. So, within the space of five years, we had gone from being a cardiac electrophysiology lab to a lab that was working on LTP.

Robert Malinow, Daniel Madison, and I began studying LTP while we were still at Yale, and carried on full force after changing institutions together in 1988 (Malinow et al., 1988; Malinow et al., 1989). Our interest was in the involvement of protein kinases in the synaptic strengthening, and for one paper, we teamed up with Howard Schulman. Our work anticipated future studies of how calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) each contribute to induction and maintenance of LTP. Synaptic plasticity is an ongoing area of activity in our lab that I will review elsewhere.

Another memorable set of Yale-based interactions took place in 1987, at a membrane course at the Institute of Physiology in Shanghai, headed by the famous Chinese neuroscientist T. P. Feng (Tsien, 2007). Feng had made fundamental contributions to understanding activation in muscle and nerve and was a fascinating link between A. V. Hill’s lab in the United Kingdom and China. My scientific grandfather Otto Hutter was the convener of the course, and Peter Hess, Diane Lipscombe, Bernd Nilius, Fred Sigworth, Li-Yen Mae Huang, Victor Pantani, and I were the instructors. To help establish single-cell and single-channel recording methods in China, we brought the patch clamp amplifiers and computers for data acquisition with us, and then donated the computers. As someone born in China, it was satisfying to have contributed to the upswing of biophysics and neuroscience in the home of my ancestors (Tsien, 2007).

Amazing Mentors at Yale

Rick Aldrich and David Clapham have given informal interviews about the atmosphere at Yale and the membrane biophysics that was done there. For example, Fred Sigworth pioneered both early analysis of electrical single-channel recordings and modern-day structural analysis of single-channel particles visualized by cryo-electron microscopy (cryo-EM). For my part, I would like to express my appreciation for four exceptional neuroscientists who I looked up to and learned from.

Knox Chandler, one of the brightest scientists I have ever met, was as quick with a biting quip as he was thorough and slow in writing up papers. His amazingly careful papers with Meves actually began as a rebuttal of Ichiji Tasaki, at Alan Hodgkin’s request. I greatly admired Chandler’s experiments with Martin Schneider on membrane charge movements as a key step in E-C coupling (Schneider and Chandler, 1973), a partial answer to my rose garden queries of Hodgkin. Knox’s personality dominated seminars and long lunches within the Physiology Department. He and his wife Caroline were generous in providing friendship, hospitality, and sage advice to me, Rocky Kass, William Gilly, and others.

Chuck Stevens was recruited from the University of Washington, Seattle, soon after I arrived at Yale. Later, he headed up a Section of Molecular Neurobiology, where he assembled a dazzling cast of scientists, including several future National Academy Members. Chuck is a highly accomplished mentor and talent-spotter, but like Knox Chandler, Bertil Hille, Clay Armstrong, George Eisenman, and other brilliant exemplars of their generation, Chuck had an aversion to full-blown administration. This gave me pause when I had such choices to make about starting new academic entities at Stanford and NYU.

Larry Cohen was an early prototype of a tool-builder, much more fashionable now than when he began his pioneering work on voltage-sensitive dyes. He gave us an underappreciated glimpse of the ensemble recordings that pervade modern systems neuroscience, and stood up against overly simplistic views. While we were mutually supportive friends, Larry Cohen often teased me about my ethnic origins with politically incorrect, albeit affectionately delivered epithets, evocatively recounted in a whole chapter about Larry (Nicholls, 2015).

J. Murdoch Ritchie was the chair of the Pharmacology Department, a sister department to the Physiology Department that saw Gerhard Giebisch and Joseph Hoffman as chair. Murdoch had worked with R. D. Keynes and appreciated the importance of getting at the molecular underpinnings of excitability. He provided a role model of someone who was very good at experiments but willing to do administration for the benefit of others. He gave me great advice about an authorship conflict and told me not to let my review articles be boringly middle of the road.

Why It Wasn’t So Hard to Leave Yale

Robert Berliner, dean of Yale Medical School and a member of the Physiology Department, always appeared dressed in a tweed jacket that smelled of the pipe he smoked. He once told me casually that the chairmanship of the Department of Physiology was preordained to go to Walter Boron as an extension of the Yale kidney dynasty. Berliner had worked on the kidney and Gerhard Giebisch (my first chair) and Emile Boulpaep (the current chair) were renal physiologists, so Walter was a logical choice. At the time, I wouldn’t have been eager to serve as chair of such a top-heavy department, and I respected Walter Boron, his diligence, fairness, and contributions to science. Nonetheless, Berliner’s dismissal of anyone but Walter, simply on grounds of field, took me aback. Likewise, George Palade, whose name graces a prize I later won, seemed surprised and instantly dismissive of my inquiring about the future prospects of an endowed chair. The lesson was that a scientist’s stock in their home institution often lags behind their market value elsewhere (creating perennial challenges for institutional leadership, something I now feel acutely).

Back then, some leading competitors of Yale seemed to hold a much higher opinion of our work. For example, Daniel Tosteson at Harvard and Daniel Nathans at Johns Hopkins were highly respected leaders who tried with their own special charisma to recruit me to Boston and Baltimore, respectively. Julia, the alpha dog of our family, was open to Harvard but adamantly against Baltimore (its downtown had the same problems as New Haven, and she was opposed to living in the suburbs). For once, the “spousal excuse” was true, as I quickly informed Dan Nathans; within weeks, they approached my brother Roger Tsien, but he also eventually said no. In the end, I passed up three excellent opportunities to take up positions that came bundled with an investigatorship with the Howard Hughes Medical Institute (HHMI), including one linked with a retention offer at Yale. The then-dean Leon Rosenberg worked hard to keep both Chuck Stevens and me from exiting Yale, but in the end, we both left. For me, the allure of starting a new department at Stanford was too much, regardless of passing up an HHMI appointment, which was then prohibited for scientists serving as a departmental chair. I wound up interacting closely with Max Cowan, the head of HHMI, on Stanford’s HHMI appointments and have since served on many HHMI bodies, including the Scientific Review Board, the Medical Advisory Board, and Janelia Farm Advisory Board.

Starting a Department from Scratch at Stanford

In 1988, I accepted a position at Stanford University to create a new entity, the Department of Molecular and Cellular Physiology (MCP). Stanford medical school’s department of physiology had one remaining faculty member, a reproductive physiologist near retirement. The head of the search committee, James Spudich, a pioneer in the field of cell motility, asked me for informal input, and I gave them so much advice that they simply offered me the position. At 43, I had no real administrative experience but relished the challenge of starting a new department from the ground up.

In hindsight, our new department was probably a bit of an afterthought. Under the leadership of Nobel laureate Paul Berg, the launching of the Beckman Center was well underway, composed of Stanford’s famous Department of Biochemistry on the fourth floor, a new Department of Developmental Biology, a spinoff of biochemistry, headed by Lucille Shapiro on the third floor, and an HHMI unit featuring investigators like Mark Davis and Gerald Crabtree on the second floor. Adding MCP on the ground floor allowed Stanford to fulfill teaching obligations and to link physiology and medicine, developmental biology, and molecular biology. Although “physiology” implied old-school organ studies, inserting “molecular and cellular” as a prefix seemed to capture something fresh. Thus, Stanford was ready to gamble the grand sum of $3 million to bankroll the new department. Fortunately, the New York–based Mathers Charitable Foundation provided start-up funds, beginning a close relationship that continues to this day. Max Cowan of HHMI had agreed to support two faculty members directly, and another HHMI position would become available through collaboration with the Stanford’s Department of Medicine. Spudich and Eric Shooter, then chair of the Department of Neurobiology would join with Libby Kirk-Fulton, an administrative power in biochemistry, to save the naive chairperson from too many novice mistakes.

One of Kirk-Fulton’s first moves was to steer me sternly to hire an experienced business manager, Shayne Frankel, who came over from Stanford’s Medical Microbiology Department. Shayne enjoyed the challenge of starting a new department in a brand-new building with an inexperienced chair. MCP was clearly the youngest sib, the runt of the litter, with none of the tradition of Shooter’s Department of Neurobiology, an heir to both the excellence and somewhat insular outlook of Kuffler’s famous department at Harvard. But our department benefited from the backing of then-Dean David Korn, a gruff and outwardly cynical mover and shaker, who always gave me the feeling that he had our backs as academic underdogs.

What no one really expected was that the growth of my personal interest in neuroscience, fresh resources, and influx of energetic young people would combine to make MCP a hotbed of molecular neuroscience and cell biology. Our able colleagues in the Neurobiology Department may not have been prepared for an MCP Department with so many neuroscientists in it. But that’s what Daniel Madison, Thomas Schwarz, Stephen Smith, and Richard Lewis were. HHMI investigatorships supported Richard Aldrich and Richard Scheller, both already at Stanford, in adding their strengths to the nascent group. The current chairperson, Miriam Goodman, came to Stanford from Columbia University, and studies touch sensation all the way from sensory ion channels to brain signals. Neuroscience thrived in a healthy mix with studies of the physiology and cell biology of nonexcitable cells. For example, Brian Kobilka took up a junior HHMI position under the aegis of Stanford’s Department of Medicine to work on adrenergic receptor signaling. James Nelson, a cell biologist and leader in studies of how epithelial polarization develops and is maintained, came from a cancer institute near Philadelphia. Richard Lewis clarified mechanisms for calcium entry and gene activation in immune cells, building on his previous work studying cochlear hair cells. Like Rick Aldrich and Miriam Goodman, all three of these scientists later served as rotating chair of MCP, combining their excellent science with institutional service. Later, we would be joined by Merritt Maduke, a channel biophysicist, and William Weis, Axel Brunger, and Christopher Garcia, all remarkable structural/cell biologists. Although MCP had neuroscience as one of its foci, everyone felt open to explorations of non-neuro areas. Perhaps I am forgetting, but there weren’t the kind of territorial conflicts over areas of recruitment that I had seen at Yale.

Over the years, we developed a warm sense of family and accomplished remarkable things while mentoring outstanding trainees (Karl Deisseroth, Edward Boyden, Richard Mooney, Erin Schuman, and Timothy Ryan come to mind as representative examples). Investigators and their lab members interacted in the halls, in seminars, and at annual retreats at or near Asilomar. There was room for silly congeniality. Our lab won two Asilomar Halloween contests for best costume, one a headdress for disco partying made of discarded computer parts such as floppy disks (remember them?), another a Snow White costume that Rachel Groth coaxed me to wear while the lab came as the Seven Dwarfs (thankfully, no photographic evidence survives). Amidst the jollity, we had scientific sessions as high in quality as any symposium at the Society for Neuroscience (SfN) or the American Society of Cell Biology (ASCB).

Return on Investment

I look back with satisfaction on accolades MCP garnered after I left in 2011. Currently, three of the faculty members in this little department are Nobel Laureates. Brian Kobilka was awarded the 2012 Nobel Prize in Chemistry for determining the first structure of a G protein coupled receptor, something he had wanted to do ever since his recruitment from a Duke postdoc with co-winner Robert Lefkowitz in 1989. Thomas Südhof, honored in Stockholm for his work on synaptotagmin and calcium-triggered secretion, has spoken eloquently about how “Science happens in the interaction between people. . . . It’s not an activity carried out by an isolated individual.” Steven Chu brought unusual perspective as both a Nobel Prize–winning physicist and a former energy secretary and has now turned to biological problems. With these and other awards (e.g., a Lasker for Richard Scheller), MCP gave Stanford a pretty good return on its $3 million investment. Our faculty learned many lessons at Stanford: how to foster interactions, and how to help people do things they can take pride in and get credit for. I greatly appreciate the confidence that Stanford showed in allowing us to build a department from the ground up. Equally important were the individuals who supported the department, particularly Shayne Frankel, Elizabeth Lasensky, Cathy Booth, David Profitt, Elisabeth Einaudi, and other folks who led or served on our excellent staff.

Studies of Calcium Channel Diversity, Function, and Neuromodulation

By the early 1990s, our appreciation of distinctions among multiple calcium channel types had been extended by molecular cloning, thanks to Shosaku Numa at Kyoto and Terry Snutch with Norm Davidson and Henry Lester at Caltech and later at the University of British Columbia. The channel subfamily exemplified by N-type channels, now known as CaV2 channels, consisted of three different pore-forming subunits, encoded by three distinct genes. A thorough and up-to-date summary can be found in a supplemental figure of a recent Nature paper on the 3D structure of a T-type channel (Zhao et al., 2019). We failed to isolate the N-type channel cDNA, an honor earned by Terry Snutch’s group (Dubel et al., 1992); however, we succeeded with Bill Horne and Tom Schwarz in cloning the first exemplar of CaV2.3 channels (Ellinor et al., 1993). We also collaborated with Shosaku Numa’s lab in studying the channels encoded by CaV2.1 (Sather et al., 1993). Just as collaboration with Olivera and Yoshikami broke new ground in pharmacological dissection of N-type Ca2+ channels (CaV2.2 in modern terminology) (McCleskey et al., 1987), partnership with Michael Adams at the University of California, Riverside, established that what we called P- and Q-type channels (both CaV2.1 gene products) were very differently inhibited by ω-AgaToxin IVA (Jun et al., 1999; Sather et al., 1993). Likewise, in a collaboration with George Miljanich and colleagues at Neurex, we showed that a peptide venom SNX-482 was a potent inhibitor of R-type (CaV2.3) channels (Newcomb et al., 1998). Thus, following the collaboration with Olivera and Yoshikami, specific toxin blockers for individual subtypes of the maverick family of calcium channels became available within little more than a decade.

Like Tomiyuki Takahashi (Takahashi and Momiyama, 1993) and Kathleen Dunlap (Luebke et al., 1993), our lab was also interested in studying the roles of the CaV2 channels in synaptic transmission. David Wheeler and Andy Randall showed that N-, P/Q-, and R-type channels all contribute to synaptic transmission at archetypical brain synapses (Wheeler et al., 1994) and cooperate even at the level of individual synapses (Wheeler et al., 1996). Today, the standard procedure for dissecting Ca2+ channels that support transmitter release is to use ω-conotoxin GVIA (N-type), ω-AgaToxin IVA (P/Q-type), and SNX-482 (R-type), each an agent we helped put on the map.

Interest in LTP

The early 1990s saw intense interest in LTP as a putative basis for learning and memory. Roger Nicoll has given an evocative account of the development of ideas in this era (Nicoll, 2017). Here I will stick to dry facts and be brief, saving a more detailed and data-oriented treatment for another occasion. Robert Malinow and I performed quantal analysis (Malinow and Tsien, 1990) that was subsequently replicated by other groups (Larkman et al., 1992; Stricker et al., 1996). Because we saw consistent changes in quantal amplitude, we never interpreted the results as purely presynaptic. However, one hint of genuine presynaptic involvement was potentiation of NMDAR-mediated transmission (Malgaroli et al., 1992; Tsien and Malinow, 1990), a finding also reported by others (Bashir et al., 1991). Aware of the interpretational ambiguity of quantal analysis, we sought more direct ways of establishing a bona fide presynaptic change, switching to hippocampal cultures, and found compelling evidence for presynaptic modifications following NMDAR-mediated LTP (Malgaroli et al., 1995; Malgaroli and Tsien, 1992). This work was also later replicated and extended to show roles of PKA, nitric oxide, and cyclic GMP-dependent protein kinase (Antonov et al., 2003; Arancio et al., 1995; Wang et al., 2005). Recent work with Nicolas Chenouard traces the underlying mechanism to a redistribution of presynaptic resources through actin-dependent transport of synaptic vesicles along the axon.

Advancing Cell Biological Approaches to Neurotransmission

Debate about the locus of expression of LTP had one additional benefit: focusing attention on the cell biology of presynaptic terminals. The activity-dependent uptake of a vesicle-staining dye, FM1-43 (Betz et al., 1992; Betz et al., 1996) facilitated studies of hippocampal synapses (Murthy et al., 1997; Ryan et al., 1993). We studied quantal events at visually identified single synapses and showed that AMPA receptors were far from saturated (Liu and Tsien, 1995), in agreement with work from the Stevens lab (McAllister and Stevens, 2000). Later, we used brightly fluorescent quantum dots to track the functional status and location of single synaptic vesicles (Park et al., 2012; Zhang et al., 2007; Zhang et al., 2009). Debate about the fate of once-fused vesicles and an intriguing mechanism known as kiss-and-run goes on (Alabi and Tsien, 2013), and warrants further review of fresh data, including direct visualization of kiss-and-run events in non-neuronal systems (Eyring and Tsien, 2018; Shin et al., 2018).

Activity-Dependent Gene Expression

In the mid-1990s, two remarkable researchers in our lab, Karl Deisseroth and Haruhiko Bito, instigated studies of how neuronal activity controls transcription, later joined by other excellent members of our lab, such as Paul Mermelstein. Excitation-transcription coupling remains a topic of interest in our lab, and the great work of trainees like Damian Wheeler, Rachel Groth, Huan Ma, Samuel Cohen, Boxing Li, and Michael Tadross deserves reviews of its own. My colleagues and I have never discussed it, but I hope that they will take pleasure in the historical resonance between my rose garden talk with Alan Hodgkin about E-C coupling, and our later work together on E-T coupling and excitation-alternative splice (E-AS) coupling. It is exciting to have identified a novel mechanism for signal transmission, involving translocation of CaM complexed with γCaMKII (Ma et al., 2014) and to have shown a critical role of such translocation for behavioral memory (Cohen et al., 2018).

Willingness to Leave Stanford

To this day, I sometimes meet people like Dutch systems neuroscientist, a fan of Bill Newsome, who was incredulous that anyone would voluntarily move away from Stanford. Indeed, Stanford’s high-quality faculty are remarkable as are its facilities and campus complete with horse farm, botanical garden, golf course, and shopping center. This campus harbored an architecturally distinctive house where Julia and I raised our three children. Sarah, Greg, and Alexa each took a eucalyptus-lined path to an excellent public elementary school that Bill Newsome’s sons also attended and contributed to life in a high school with features of Scarborough, Livingston High, and Bronx Science rolled up into one. It was bucolically beautiful, safe, and a terrific place to raise a family. But after more than two decades at Stanford, in many ways a company town, Julia was keen to move to San Francisco. Grateful for our Stanford experience, we were also open-minded about leaving it behind.

Berkeley as an Intriguing Opportunity

I was given attractive offers at both University of California, Berkeley, and NYU to spearhead the building up of neuroscience. The recruitment at Berkeley was led by Muming Poo and Robert Tjian, two highly respected scientists with well-known leadership talents, and driven by John Ngai. As a public university with a tradition of excellence, Berkeley tapped into my altruistic side and offered my family a chance to continue its California lifestyle. I very much liked the people and spirit at Berkeley but then practicalities set in. The then-chancellor spent much of our interview dreading his very next appointment—to announce the elimination of Berkeley’s baseball team. Further highlighting Berkeley’s resource shortage, the then-dean offered about $13 million to strengthen neuroscience but stipulated payback of almost all of this money before any new philanthropy could be routed to Berkeley neuroscience.

NYU Offers the Chance to Join a Medical Center on the Rise

In 2011, Julia and I moved from Stanford to NYU, where I head up a new Neuroscience Institute at the NYU Langone (now NYU Grossman) School of Medicine. I also lead a distinguished department of neuroscience and physiology, formerly chaired by Rodolfo Llinás, and mentor a group of amazing faculty, both within the Institute and department and outside it. The Neuroscience Institute was launched with a $100 million gift from Fiona and Stanley Druckenmiller, two generous and farseeing philanthropists, close friends of Kenneth Langone and admirers of Robert Grossman, who have led NYU’s upswing in recent years. Although the Druckenmillers aimed to support fundamental research in neuroscience, with no strings attached, our Institute has built on their unspoken intentions and endeavored to make connections with research-oriented clinicians. For example, Gyuri Buzsáki (my most senior recruit) and I both enjoy our close collaborations with Orrin Devinsky, head of the Epilepsy Center. We work together on a U19 project with Robert Froemke and Dayu Lin, exemplars of the excellent faculty at NYU in studying oxytocin, currently in clinical trials to test its possible therapeutic benefit. We received generous funding from Paolo Fresco to work on Parkinson’s. Our core faculty are often cross-appointed in clinical departments and regularly help with recruitment, retention, and mentoring.

Community and Education

I have spoken about NYU elsewhere (Haseltine, 2019) and regard it as a demanding yet fulfilling adventure worth an essay on its own. Briefly, my colleagues and I are hopeful of achieving two major goals. First, to bring molecular and cellular neuroscience and systems neuroscience closer together. Second, to strike the right balance between exclusivity and inclusion. Some leaders invoke an elitist spirit to create a tight-knit community: Kuffler’s Neurobiology Department was a prime example (McMahan and Katz, 1990). In building the NYU Neuroscience Institute, my co-founder Gord Fishell and I strove for excellence but had a far more inclusive community in mind. Our seminar series, weekly progress reports and annual retreat are all open to the wider community of neuroscientists at NYU, including med school researchers not housed in our new science building as well as members of the Center for Neural Science (CNS) started by Tony Movshon at NYU’s main campus at Washington Square, two miles downtown. We join with our CNS colleagues to co-administer a graduate program that draws excellent students.

Coda

I am sending off this piece on January 5, 2020, which happens to be the birthday of Julia Shiang, who remains the light of my existence, full of surprises, the joy of life, and more than a few strong opinions. The year 2020 will be the 50th anniversary of my halting attempts to start up my own lab with help from wonderfully supportive senior faculty, wise chairperson, and risk-tolerant trainees. Stories about my Chinese immigrant background, schooling, friends, and outstanding early mentors help explain the curiosity that has driven my lab and the mix of idealism and pragmatism that has fueled my department-building. Each of my institutional transitions, spaced about 20 years apart, enabled a new tack: filling a vacated position at Yale replaced organ physiology with cell biology and signaling and enabled a transition to neuroscience; reviving a moribund department of physiology at Stanford advanced molecular neuroscience and cell biology; starting an institute at NYU now fosters closer ties between cellular and systems neuroscience. It has been my privilege to study how membrane excitation triggers diverse cellular responses such as contraction, secretion, transcription, and now alternative splicing, as presaged by the Oxford rose garden conversation so long ago. Calcium channels held our attention as both biophysical marvels and elegant signal transducers, performing more vital functions than a Swiss army knife. I am lucky to be a memory-laden link between the excitability studies of my scientific forbears and the optogenetics of some renowned scientific descendants. I thank the colleagues, trainees, and friends—many who I didn’t have space to mention individually but are listed in the attached table—who worked so hard and so well to make this journey meaningful for my scientific family.

Coda on Coda

I’m very grateful to Thomas Albright for his superb editing, and both Tom and Larry Squire for this opportunity. As I submit a near-final version, it’s mid-April, partway through the 2020 spring of COVID-19. We face enormous medical, economic, and political challenges; NYC is an epicenter of the outbreak and China is a target of criticism, pertinent to this story. Perhaps recalling past decades will hearten us and remind us of useful roles we can carry out as part of society at large.

References

Adler, E.M. (2015). A well-channeled journey from heart to brain: An interview with Dick Tsien. Sounds Physiological (28 min). https://www.stitcher.com/podcast/the-rockefeller-university-press-2/sounds-physiological/e/a-wellchanneled-journey-from-heart-to-brain-dick-tsien-40638879

Adrian, R.H., Chandler, W.K., and Hodgkin, A.L. (1969). The kinetics of mechanical activation in frog muscle. J Physiol 204, 207–230.

Adrian, R.H., Chandler, W.K., and Hodgkin, A.L. (1970a). Slow changes in potassium permeability in skeletal muscle. J Physiol 208, 645–668.

Adrian, R.H., Chandler, W.K., and Hodgkin, A.L. (1970b). Voltage clamp experiments in striated muscle fibres. J Physiol 208, 607–644.

Alabi, A.A., and Tsien, R.W. (2013). Perspectives on kiss-and-run: role in exocytosis, endocytosis, and neurotransmission. Annu Rev Physiol 75, 393–422.

Almers, W., and McCleskey, E.W. (1984). Non-selective conductance in calcium channels of frog muscle: calcium selectivity in a single-file pore. J Physiol 353, 585–608.

Antonov, I., Antonova, I., Kandel, E.R., and Hawkins, R.D. (2003). Activity-dependent presynaptic facilitation and hebbian LTP are both required and interact during classical conditioning in aplysia. Neuron 37, 135–147.

Arancio, O., Kandel, E.R., and Hawkins, R.D. (1995). Activity-dependent long-term enhancement of transmitter release by presynaptic 3’,5’-cyclic GMP in cultured hippocampal neurons. Nature 376, 74–80.

Armstrong, C.M., and Matteson, D.R. (1985). Two distinct populations of calcium channels in a clonal line of pituitary cells. Science 227, 65–67.

Armstrong, C.M., and Neyton, J. (1991). Ion permeation through calcium channels. A one-site model. Ann N Y Acad Sci 635, 18–25.

Baker, P.F., Hodgkin, A.L., and Meves, H. (1964). The Effect of Diluting the Internal Solution on the Electrical Properties of a Perfused Giant Axon. J Physiol 170, 541–560.

Baker, P.F., Hodgkin, A.L., and Shaw, T.I. (1961). Replacement of the protoplasm of a giant nerve fibre with artificial solutions. Nature 190, 885–887.

Bashir, Z.I., Alford, S., Davies, S.N., Randall, A.D., and Collingridge, G.L. (1991). Long-term potentiation of NMDA receptor-mediated synaptic transmission in the hippocampus. Nature 349, 156–158.

Bean, B.P. (1985). Two kinds of calcium channels in canine atrial cells. Differences in kinetics, selectivity, and pharmacology. J Gen Physiol 86, 1–30.

Bean, B.P., Cohen, C.J., and Tsien, R.W. (1983). Lidocaine block of cardiac sodium channels. J Gen Physiol 81, 613–642.

Bean, B.P., Nowycky, M.C., and Tsien, R.W. (1984). Beta-adrenergic modulation of calcium channels in frog ventricular heart cells. Nature 307, 371–375.

Betz, W.J., Mao, F., and Bewick, G.S. (1992). Activity-dependent fluorescent staining and destaining of living vertebrate motor nerve terminals. J Neurosci 12, 363–375.

Betz, W.J., Mao, F., and Smith, C.B. (1996). Imaging exocytosis and endocytosis. Curr Opin Neurobiol 6, 365–371.

Boyd, I.A., and Martin, A.R. (1956). The end-plate potential in mammalian muscle. J Physiol 132, 74–91.

Boyden, E.S., Zhang, F., Bamberg, E., Nagel, G., and Deisseroth, K. (2005). Millisecond-timescale, genetically targeted optical control of neural activity. Nat Neurosci 8, 1263–1268.

Buzsáki, G. (2011). Rhythms of the brain (Oxford; New York: Oxford University Press).

Carbone, E., and Lux, H.D. (1984). A low voltage-activated, fully inactivating Ca channel in vertebrate sensory neurones. Nature 310, 501–502.

Cataldi, M., Perez-Reyes, E., and Tsien, R.W. (2002). Differences in apparent pore sizes of low and high voltage-activated Ca2+ channels. J Biol Chem 277, 45969–45976.

Chandler, W.K., Hodgkin, A.L., and Meves, H. (1965). The effect of changing the internal solution on sodium inactivation and related phenomena in giant axons. J Physiol 180, 821–836.

Chang, I. (2008). Thread of the silkworm (New York: Basic Book).

Chen, X.H., Bezprozvanny, I., and Tsien, R.W. (1996). Molecular basis of proton block of L-type Ca2+ channels. J Gen Physiol 108, 363–374.

Chen, X.H., and Tsien, R.W. (1997). Aspartate substitutions establish the concerted action of P-region glutamates in repeats I and III in forming the protonation site of L-type Ca2+ channels. J Biol Chem 272, 30002–30008.

Chiamvimonvat, N., Chen-Izu, Y., Clancy, C.E., Deschenes, I., Dobrev, D., Heijman, J., Izu, L., Qu, Z., Ripplinger, C.M., Vandenberg, J.I., et al. (2017). Potassium currents in the heart: functional roles in repolarization, arrhythmia and therapeutics. J Physiol 595, 2229–2252.

Cohen, L.B., Keynes, R.D., and Hille, B. (1968). Light scattering and birefringence changes during nerve activity. Nature 218, 438–441.

Cohen, S.M., Suutari, B., He, X., Wang, Y., Sanchez, S., Tirko, N.N., Mandelberg, N.J., Mullins, C., Zhou, G., Wang, S., et al. (2018). Calmodulin shuttling mediates cytonuclear signaling to trigger experience-dependent transcription and memory. Nat Commun 9, 2451.

Colatsky, T.J., and Tsien, R.W. (1979). Electrical properties associated with wide intercellular clefts in rabbit Purkinje fibres. J Physiol 290, 227–252.

Dang, T.X., and McCleskey, E.W. (1998). Ion channel selectivity through stepwise changes in binding affinity. J Gen Physiol 111, 185–193.

Dawkins, R. (1989). The selfish gene (Oxford: Oxford University Press).

Dubel, S.J., Starr, T.V., Hell, J., Ahlijanian, M.K., Enyeart, J.J., Catterall, W.A., and Snutch, T.P. (1992). Molecular cloning of the alpha-1 subunit of an omega-conotoxin-sensitive calcium channel. Proc Natl Acad Sci USA 89, 5058–5062.

Ellinor, P.T., Yang, J., Sather, W.A., Zhang, J.F., and Tsien, R.W. (1995). Ca2+ channel selectivity at a single locus for high-affinity Ca2+ interactions. Neuron 15, 1121–1132.

Ellinor, P.T., Zhang, J.F., Randall, A.D., Zhou, M., Schwarz, T.L., Tsien, R.W., and Horne, W.A. (1993). Functional expression of a rapidly inactivating neuronal calcium channel. Nature 363, 455–458.

Eyring, K.W., and Tsien, R.W. (2018). Direct visualization of wide fusion-fission pores and their highly varied dynamics. Cell 173, 819–821.

Giebisch, G., and Weidmann, S. (1971). Membrane currents in mammalian ventricular heart muscle fibers using a voltage-clamp technique. J Gen Physiol 57, 290–296.

Hagiwara, S., and Byerly, L. (1981). Calcium channel. Annu Rev Neurosci 4, 69–125.

Hagiwara, S., Ozawa, S., and Sand, O. (1975). Voltage clamp analysis of two inward current mechanisms in the egg cell membrane of a starfish. J Gen Physiol 65, 617–644.

Hamill, O.P., Marty, A., Neher, E., Sakmann, B., and Sigworth, F.J. (1981). Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflugers Arch 391, 85–100.

Haseltine, W.A. (2019). World class: a story of adversity, transformation, and success at NYU Langone Health (Austin: Greenleaf Book Group).

Hauswirth, O., Noble, D., and Tsien, R.W. (1968). Adrenaline: mechanism of action on the pacemaker potential in cardiac Purkinje fibers. Science 162, 916–917.

Hauswirth, O., Noble, D., and Tsien, R.W. (1969). The mechanism of oscillatory activity at low membrane potentials in cardiac Purkinje fibres. J Physiol 200, 255–265.

Hess, P., Lansman, J.B., and Tsien, R.W. (1984). Different modes of Ca channel gating behaviour favoured by dihydropyridine Ca agonists and antagonists. Nature 311, 538–544.

Hess, P., and Tsien, R.W. (1984). Mechanism of ion permeation through calcium channels. Nature 309, 453–456.

Hirning, L.D., Fox, A.P., McCleskey, E.W., Olivera, B.M., Thayer, S.A., Miller, R.J., and Tsien, R.W. (1988). Dominant role of N-type Ca2+ channels in evoked release of norepinephrine from sympathetic neurons. Science 239, 57–61.

Hodgkin, A.L. (1976). Chance and design in electrophysiology: an informal account of certain experiments on nerve carried out between 1934 and 1952. J Physiol 263, 1–21.

Hodgkin, A.L., and Horowicz, P. (1960). Potassium contractures in single muscle fibres. J Physiol 153, 386–403.

Hodgkin, A.L., Huxley, A.F., and Katz, B. (1952). Measurement of current-voltage relations in the membrane of the giant axon of Loligo. J Physiol 116, 424–448.

Hutter, O.F., and Trautwein, W. (1956). Vagal and sympathetic effects on the pacemaker fibers in the sinus venosus of the heart. J Gen Physiol 39, 715–733.

Huxley, A.F., and Simmons, R.M. (1971). Proposed mechanism of force generation in striated muscle. Nature 233, 533–538.

Huxley, A.F., and Taylor, R.E. (1958). Local activation of striated muscle fibres. J Physiol 144, 426–441.

Jack, J., Noble, D., and Tsien, R.W. (1973). Electric current flow in excitable cells (Oxford: Clarendon).

Jack, J.J., Miller, S., Porter, R., and Redman, S.J. (1971). The time course of minimal excitory post-synaptic potentials evoked in spinal motoneurones by group Ia afferent fibres. J Physiol 215, 353–380.

Jack, J.J., and Redman, S.J. (1971a). An electrical description of the motoneurone, and its application to the analysis of synaptic potentials. J Physiol 215, 321–352.

Jack, J.J., and Redman, S.J. (1971b). The propagation of transient potentials in some linear cable structures. J Physiol 215, 283–320.

Johnson, E.A., and Lieberman, M. (1971). Heart: excitation and contraction. Annu Rev Physiol 33, 479–532.

Jun, K., Piedras-Renteria, E.S., Smith, S.M., Wheeler, D.B., Lee, S.B., Lee, T.G., Chin, H., Adams, M.E., Scheller, R.H., Tsien, R.W., et al. (1999). Ablation of P/Q-type Ca(2+) channel currents, altered synaptic transmission, and progressive ataxia in mice lacking the alpha(1A)-subunit. Proc Natl Acad Sci USA 96, 15245–15250.

Kass, R.S., Siegelbaum, S.A., and Tsien, R.W. (1979). Three-micro-electrode voltage clamp experiments in calf cardiac Purkinje fibres: is slow inward current adequately measured? J Physiol 290, 201–225.

Katz, B. (1967). Nerve, muscle, and synapse (New York; London: McGraw-Hill).

Katz, B., and Miledi, R. (1971). The effect of prolonged depolarization on synaptic transfer in the stellate ganglion of the squid. J Physiol 216, 503–512.

Kostyuk, P.G. (1981). Calcium channels in the neuronal membrane. Biochim Biophys Acta 650, 128–150.

Kuffler, S.W., and Hunt, C.C. (1952). The mammalian small-nerve fibers: a system for efferent nervous regulation of muscle spindle discharge. Res Publ Assoc Res Nerv Ment Dis 30, 24–47.

Kuo, C.C., and Hess, P. (1993). Characterization of the high-affinity Ca2+ binding sites in the L-type Ca2+ channel pore in rat phaeochromocytoma cells. J Physiol 466, 657–682.

Larkman, A., Hannay, T., Stratford, K., and Jack, J. (1992). Presynaptic release probability influences the locus of long-term potentiation. Nature 360, 70–73.

Lee, K.S., and Tsien, R.W. (1982). Reversal of current through calcium channels in dialysed single heart cells. Nature 297, 498–501.

Lee, K.S., and Tsien, R.W. (1983). Mechanism of calcium channel blockade by verapamil, D600, diltiazem and nitrendipine in single dialysed heart cells. Nature 302, 790–794.

Lepore, J. (2019). These truths: a history of the United States (New York: W. W. Norton).

Liu, G., and Tsien, R.W. (1995). Properties of synaptic transmission at single hippocampal synaptic boutons. Nature 375, 404–408.

Llinás, R., and Yarom, Y. (1981). Properties and distribution of ionic conductances generating electroresponsiveness of mammalian inferior olivary neurones in vitro. J Physiol 315, 569–584.

Luebke, J.I., Dunlap, K., and Turner, T.J. (1993). Multiple calcium channel types control glutamatergic synaptic transmission in the hippocampus. Neuron 11, 895–902.

Ma, H., Groth, R.D., Cohen, S.M., Emery, J.F., Li, B., Hoedt, E., Zhang, G., Neubert, T.A., and Tsien, R.W. (2014). gammaCaMKII Shuttles Ca(2+)/CaM to the Nucleus to Trigger CREB Phosphorylation and Gene Expression. Cell 159, 281–294.

Malgaroli, A., Malinow, R., Schulman, H., and Tsien, R.W. (1992). Persistent signalling and changes in presynaptic function in long-term potentiation. Ciba Found Symp 164, 176–191; discussion 192–176.

Malgaroli, A., Ting, A.E., Wendland, B., Bergamaschi, A., Villa, A., Tsien, R.W., and Scheller, R.H. (1995). Presynaptic component of long-term potentiation visualized at individual hippocampal synapses. Science 268, 1624–1628.

Malgaroli, A., and Tsien, R.W. (1992). Glutamate-induced long-term potentiation of the frequency of miniature synaptic currents in cultured hippocampal neurons. Nature 357, 134–139.

Malinow, R., Madison, D.V., and Tsien, R.W. (1988). Persistent protein kinase activity underlying long-term potentiation. Nature 335, 820–824.

Malinow, R., Schulman, H., and Tsien, R.W. (1989). Inhibition of postsynaptic PKC or CaMKII blocks induction but not expression of LTP. Science 245, 862–866.

Malinow, R., and Tsien, R.W. (1990). Presynaptic enhancement shown by whole-cell recordings of long-term potentiation in hippocampal slices. Nature 346, 177–180.

Matteson, D.R., and Armstrong, C.M. (1986). Properties of two types of calcium channels in clonal pituitary cells. J Gen Physiol 87, 161–182.

McAllister, A.K., and Stevens, C.F. (2000). Nonsaturation of AMPA and NMDA receptors at hippocampal synapses. Proc Natl Acad Sci USA 97, 6173–6178.

McCleskey, E.W., Fox, A.P., Feldman, D.H., Cruz, L.J., Olivera, B.M., Tsien, R.W., and Yoshikami, D. (1987). Omega-conotoxin: direct and persistent blockade of specific types of calcium channels in neurons but not muscle. Proc Natl Acad Sci USA 84, 4327–4331.

McMahan, U.J., and Katz, B. (1990). Steve: remembrances of Stephen W. Kuffler (Sunderland, MA: Sinauer Associates).

Murthy, V.N., Sejnowski, T.J., and Stevens, C.F. (1997). Heterogeneous release properties of visualized individual hippocampal synapses. Neuron 18, 599–612.

Neher, E., and Steinbach, J.H. (1978). Local anaesthetics transiently block currents through single acetylcholine-receptor channels. J Physiol 277, 153–176.

Nerbonne, J.M., and Kass, R.S. (2005). Molecular physiology of cardiac repolarization. Physiol Rev 85, 1205–1253.

Newcomb, R., Szoke, B., Palma, A., Wang, G., Chen, X., Hopkins, W., Cong, R., Miller, J., Urge, L., Tarczy-Hornoch, K., et al. (1998). Selective peptide antagonist of the class E calcium channel from the venom of the tarantula Hysterocrates gigas. Biochemistry 37, 15353–15362.

Nicholls, J.G. (2015). Pioneers of neurobiology: my brilliant eccentric heroes (Sunderland, MA: Sinauer Associates).

Nicoll, R.A. (2017). A brief history of long-term potentiation. Neuron 93, 281–290.

Nilius, B., Hess, P., Lansman, J.B., and Tsien, R.W. (1985). A novel type of cardiac calcium channel in ventricular cells. Nature 316, 443–446.

Noble, D. (1962). A modification of the Hodgkin—Huxley equations applicable to Purkinje fibre action and pace-maker potentials. J Physiol 160, 317–352.

Noble, D. (1966). Applications of Hodgkin-Huxley equations to excitable tissues. Physiol Rev 46, 1–50.

Noble, D. (2006). The music of life: biology beyond the genome (Oxford; New York: Oxford University Press).

Noble, D., and Tsien, R.W. (1968). The kinetics and rectifier properties of the slow potassium current in cardiac Purkinje fibres. J Physiol 195, 185–214.

Noble, D., and Tsien, R.W. (1969a). Outward membrane currents activated in the plateau range of potentials in cardiac Purkinje fibres. J Physiol 200, 205–231.

Noble, D., and Tsien, R.W. (1969b). Reconstruction of the repolarization process in cardiac Purkinje fibres based on voltage clamp measurements of membrane current. J Physiol 200, 233–254.

Nowycky, M.C., Fox, A.P., and Tsien, R.W. (1985a). Long-opening mode of gating of neuronal calcium channels and its promotion by the dihydropyridine calcium agonist Bay K 8644. Proc Natl Acad Sci USA 82, 2178–2182.

Nowycky, M.C., Fox, A.P., and Tsien, R.W. (1985b). Three types of neuronal calcium channel with different calcium agonist sensitivity. Nature 316, 440–443.

Park, H., Li, Y., and Tsien, R.W. (2012). Influence of synaptic vesicle position on release probability and exocytotic fusion mode. Science 335, 1362–1366.

Polster, A., Perni, S., Bichraoui, H., and Beam, K.G. (2015). Stac adaptor proteins regulate trafficking and function of muscle and neuronal L-type Ca2+ channels. Proc Natl Acad Sci USA 112, 602–606.

Rall, W., Burke, R.E., Holmes, W.R., Jack, J.J., Redman, S.J., and Segev, I. (1992). Matching dendritic neuron models to experimental data. Physiol Rev 72, S159–186.

Reuter, H. (1967). The dependence of slow inward current in Purkinje fibres on the extracellular calcium-concentration. J Physiol 192, 479–492.

Reuter, H. (1974). Exchange of calcium ions in the mammalian myocardium. Mechanisms and physiological significance. Circ Res 34, 599–605.

Reuter, H., Stevens, C.F., Tsien, R.W., and Yellen, G. (1982). Properties of single calcium channels in cardiac cell culture. Nature 297, 501–504.

Rink, T.J., Tsien, L.Y., and Tsien, R.W. (2016). Roger Yonchien Tsien (1952–2016). Nature 538, 172.

Rougier, O., Vassort, G., and Ildefonse, M. (1968). [Qualitative analysis by voltage-clamp of the membrane current of the skeletal muscle fiber]. C R Acad Hebd Seances Acad Sci D 266, 1754–1757.

Ryan, T.A., Reuter, H., Wendland, B., Schweizer, F.E., Tsien, R.W., and Smith, S.J. (1993). The kinetics of synaptic vesicle recycling measured at single presynaptic boutons. Neuron 11, 713–724.

Sather, W.A., and McCleskey, E.W. (2003). Permeation and selectivity in calcium channels. Annu Rev Physiol 65, 133–159.

Sather, W.A., Tanabe, T., Zhang, J.F., Mori, Y., Adams, M.E., and Tsien, R.W. (1993). Distinctive biophysical and pharmacological properties of class A (BI) calcium channel alpha 1 subunits. Neuron 11, 291–303.

Schneider, M.F., and Chandler, W.K. (1973). Voltage dependent charge movement of skeletal muscle: a possible step in excitation-contraction coupling. Nature 242, 244–246.

Shin, W., Ge, L., Arpino, G., Villarreal, S.A., Hamid, E., Liu, H., Zhao, W.D., Wen, P.J., Chiang, H.C., and Wu, L.G. (2018). Visualization of membrane pore in live cells reveals a dynamic-pore theory governing fusion and endocytosis. Cell 173, 934–945 e912.

Siegelbaum, S.A., and Tsien, R.W. (1980). Calcium-activated transient outward current in calf cardiac Purkinje fibres. J Physiol 299, 485–506.

Stricker, C., Field, A.C., and Redman, S.J. (1996). Changes in quantal parameters of EPSCs in rat CA1 neurones in vitro after the induction of long-term potentiation. J Physiol 490 (Pt 2), 443–454.

Takahashi, T., and Momiyama, A. (1993). Different types of calcium channels mediate central synaptic transmission. Nature 366, 156–158.

Tsien, R.W. (1973). Adrenaline-like effects of intracellular iontophoresis of cyclic AMP in cardiac Purkinje fibres. Nat New Biol 245, 120–122.

Tsien, R.W. (1974a). Effects of epinephrine on the pacemaker potassium current of cardiac Purkinje fibers. J Gen Physiol 64, 293–319.

Tsien, R.W. (1974b). Mode of action of chronotropic agents in cardiac Purkinje fibers. Does epinephrine act by directly modifying the external surface charge? J Gen Physiol 64, 320–342.

Tsien, R.W. (2007). A remembrance of Professor TP FENG. Sheng Li Xue Bao 59, 713–715.

Tsien, R.W., and Barrett, C.F. (2004). A brief history of calcium channel discovery (Austin, TX: Landes Bioscience).

Tsien, R.W., Fox, A.P., Hess, P., McCleskey, E.W., Nilius, B., Nowycky, M.C., and Rosenberg, R.L. (1987). Multiple types of calcium channel in excitable cells. Soc Gen Physiol Ser 41, 167–187.

Tsien, R.W., Giles, W., and Greengard, P. (1972). Cyclic AMP mediates the effects of adrenaline on cardiac purkinje fibres. Nat New Biol 240, 181–183.

Tsien, R.W., and Malinow, R. (1990). Long-term potentiation: presynaptic enhancement following postsynaptic activation of Ca(++)-dependent protein kinases. Cold Spring Harb Symp Quant Biol 55, 147–159.

Tsien, R.W., and Noble, D. (1969). A transition state theory approach to the kinetics of conductance changes in excitable membranes. J Membr Biol 1, 248–273.

Tsien, R.W., and Weingart, R. (1974). Proceedings: Cyclic AMP: cell-to-cell movement and inotropic effect in ventricular muscle, studied by a cut-end method. J Physiol 242, 95P–96P.

Tsien, R.W., and Weingart, R. (1976). Inotropic effect of cyclic AMP in calf ventricular muscle studied by a cut end method. J Physiol 260, 117–141.

Tsien, R.Y. (2010). Nobel lecture: constructing and exploiting the fluorescent protein paintbox. Integr Biol (Camb) 2, 77–93.

Tsien, R.Y., Green, D.P., Levinson, S.R., Rudy, B., and Sanders, J.K. (1975). A pharmacologically active derivative of tetrodotoxin. Proc R Soc Lond B Biol Sci 191, 555–559.

Vereecke, J., and Carmeliet, E. (1971). Sr action potentials in cardiac Purkyne fibres. II. Dependence of the Sr conductance on the external Sr concentration and Sr-Ca antagonism. Pflugers Arch 322, 73–82.

Wang, H.G., Lu, F.M., Jin, I., Udo, H., Kandel, E.R., de Vente, J., Walter, U., Lohmann, S.M., Hawkins, R.D., and Antonova, I. (2005). Presynaptic and postsynaptic roles of NO, cGK, and RhoA in long-lasting potentiation and aggregation of synaptic proteins. Neuron 45, 389–403.

Watson, J.D. (1968). The double helix: a personal account of the discovery of the structure of DNA (London: Weidenfeld and Nicolson).

Weidmann, S. (1966). The diffusion of radiopotassium across intercalated disks of mammalian cardiac muscle. J Physiol 187, 323–342.

Wheeler, D.B., Randall, A., and Tsien, R.W. (1994). Roles of N-type and Q-type Ca2+ channels in supporting hippocampal synaptic transmission. Science 264, 107–111.

Wheeler, D.B., Randall, A., and Tsien, R.W. (1996). Changes in action potential duration alter reliance of excitatory synaptic transmission on multiple types of Ca2+ channels in rat hippocampus. J Neurosci 16, 2226–2237.

Williamson, A.V., and Sather, W.A. (1999). Nonglutamate pore residues in ion selection and conduction in voltage-gated Ca2+ channels. Biophys J 77, 2575–2589.

Wu, J., Yan, Z., Li, Z., Qian, X., Lu, S., Dong, M., Zhou, Q., and Yan, N. (2016). Structure of the voltage-gated calcium channel Ca(v)1.1 at 3.6 A resolution. Nature 537, 191–196.

Wu, J., Yan, Z., Li, Z., Yan, C., Lu, S., Dong, M., and Yan, N. (2015). Structure of the voltage-gated calcium channel Cav1.1 complex. Science 350, aad2395.

Yang, J., Ellinor, P.T., Sather, W.A., Zhang, J.F., and Tsien, R.W. (1993). Molecular determinants of Ca2+ selectivity and ion permeation in L-type Ca2+ channels. Nature 366, 158–161.

Yue, D.T., and Marban, E. (1990). Permeation in the dihydropyridine-sensitive calcium channel. Multi-ion occupancy but no anomalous mole-fraction effect between Ba2+ and Ca2+. J Gen Physiol 95, 911–939.

Zhang, F., Wang, L.P., Boyden, E.S., and Deisseroth, K. (2006). Channelrhodopsin-2 and optical control of excitable cells. Nat Methods 3, 785–792.

Zhang, J., Campbell, R.E., Ting, A.Y., and Tsien, R.Y. (2002). Creating new fluorescent probes for cell biology. Nat Rev Mol Cell Biol 3, 906–918.

Zhang, Q., Cao, Y.Q., and Tsien, R.W. (2007). Quantum dots provide an optical signal specific to full collapse fusion of synaptic vesicles. Proc Natl Acad Sci USA 104, 17843–17848.

Zhang, Q., Li, Y., and Tsien, R.W. (2009). The dynamic control of kiss-and-run and vesicular reuse probed with single nanoparticles. Science 323, 1448–1453.

Zhao, Y., Huang, G., Wu, Q., Wu, K., Li, R., Lei, J., Pan, X., and Yan, N. (2019). Cryo-EM structures of apo and antagonist-bound human Cav3.1. Nature 576, 492–497.

Index

Abdelmoumene, S., 209

Abell, F., 95

Acsády, L., 63

Adachi, Y., 255

Adams, M., 512

Adler, E. M., 478, 486, 488, 499, 505

Adrian, R., 472, 473, 494, 495, 496, 498, 501

Aebischer, P., 212

Aggleton, J. P., 354

Ahmed, M., 521

Alabi, A. A., 513, 521

Alberini, C., 212, 329

Albery, J., 493

Albinus, B. S., 458

Albright, T., 40, 180, 242

Alda, A., 343

Aldrich, R., 507, 510

Allaman, I., 207, 209, 210, 212, 213

Allen, J., 481

Allen, P., 415

Almers, W., 503, 505

Alvarez, P., 334, 339

Alvarez-Bolado, G., 441, 447

Alvarez-Buylla, A., 409

Alvarez-Royo, P., 339, 363

Amara, S., 440, 441

Amaral, D., 333, 336, 339, 340, 437

Andén, N., 7

Andersen, P., 282

Anderson, J. R., 242

Andrews, T., 297, 299

Ansermet, F., 217

Antal, M., 61

Antonini, A., 394, 401, 403, 419

Antonov, I., 513

Arancio, O., 513

Aravanis, A., 520

Arbib, M., 451, 452

Arminjon, M., 217

Armstrong, C. M., 503, 504, 506, 508

Armstrong, J., 271

Aronov, D., 358

Arriza, J., 441

Arroyo, M., 26

Asadollahi, A., 165, 166

Aston-Jones, G., 194, 200, 201

Aswad, D., 106, 121

Augustine, G., 307, 308, 309

Aurnhammer, W., 76, 77, 91

Axelrod, J., 190

Ayres, B., 110

Azmitia, E., 459

Baccus, S., 482

Bader, P., 521

Badre, D., 242, 245

Baetscher, M., 106

Bak, L. K., 210

Baker, G., 418

Baker, P. F., 473, 494, 495, 497

Balaban, C. D., 233

Balázs, J., 70, 70n2

Balleine, B., 20, 22, 28

Baltes, P., 80

Bannister, J., 496

Barinaga, M., 446

Barlow, H., 385, 494

Barlow, N., 361

Barnes, C., 23, 106

Baron-Cohen, S., 91, 92

Barondes, S., 328

Barrett, C. F., 495, 520

Barron, R., 85

Barros, F., 204, 210

Barroso, J. M., 67

Barth, J., 182

Barthes, R., 187, 214

Bartol, T., 106

Bashir, Z. I., 512

Batini, C., 233

Baum, M., 5, 15

Bayley, P. J., 335, 336, 337, 346, 349, 363

Baylor, D., 150, 171, 407

Beach, F., 5

Bean, B., 505, 506, 517

Beardsley, A., 230

Beaudet, A., 194

Beckett, S., 491

Beech, R., 81

Behrens, M., 106

Bekavec, N., 498

Belafonte, H., 428

Bélanger, M., 213

Belin, D., 24, 28, 29, 32, 40

Belin-Rauscent, A., 29

Belmonte, C., 214

Benham, C., 517

Bennett, M., 124, 128, 133, 476

Benson, D. F., 245

Bentivoglio, D. M., 437

Benzer, S., 391

Benzing, W., 345

Berg, P., 509

Bergan, J., 159, 160, 161, 163

Bergeron, J., 488

Bergman, S. J., 491, 492, 493, 498

Bergsman, J., 517

Berl, S., 208

Berliner, R., 508

Bernardinelli, Y., 210

Berridge, K., 24

Berrigan, D., 113

Berrigan, P., 113

Berthet, C., 213

Besia, G., 183

Best, P., 381

Betz, W. J., 513

Bezprozvanny, I., 518

Bhatla, N., 418

Bindra, D., 12

Bishop, D. V. B., 83

Bishop, J. M., 400, 402

Bito, H., 513, 518

Bittar, P. G., 209

Bizzi, E., 327, 388

Björklund, A., 58, 60

Bjorkman, P., 106

Blakemore, C., 310, 385, 387, 494, 505

Blakemore, S., 87

Blasdel, G., 149

Blaustein, M., 284, 494

Bley, K., 517

Bliss, T. M., 213, 238, 282

Bloch, K., 190

Bloom, F. E., 193, 194, 195, 196, 197, 198, 199, 200, 202, 204, 205, 208, 214, 438

Bloom, J., 205

Boesch, E., 80

Bolam, P., 58

Bolis, C., 180

Bolis, F., 180, 181

Bolis, G., 180

Bolis, L., 190

Bolis, P., 181

Bonhoeffer, T., 398, 404

Bontempi, B., 335

Booth, C., 511

Boron, W., 508

Bose, A. G., 482

Bota, M., 452, 453, 454, 455

Boulpaep, E., 508

Boury-Jamot, B., 212

Bouzat, P., 213

Bowden, D., 452

Bowling, D., 306, 309, 310, 311, 312, 316, 317

Bowra, M., 487, 488, 505

Boyd, I. A., 498

Boyden, E., 497, 511, 520

Bradley, B., 485

Bradley, E., 413

Bradshaw, R., 435

Bragg, L., 473

Brainard, M., 157

Braitenberg, V., 208, 213

Breiter, H., 453

Brenner, S., 308

Brittain, D., 443, 454

Broadbent, D., 237

Broadbent, N., 342, 343, 363

Brockes, J., 124

Brodman, E., 457

Bröer, S., 209

Bronner, M., 106

Brooks, G. A., 209

Brown, A. M., 460, 502

Brown, G. L., 493

Brown, J., 430, 485

Brown, M. W., 289, 354

Brown, R., 89, 453, 454

Brubeck, D., 483

Bruner, J., 89

Brunet, J.-M., 209

Brunger, A., 510

Bryant, A., 167

Bryant, P., 89

Bucher, M. B., 191

Buckley, M., 238

Buckner, R. L., 242, 245

Buffalo, E. A., 340, 348, 358, 363

Bugnon, C., 449

Bullmore, E., 33

Bullock, T., 144, 145, 146, 147, 150

Bunge, R., 457

Bunge, M., 457

Bunsell, D., 4

Burgess, P., 96

Burns, G., 451, 452

Burt, D. R., 191

Burton, G., 483

Burton, K., 460

Bussey, T., 22

Buttigieg, P., 107

Buzsáki, G., 60, 61, 62, 65, 67, 474, 515

Byerly, L., 503

Cadas, H., 209

Cador, M., 14, 15, 16

Cahill, J., 476

Cajal, S. R., 426, 457, 458, 459

Calabresi, G., 498

Cali, C., 215

Calvin, J., 203

Campbell, F., 494

Campbell, J., 106

Cang, J., 406, 407, 408, 418

Canteras, N., 445, 446, 448, 449

Cantor, B., 476

Cao, Y., 520

Carbone, E., 506

Cardinal, R., 20, 21, 22, 24

Cardinaux, J. R., 210

Carmeliet, E., 503

Carrard, A., 204, 213

Carson, J., 440

Carteron, L., 213

Case, J., 142, 143, 144, 145, 150, 171

Casey, P., 307, 309, 310

Castelli, F., 93, 95

Catalano, S., 106

Cataldi, M., 504, 520

Catsicas, S., 215

Catterall, B., 113

Cavanaugh, P., 244

Cave, C., 350, 363

Cawkell, G., 493

Caywood, M., 418

Cenquizca, L. A., 449, 450

Chamberland, S., 522

Chandler, W. K., 472, 473, 497, 498, 501, 507, 508

Chang, H. S., 240, 241

Chang, I., 478

Chan-Palay, V., 233

Chapman, B., 397, 398, 399, 417

Chatton, J.-Y., 209, 210

Chavkin, C., 195

Chen, G., 519

Chen, X. H., 504, 519

Chenouard, N., 513, 521

Chevreul, M., 298

Chiamvimonvat, N., 491

Chikazoe, J., 25

Choi, H. B., 204

Choi, J., 306

Choi, S., 519

Cholet, N., 210

Chomsky, N., 97, 253

Christakou, A., 20

Chu, S., 485, 511

Chun, M., 455

Cicero, 186

Cicero, T., 431

Clapham, D., 507

Clarke, R., 334, 341, 342, 343, 352, 353, 363

Clarke, V., 3

Clarke, W., 488, 498

Clavier, R., 441

Clement-Cormier, Y. C., 191

Cline, H., 517

Clinton, B., 493, 498

Clinton, H., 499

Coen, C., 450

Cohen, C. J., 516

Cohen, L., 495, 497, 498, 508

Cohen, N., 323, 330, 344, 347, 363

Cohen, S. M., 434, 472, 513, 522

Cohen, Y., 158

Colatsky, T. J., 501, 516

Coltrane, J., 54

Conroy, M. A., 351

Constantine-Patton, M., 106

Cools, A., 23

Cooper, R., 427

Cooper, W. C., 458

Copenhagen, D., 407

Corbit, L., 20, 22

Cori, C., 190

Corridoni, S., 183

Costantin, L., 473

Cowan, J. D., 244

Cowan, M., 291, 296, 432, 433, 434, 435, 436, 437, 445, 446, 447, 456, 457, 458, 509

Cowey, A., 237

Coyle, J., 199

Crabtree, G., 509

Craig, N., 325

Crair, M., 401, 418

Crayton, C., 460

Crespo, S., 476

Crick, F., 57, 163, 197, 200, 391, 429, 438, 451, 452, 453

Cromer, R., 89, 90, 97

Cronkite, W., 113

Dadarlat, M., 411, 418

Dadvand, L., 418

Dahlstöm, A., 434

Dale, H. H., 119

Dalley, J., 17, 27, 32

Damasio, A., 217

Dang, T. X., 503, 504

D’Angour, A., 186

Danker, J. F., 242

Darcy, D., 418

Darwin, C., 360, 498

Das, R. K., 38

Dashti, A. E., 451, 452

Davidson, N., 128, 129, 511

Davis, H., 329

Davis, M., 54, 509

Daw, N., 284

Dawkins, P., 485, 489

Dawson, G., 17

Dayer, A., 216

DeBello, W., 159

De Bernardi, R., 209

DeCamilli, P., 106, 121

Dede, A. J., 336, 355, 357, 363

Degtyar, V., 519

Dehaene, S., 257

Deisseroth, K., 257, 497, 510, 513, 517

Delcour, A., 517

Démonet, J., 86

Dennett, D. C., 244

Dennis, M., 392

Derges, S., 81

Deroche-Gamonet, V., 32

Desa, V., 418

Descarries, L., 194

Descartes, R., 254, 505

Desimone, R., 242, 253

Deutsch, J. A., 326

Devarajan, S., 168

Devinsky, O., 515

Dewey, M., 94

Di Ciano, P., 33

Diamond, J., 494

Dickinson, T., 20, 22, 24, 25, 28, 30

Divine, L., 460

Djamgoz, M. B., 191

Dolan, R., 96

Dolivo, M., 205

Dolphin, A., 121

Dong, H., 449, 452, 453

Dorne, B., 110

Douglas, R. J., 250

Doyle, J., 453

Dräger, U., 118, 402

Draper, C., 482

Draper, J., 482

Driver, J., 96, 237

Druckenmiller, S., 514

Dryander, J., 458

du Lac, S., 154, 155

Dubach, M. F., 452

Dubel, S. J., 512

Dufosse, M., 233, 235

Dugan, R., 106

Duncan, J., 238

Dunlap, K., 512

Dunn, L., 18

Dyballa, L., 412

Eacott, M., 238, 239

Early, S., 488

Ebashi, S., 232

Eccles, J., 57, 282, 492, 496

Economidou, D., 32

Ehlers, M., 314

Ehri, L., 85

Eichenbaum, M. S., 356

Einaudi, E., 511

Eisenman, G., 508

Ellinor, P., 503, 512, 517

Ellsberg, D., 113

Elsayed, M., 217

Embick, D., 253

Emmanuel, V., 184

England, P., 406

Enna, S. J., 191

Epstein, S. B., 479, 480

Erdo˝, P., 66

Erickson, C. A., 242

Erondu, N., 124, 133

Ersche, K., 32

‘Espinasse, P., 3

Espinosa, J. S., 418

Esterly, S., 152, 154, 156

Evans, R., 440, 441, 442, 447

Everitt, A., 40

Everitt, B. J., 1, 2, 5, 8, 12, 14, 15, 16, 17, 18, 20, 21, 22, 25, 26, 27, 29, 33, 34, 35

Everitt, F., 2

Everitt, Jane, 25, 40

Everitt, Jessica, 25, 40

Everitt, M., 2

Everitt, W., 2

Eyring, K. W., 513, 522

Fagiolini, M., 403, 404, 418

Falck, B., 7, 200

Fambrough, D., 113, 114

Fatt, P., 280

Feher, G., 360, 362

Feldheim, D., 406, 407, 408

Feldman, D., 157, 158, 170, 506

Feliciano, J., 483

Fellmann, D., 449

Feng, T. P., 507

Ferron, A., 426

Ferron, W. E., 426

Feynman, R., 362

Fields, H., 392

Fink, G., 444

Finsterwald, C., 217

Fischbach, G., 291

Fishell, G., 515

Fitzpatrick, D., 314

Fiumelli, H., 209, 215

Flagel, S., 22

Flamm, E., 458

Flanagan, O., 244

Fleckenstein, A., 502

Fletcher, P., 92

Folkman, J., 274, 275, 276

Fontana, L., 360

Foote, S., 194, 195, 196, 201

Fortunato, S., 456

Foscolo, U., 182

Foucalt, M., 214

Fox, A., 505, 506, 517

Fox, P. T., 210

Frackowiak, R., 96, 252, 253

Frambach, M., 345

Frankel, S., 510, 511

Frankland, P. W., 335

Franklin, R., 57, 473

Frascino, J., 360

Freeman, J. A., 249

Fresco, P., 515

Freud, S., 216, 217

Freund, A., 62

Freund, E., 62

Freund, T. F., 51, 52, 58, 59, 60, 61, 63, 65, 66, 70

Friederici, A., 253

Friel, D., 517

Friston, K., 96, 252

Frith, A., 82, 98

Frith, C., 75, 81, 82, 83, 84, 86, 96, 98, 99

Frith, M., 82

Frith, U., 75, 76, 82, 83, 84, 85, 86, 87, 89, 90, 91, 92, 94, 95, 97, 98, 99

Froemke, R., 515

Fu, Y., 410, 411, 418

Furshpan, E., 117, 118, 272

Furster, D., 119

Fuxe, K., 7, 8, 9, 13, 14, 434

Fye, B., 458

Fyhn, M., 418

Fyhn, T. H., 418

Gaffan, D., 237, 238, 243

Gage, F., 60, 61

Gajdusek, C., 190

Gallagher, A., 85

Gallagher, M., 20

Galli, L., 399, 407

Gallistel, C. R., 383

Gamow, G., 230, 231, 259

Gandhi, S., 409, 418

Gao, V., 210

Garau, L., 192

Garcia, C., 510

Garibaldi, G., 184

Gazzaniga, M., 245, 246

Gelperin, A., 143

Gerber, G. J., 26

Gerfen, C., 441, 442

Getting, P., 483

Getz, S., 483

Geyer, A., 25

Geyer, M., 25

Ghelarducci, B., 233

Giebisch, G., 497, 500, 501, 508

Gilbert, C., 119

Giles, W., 499, 516

Gill, K., 306, 310, 311, 317

Gillberg, C., 94

Gillespie, D. C., 406, 418

Gilly, W., 507

Gilman, H., 446

Giordano, M., 459

Giuliana, C., 180

Giuliano, C., 31, 32, 33, 34

Giulietti, I., 182

Giulio, P., 181, 182, 183

Gleitman, L., 85

Glenn, A., 426

Glenn, J., 426

Glickfeld, L., 520

Glowinski, J., 6, 208

Goddard, A., 167

Goddard, G., 326

Goelz, S., 106, 121, 133

Goentoro, L., 106

Gold, D., 436, 437

Gold, J. J., 158, 160, 336, 363

Goldberg, M., 238, 384, 385

Goldberg, S. R., 13

Golgi, C., 459

Gong, J., 444, 445, 449

Goodman, B., 53, 54

Goodman, M., 510

Goodrich, J. T., 460

Gordon, J., 402, 403, 418

Gordon, L., 114, 115

Gorski, R., 442

Goto, M., 450

Gottlieb, D., 457

Gradwell, P., 6

Graf, P., 350

Granit, R., 234

Grassi, F., 181

Grastyán, E., 67

Gray, P., 482

Graybiel, A., 233

Greengard, P., 119, 120, 121, 122, 123, 124, 125, 127, 129, 191, 193, 205, 446, 500

Grivald, A., 404

Groenewegen, H., 22

Gross, C., 239, 249, 327, 402

Grossman, R., 514

Grossman, S. P., 431, 432, 436, 450

Groth, R., 511, 513, 521

Grzanna, R., 199

Guillemin, R., 195, 438

Guillery, R. W., 397

Gulyás, A. I., 61, 63, 66

Guo, P. F., 314

Gutfreund, Y., 159, 160

Gutierrez, G., 294

Haber, S., 28

Hagelin, O., 458

Haggard, P., 96

Hagiwara, S., 503, 505, 506

Haglund, L., 443

Hahn, J., 450, 454, 455, 456

Haist, F., 363

Hájos, N., 63, 65

Hall, J., 20, 22, 34, 35

Hall, Z., 114, 117, 132, 133, 391, 392, 399

Haller, J., 65

Halmos, P., 380

Hamann, S. B., 349, 363

Hamburger, V., 287, 288

Hamill, O. P., 501

Hámori, J., 53

Hampton, F., 116

Hampton, R. R., 254

Han, J. S., 20

Han, X., 520

Hanani, M., 522

Handel, G. F., 479

Hanover, J. L., 418

Hansen, S., 11

Happé, F., 89, 92, 93, 94, 95

Harata, N. C., 521

Hardy, T., 481

Hargrove, S., 360

Harkmark, W., 457

Harris, B., 391, 392, 393

Harris, K. D., 106, 250

Harris, S. S., 419

Hart, H. L. A., 493, 498

Hart, J. T., 254

Hartley, M., 460

Hartman, B., 435, 436

Hasegawa, I., 247

Haseltine, W. A., 515

Hasselmo, M., 237

Hastings, M., 10

Hata, Y., 401, 418

Hausser, M., 494

Hauswirth, O., 491, 500, 501

Hayashi, T., 248

Hayden, T., 116

Haymaker, W., 435

He, X., 441

Heath, E., 9

Hebb, D., 234, 326

Hegel, G. W. F., 479

Heider, F., 93

Heiligenberg, W., 146, 171

Hein, A., 386

Held, R., 327

Hellemans, K., 38

Heller, J., 491

Helmholtz, H., 298, 417

Henderson, L., 325

Henning, D., 429

Hensch, T. K., 233, 257, 401, 403, 404, 418

Herbert, J., 4, 5, 9, 10, 40

Hermelin, B., 87, 88, 89

Hess, P., 502, 503, 504, 506, 507, 517

Hessler, C., 488, 498

Heuser, J., 392

Heyworth, N. C., 357, 363

Highstein, S. M., 233

Higuchi, S., 243, 246

Hildebrand, J., 118

Hill, A. V., 280, 507

Hillarp, N., 7

Hille, B., 476, 508

Hinde, R., 5

Hirabayashi, T., 248, 249, 250

Hirning, L. D., 506

Hirsch, H., 388

Hitler, A., 487

Ho Chi Minh, 113

Hodgkin, A. L., 113, 118, 283, 317, 472, 473, 474, 489, 493, 494, 495, 496, 498, 501, 503, 507, 513

Hof, P. R., 204, 452

Hoffer, B., 194

Hoffman, J., 190, 508

Hogan, M., 312

Hökfelt, T., 7, 9, 12, 197, 445

Holland, P., 20

Hollyday, M., 449

Hood, L., 128, 129, 133, 134, 135

Hoover, J. E., 117

Hopkins, G. M., 379

Horne, W., 512, 517

Horowicz, P., 472, 473

Horridge, A., 144

Horton, J., 418

Hoseini, M. S., 409, 412, 418

House, J., 457

Huang, J., 403, 410

Huang, L. M., 507

Hubel, D. H., 118, 239, 272, 277, 278, 284, 295, 385, 388, 389, 390, 391, 392, 397, 402, 410, 443, 493

Huberman, A. D., 399

Hudspeth, J., 122, 123

Huerta, M. F., 451

Hufstedler, S., 132, 133

Huggins, C., 484

Hughes, A., 15

Hunt, C., 283, 284, 285, 287, 291, 432, 498

Hurvich, L., 295

Husserl, E., 254, 259

Hutcheson, D. M., 30

Hutter, O., 489, 507

Huttner, W., 121

Huxley, A., 113, 118, 280, 283, 317, 474, 489, 493, 494, 495, 496, 498

Hyde, P., 159, 160

Iggo, A., 494

Insausti, R., 336

Insel, T., 453

Irace, F., 181

Isaacson, J., 493, 517

Ishai, A., 243

Issa, N., 418

Ito, M., 232, 233, 234, 235, 236, 237, 243, 258, 259, 403

Ito, R., 20, 23, 26, 27

Itoh, Y., 210

Iversen, L., 6

Iversen, S., 13, 15, 338

Jack, J. J., 472, 488, 490, 492, 493, 494, 496

James, W., 254

Jameson, D., 295

Jammes, I., 209

Janak, P., 19

Janowsky, J., 354, 363

Jansen, J., 289

Jarvik, M., 327, 328

Jastreboff, P. J., 233

Jeanrenaud, B., 190, 191

Jefferson, T., 115

Jeneson, A., 363

Jéquier, E., 207, 213

Jeub, L., 456

Johnson, C., 459

Johnson, K., 443

Johnson, L. B., 114, 380, 488

Johnson, M., 10, 12

Johnson, R., 459

Johnson, T., 501

Johnston, D., 106

Jones, A., 415

Jones, H., 480, 482, 485, 493, 496

Jones, P. J., 70

Jones, T., 457, 458

Jongen-Relo, A., 22

Jonkman, S., 31

Jonsson, G., 7

Joseph, R., 485

Jourdain, P., 213, 216

Joyce, M., 427

Judd, L., 359

Jun, K., 512

Kaas, J., 396

Kaczmarek, L., 482

Kadekaro, M., 207

Kado, R. T., 233

Kail, R., 85

Kalatsky, V., 404, 405, 418

Kamb, B., 132, 133

Kamigaki, T., 252

Kandel, E., 127, 129, 248, 360

Kaneko, M., 405, 406, 411, 418

Kanwisher, N., 243

Karachot, L., 233

Karnovsky, M., 190

Karten, H., 197, 327, 458

Kass, R. S., 491, 499, 501, 507, 516

Katona, I., 63, 65, 66

Katz, B., 118, 272, 277, 278, 279, 280, 281, 282, 283, 284, 285, 317, 474, 494, 495, 496, 498, 515

Katz, L., 314

Kauer, J., 517

Kavalali, E., 519

Kebabian, J., 191

Keller, J. B., 395

Kelley, A., 15

Kelley, D. E., 460

Kelley, P. T., 124

Kelly, J., 436

Kendall, D., 487, 498

Kennedy, B., 106

Kennedy, J. F., 114, 377, 382, 430

Kennedy, Janet, 106

Kennedy, Jean, 106

Kennedy, M. B., 105

Kennedy, N., 106

Kennedy, R., 430

Kennedy, T., 106

Kenyatta, J., 382

Kerr, S. E., 198

Keverne, B., 5, 10

Keynes, J. M., 217

Keynes, R. D., 190, 205, 494, 496, 498, 503, 508

Kiang, N., 485, 486

Kikyo, H., 236, 254, 256

Killcross, S., 18

Kim, J., 520

Kim, S., 343, 356, 357, 363

Kimerer, L. M., 201

Kindt, M., 38

King, M. L., 326, 378, 430

Kiraly, M., 209

Kirk-Fulton, L., 510

Kirkwood, P., 391

Kirwan, C. B., 336, 354, 355, 363

Kitchener, E., 363

Klein, J., 458

Klingauf, J., 519

Knowlton, B. J., 345, 363

Knudsen, C., 156

Knudsen, E. I., 139, 140, 143, 145, 147, 148, 149, 150, 151, 152, 153, 154, 155, 157, 158, 159, 160, 162, 163, 164, 166, 168, 169, 170, 171

Knudsen, K., 156

Knudsen, P., 145, 146, 147, 150, 151, 152, 153, 154, 156, 164, 167, 168, 169, 170, 172

Knutson, A. R., 343, 363

Kobilka, B., 510, 511

Koch, D., 482

Koch, J., 482

Koch, W., 482

Kodály, Z., 70

Köhler, C., 443

Kongsamut, S., 517

Konishi, M., 128, 129, 139, 146, 147, 148, 149, 150, 151, 152, 171

Konishi, S., 252

Konorski, J., 12, 326

Koob, G., 25

Korn, D., 510

Koslow, S., 452

Kostyuk, P. G., 503

Kötter, R., 453

Kottler, M., 458

Koyama, M., 255

Koyano, K. W., 248, 250

Krasne, S., 505

Kravitz, E., 117, 279, 284

Krebs, E., 126

Kreutzfeldt, O., 281

Krishnan, R., 307, 310, 313

Kritchevsky, M., 332, 359

Kuffler, S., 117, 126, 272, 273, 276, 278, 279, 280, 281, 282, 283, 284, 317, 417, 485, 486, 489, 491, 498, 510, 515

Kullmann, D., 494

Kuo, C. C., 503, 504

Kuypers, H. G., 435, 436, 437, 458

LaBelle, J., 130, 132, 133

Lam, H., 520

LaMantia, A., 292, 293

Landau, B., 432

Landerl, K., 91

Landis, S., 117

Lange, P., 315

Langley, J., 285, 286

Langone, K., 514

Lansman, J., 517

Larkin, E., 482

Larkman, A., 512

Lasensky, E., 511

Laughton, J., 209

Law, M. I., 418

Lawson, R. P., 89

Lay, Cary, 205

Lease, B., 124

Leblanc, O., 484

Lederer, W. J., 499, 516

LeDoux, J., 18

Lee, J., 20, 35, 36, 37, 38

Lee, K. S., 502, 516

Lee, M., 410

Lee, S., 481

Lefkowitz, R., 511

Leibowitz, S., 437

Lengacher, S., 217

Lennarz, W., 115

Leonesio, R. J., 254

Lepore, J., 473

Leslie, A. M., 90, 91, 92

Leslie, S., 90, 91

Lester, H., 106, 485, 511

Lettvin, J., 389

LeVay, S., 118, 390, 392, 397, 443

Levelt, W., 253

Leventhal, A., 388

Levi-Montalcini, R., 202, 288, 434, 435

Levine, S., 326

Lévi-Strauss, C., 187, 214

Levy, D. A., 351, 363

Levy, R., 418

Lewis, D., 458

Lewis, R., 510

Li, B., 513, 521

Li, L., 521

Li, Y. T., 475, 481, 521

Liao, Y. J., 521

Liberman, I., 85

Lichtman, J., 287, 289, 290, 291, 294, 455

Lieberman, M., 501

Lin, D., 515

Lind, W., 443

Lindskog, M., 520

Linkenhoker, B., 159, 160

Lipscombe, D., 507, 517

Lisberger, S., 314, 315, 400

Lisman, J., 125, 126

Liss, P., 326, 327

Liu, G., 513, 517

Liu, J., 522

Livingstone, M., 106, 119

Llinás, R., 496, 506, 514

Locke, D., 98

Loewy, A., 435, 457

Logothesis, N., 255, 257

Lømo, T., 282

Long, F., 301, 302

Loomis, B., 106

Lotto, B., 299, 300, 301

Löwel, S., 419

Lowry, O., 198, 432

Luebke, J. I., 512

Lupinski, J., 484

Luria, S., 485

Luthi, A., 19

Lux, H. D., 506

Lynen, F., 190

Lyons, A., 458

Ma, H., 513, 521

Macdonald, R., 483, 485, 505

Mackie, K., 65

MacKinnon, R., 113

Mackintosh, N., 19

MacNicol, P., 460

Maczko, K., 163, 164

Madison, D., 507, 510, 517

Maduke, M., 510

Maffei, L., 399, 407

Magistretti, A., 192, 203, 205, 211, 217

Magistretti, B., 203, 205, 211

Magistretti, C., 194, 197, 198, 199, 202, 203, 205, 211, 212, 214

Magistretti, F., 183

Magistretti, H., 203, 212

Magistretti, L., 182

Magistretti, M., 180, 182, 183

Magistretti, Philippe, 185, 188

Magistretti, Pier G., 180, 182, 183, 185

Magistretti, Pierre J., 179, 180, 185, 193, 199, 200, 201, 202, 204, 207, 208, 209, 210, 211, 213, 216, 217

Magistretti, V., 181, 182, 183

Magrassi, L., 290

Mahoney, D., 214

Mahut, H., 337

Maillard, M., 209

Main, J. F., 479, 484

Maisky, V. A., 435

Makara, J. K., 66

Malenka, R. C., 405

Malgaroli, A., 512, 513, 517

Malick, T., 487

Malinow, R., 507, 512, 517

Malpeli, J., 485

Mandel, B., 477

Mandelberg, N., 522

Mannheim, K., 231

Manns, J., 334, 352, 363

Mantle, M., 475

Mao Tse Tung, 114

Marantz, A., 253

Marban, E., 503, 504, 516

Marcos, F., 418

Marder, E., 106

Margineanu, M., 213

Maril, A., 254

Markakis, E., 448, 449

Markou, A., 25, 26

Markram, H., 212

Marquet, P., 209, 216

Marr, D., 239, 259

Marsh, G., 85

Martin, A. R., 498

Martin, J. C., 451

Martin, J. L., 204, 206, 209, 213, 215, 217

Martin, K., 60

Martin, K. A. C., 250

Martínez-Guijarro, F. J., 61

Martone, M., 454

Masao. See Ito

Masino, T., 154, 155, 158

Mathys, C., 89

Matsui, T., 248, 249

Matsuzaki, M., 251

Matteson, D. R., 506

Mauldin, K., 363

Mays, W., 475

Mazzone, J., 480

Mboya, T., 382

McAfee, D. A., 191

McAllister, A. K., 513

McAlonan, G., 17

McCarthy, G., 380, 430

McCarthy, J., 478

McCleskey, E. W., 503, 504, 505, 506, 512, 517

McCollough, C., 325

McConnell, S., 397

McCormick, C., 358

McCoy, A., 299

McCrory, E., 95

McGaugh, J., 244, 360

McGaughy, J., 17, 18

McGovern, G., 189

McGuinness, T. L., 124

McHugh, P., 359

McIlwain, H., 210

McIntyre, A., 492

McKay, R., 106

McKee, R., 363

McLaughlin, T., 407

McMahan, J., 150, 279, 281, 284, 289, 515

McMilan, H., 382

McNamara, J., 314

McNaughton, B., 23

McTernan, J., 130, 133

McVicar, B., 204

Mehler, J., 89, 253

Meister, M., 407

Menon-Johansson, A., 517

Mercator, G., 447

Merleau-Ponty, M., 231, 254, 259

Merlo, E., 36

Mermelstein, P., 513, 519

Merzenich, M., 392, 395, 396

Meskenaite, V., 61

Messinger, A., 242

Metcalfe, J., 254

Meves, H., 507

Meyerson, B., 6

Meyner, R., 480

Middlebrooks, J., 154, 257

Miledi, R., 118, 280, 282, 496

Miles, F., 28

Miles, R., 61, 62, 63

Miljanich, G., 512

Miller, G., 159, 160

Miller, K. D., 393, 395, 417

Miller, R., 506

Miller, S., 124, 125, 126, 127, 133

Milner, B., 238, 251, 336, 344

Milner, P., 326

Milton, A., 20, 36, 38

Misanin, J. R., 35

Mishkin, M., 238, 243, 337, 338, 344, 360

Mitchell, D. E., 385, 387

Mitchell, P., 119

Mitra, A., 521

Mitra, P., 453, 454

Miyamoto, K., 235, 236, 255, 256, 257

Miyashita, N., 237, 402

Miyashita, Y., 229, 230, 235, 236, 238, 240, 241, 242, 243, 246, 248, 249, 250, 259

Módy, I., 62

Mogdans, J., 157

Mogenson, G., 15, 442, 450

Molliver, M., 199

Momiyama, A., 512

Monson, B., 312

Montagnier, L., 443

Monyer, H., 63

Mooney, R., 511

Moore, F., 273, 274, 275, 276

Moore, R., 431, 458

Moreno, R., 460

Morgenstern, Y., 312, 316

Morris, R., 335

Morrison, Abbie, 199, 205

Morrison, Alex, 199

Morrison, J. H., 195, 199, 200, 201, 204, 205, 207, 213, 459

Morrison, K., 199

Morton, J., 90, 96, 97, 98

Moser, E., 257

Movshon, T., 515

Moya, R., 522

Moyner, H., 106

Muller, A., 206

Mullins, C., 522

Mumford, D., 302

Murata, J., 244

Murray, B., 20, 238, 243

Murray, J., 29

Murthy, V. N., 513

Musen, G., 345, 363

Myelnikov, D., 440

Myers, R. D., 431

Mysore, S., 165, 166

Nader, K., 35

Nakahara, K., 255

Namkoong, Y., 519

Nathans, D., 509

Nauta, W., 15, 327, 435, 436, 437

Naya, Y., 242, 248, 250

Nebet, E., 522

Needleman, P., 432

Neher, E., 283, 501, 502

Nelson, J., 510

Nelson, R., 130, 133

Nelson, S. R., 198

Nelson, T. O., 254

Nerbonne, J. M., 491

Nestler, E., 106, 121

Neville, H., 253

Newcomb, R., 512

Newell, L. J., 378

Newsome, B., 156, 244, 257, 514

Neyton, J., 503, 504

Ng, C., 312, 316

Ngai, J., 514

Nicholls, J., 150, 277, 278, 279, 281, 295, 508

Nicholson, C., 249

Nicoll, R., 392, 492, 512

Niedergerke, R., 280

Niell, C., 409, 410, 418

Nikias, M., 446

Nilius, B., 502, 506, 507, 517

Nitta, Y., 232

Nixon, R., 189, 377, 380

Njå, A., 286

Noble, D., 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 496, 498, 500, 501

Noble, P., 490

Noble, S., 490, 499

Noe, K., 232

Norcia, T., 404, 405

Norman, D. A., 245

Norman, J., 458

Nowell, N., 3

Nowycky, M., 505, 506, 517

Numa, S., 503, 511, 512

Nundy, S., 303

Nunn, L. L., 378, 379

Nyiri, G., 63, 64

Nyitrai, E., 54

Ocampo, A., 363

O’Connor, N., 87, 88, 89, 90

O’Craven, K. M., 243

Ogawa, S., 251

Ohbayashi, M., 248

O’Keefe, J., 96, 238, 251

Okuno, H., 250

Olds, J., 381, 383

Olds, M. E., 381

O’Leary, D., 437

Olivera, B., 506, 512

Olmstead, C., 23, 30, 31

Olsen, J., 154, 155, 156

Olson, L., 7

Omori, S., 231

Oncken, E., 426

O’Neil, W., 253

Orban, G., 255

Orlov, I., 233

Osada, T., 255

Osten, P., 454

Owen, S., 521

Owens, M., 408, 418

Page, K., 17

Page, S., 280

Palacios, J. M., 204

Palade, G., 122, 508

Palay, S. L., 198

Paller, K., 363

Palmiter, R. D., 440

Pantani, V., 507

Park, H., 513, 521

Parkinson, J., 20, 22, 23

Parsons, T., 231

Pasca, V., 181

Passingham, D., 237

Passoneau, J., 198

Patterson, P., 114, 115, 117, 118

Paulesu, E., 86

Pázmány, P., 66

Peachey, L., 473

Peake, W., 486

Pearlman, A., 284

Pearson, K., 488, 489, 491, 496

Pechura, C. M., 451

Pellegrini, M., 459

Pellerin, L., 208, 209, 210, 211

Pelloux, Y., 31, 34

Pennartz, C., 23

Perez, V., 431

Perlman, A., 402

Perner, J., 91

Peters, A., 201

Petersen, S., 351

Petit, J. M., 209, 213

Petrides, M., 244, 251

Petrovich, G., 448, 449

Pettigrew, J., 147, 153, 385

Pham, T., 418

Phelps, C. H., 198

Piaf, É., 231

Piedras-Renteria, E., 520

Pierre, K., 209

Pilla, M., 33

Piomelli, D., 66, 208

Pitt, G., 520

Pittman, Q. J., 195

Platt, M., 314, 315

Pliteri, S., 181

Poburko, D., 521

Poeppel, D., 253

Poetter, B., 415

Poggio, T., 239

Pollen, D., 491

Polster, A., 472

Poo, M., 215, 514

Popper, K. R., 232

Potter, D., 117, 272, 276, 277, 279

Premack, D., 91

Press, G., 333

Pribram, K., 326

Price, J., 296, 456, 457

Pringle, J. W. S., 486

Priya, R., 409

Profitt, D., 511

Purves, D., 269, 270, 362

Purves, S., 277, 278, 279, 284, 285, 293, 294, 308, 309, 313

Pyle, J., 520

Qing Howe, C., 302, 303

Quach, T. T., 195, 196

Quack, T., 196

Quarton, G., 383

Quik, M., 197

Quine, W. V. O., 381

Raichle, M. E., 179, 210, 244, 351, 453

Rakela, B., 418

Rakic, P., 292, 293

Rall, T. W., 196

Rall, W., 494

Ramamurthy, D., 169

Ramus, F., 85

Ramus, S., 363

Randall, A., 512, 517

Rang, H., 496

Ravenel, S., 277, 278, 279, 284, 285, 293, 294, 308, 309, 313

Reber, P., 346, 363

Redford, R., 377

Redman, S. J., 490, 494

Reeb, J., 378

Reed, J. M., 333, 335, 337, 363

Rees, G., 89

Reese, T., 106

Reich, R., 493, 498

Reichardt, L., 391, 392, 399

Reinagel, P., 343

Reiter, H., 417

Rempel-Clower, N. L., 336, 363

Renner, P., 133

Resnik, J., 131, 132, 133

Reuter, H., 497, 500, 501, 502

Rey-Barras, A., 188

Ribak, C., 459

Ricardo, J., 445

Riddle, D., 294

Rimbaud, A., 230

Rink, T. J., 497

Risold, P., 449

Ritchie, J. M., 205, 508

Robbins, T. W., 1, 11, 12, 15, 16, 17, 18, 19, 20, 23, 24, 25, 26, 27, 32, 39, 40, 251

Roberts, A., 17

Robertson, D., 190

Robins, E., 432

Robinson, G. A., 196

Robinson, T., 24

Robledo, P., 20

Rodin, A., 80

Roepstorff, A., 83

Roeseler, W., 483

Rogers, J., 205

Rolls, E. T., 237, 238, 244

Romer, A., 429

Rootenberg, B., 458

Roseman, S., 112, 113, 115, 126

Rosenberg, E., 522

Rosenberg, L., 509

Rosenberg, R., 517

Rosenfeld, G., 440, 441, 442, 447

Rosenthal, J., 282

Roska, T., 66

Ross, D., 306

Roth, B., 209

Rougier, O., 473

Rovainen, C., 284

Rubenstein, J., 409

Rubin, L., 294

Ruff, N., 418

Rumelhart, D., 344

Ruminot, I., 204

Rungratsameetaweemana, N., 357

Rushton, W., 494

Rushworth, M., 238

Ruthazer, E., 397, 398, 417

Rutter, M., 87

Ryan, T., 511, 513

Ryder, S., 479, 481

Ryle, G., 344

Sachs, C., 7

Safa, P., 520

Safar, T., 205

Sahakian, B., 17

Sakai, K., 236, 242, 251, 252, 253

Sakmann, B., 281, 286, 501

Salomon, F., 426

Saltz, J., 458

Sanchez-Watts, G., 444, 446

Sanchez-Watts, K., 444

Sanders, J. K., 329

Sanes, J., 119, 291

Saper, C., 433, 435, 436, 456, 457

Sapiurka, M., 343

Sappho, 186

Sarter, M., 17

Sather, W., 503, 504, 512, 517

Sato, M., 418

Sawchenko, P., 437, 438, 439, 440, 441

Scarpa, A., 182

Schaad, N., 203

Schachner, M., 403

Schacter, D. L., 245, 254, 349

Schally, A., 195, 438

Schapiro, M. O., 459

Scheller, R., 510, 511

Schiller, P., 327, 383, 384, 385, 386, 389, 390, 417

Schmidt, F., 479

Schmidt, J., 479

Schmidt-Kastner, R., 61

Schmolck, H., 363

Schmoll genannt Eisenwerth, J. A., 80

Schneider, M., 507

Schoppman, A., 393, 418

Schorderet, M., 191, 192, 193, 202, 203, 500

Schramm, M. J., 38

Schubert, F., 231

Schulman, H., 121, 159, 507

Schulteis, G., 359

Schuman, E., 511

Schuz, A., 208

Schwartz, D., 306

Schwartz, E., 106, 119

Schwartz, J. C., 33, 127, 129, 195, 196

Schwartz, R., 13

Schwarz, J., 168, 169

Schwarz, T., 510, 512

Schweizer, F., 517

Scoville, W. B., 238, 336

Scruton, D., 4

Searle, E., 131, 132, 133

Seeburg, P., 63, 105, 106, 134

Segal, D. S., 328

Sejnowski, T., 106

Sekihara, K., 253

Selden, N., 23

Senju, A., 93

Setsuie, R., 235

Shah, A., 88, 89

Shahabi, C., 452

Shallice, T., 86, 92, 95, 245

Shammah-Lagnado, S., 456

Shankweiler, D., 85

Shapiro, L., 509

Shapiro, M., 81

Sharbaugh, A., 484

Sharpe, T., 431, 432

Sharpee, T., 418

Shatz, C., 150, 156, 361, 390, 391, 398, 399, 405, 407

Shem, S., 491, 492

Shen, T. H., 478

Shepherd, G. M., 250

Sherk, H., 387, 388

Sherrington, C. S., 234, 297

Shiang, J., 473, 477, 484, 495, 499, 502, 509, 514, 515

Shields, W. E., 254

Shimamura, A. P., 245, 363

Shin, W., 513

Shippenberg, T., 31

Shiu ‘Er, H., 311

Shoemaker, W., 194

Shokat, K., 406

Shonkoff, J., 161, 162

Shooter, E., 150, 151, 510

Shoten, I., 232

Shoten, Y., 232

Shrager, Y., 343, 363

Shuz, A., 213

Sidtis, J. J., 246

Siegelbaum, S. A., 501, 516

Siekevitz, P., 122, 124, 134

Siggins, G., 194, 195, 197, 205

Sigworth, F., 507

Sík, A., 63

Silver, M. A., 418

Simerly, R., 442

Simmel, M., 93

Simmons, D. M., 439, 441, 446

Simmons, R. M., 496

Simpson, J. I., 233

Singer, W., 403, 405

Singleton, V., 3

Sironi, P. G., 181

Slater, P. C., 330, 332

Small, S. A., 456

Smirnov, V., 231

Smith, A. D., 56, 57, 58, 61

Smith, C., 334, 347, 355, 359, 363

Smith, J. D., 254

Smith, S. M., 482, 510, 519

Smolover, M., 499

Snowling, M., 83, 85

Snutch, T., 511, 512

Snyder, D., 475

Snyder, S., 191, 441

Sodian, B., 92

Soeter, M., 38

Söhn, F., 458

Sokoloff, L., 207, 210, 390

Sokoloff, P., 33

Solomon, F., 125

Soltesz, I., 59, 63

Sommer, M. A., 257

Somogyi, P., 55, 56, 58, 59, 61, 63, 67

Song, Z., 355, 363

Sotelo, C., 198

Southwell, D., 409

Spanis, C. W., 331

Spemann, H., 288

Spencer, H., 361

Sperlágh, B., 65

Sperry, R., 246, 286, 383, 406

Spiteri, N., 447

Sporns, O., 453, 454, 455, 456

Sprague, J., 383

Spruston, N., 106

Spudich, J., 509

Squire, Caroline, 361

Squire, Charlie, 361

Squire, L. R., 40, 180, 238, 243, 244, 251, 323, 324, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 338, 339, 341, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 354, 356, 357, 522

Squire, Luke, 361

Squire, R., 361

Squire, T., 522

Srebro, B., 457

Sridharan, D., 167, 168

Stacey, P., 14

Stanfield, B., 437

Stanfield, E., 11

Stark, C. E. L., 351, 354, 363

Stefanacci, L., 336

Stein, D., 489, 496

Steinbach, J. H., 502

Stella, N., 208

Stellar, E., 450

Stellwagen, D., 405

Sterling, J., 12

Stern, C., 237

Stevens, C. F., 400, 457, 495, 502, 507, 508, 509

Stevens, F., 457

Stevens, J., 502

Stevens, M., 502

Stevenson, A., 377

Stewart, L., 95

Stocker, J., 519

Stone, S., 460

Straub, R., 204, 205, 206

Strauss, J., 128

Streep, M., 499

Stricker, C., 512

Stryker, B., 416

Stryker, E., 416

Stryker, G. B., 374

Stryker, James, 416

Stryker, Jenny M., 416

Stryker, Matthew, 416

Stryker, Michael P., 373, 374, 384, 387, 388, 390, 391, 393, 394, 395, 396, 397, 398, 399, 401, 402, 403, 405, 409, 410, 411

Stuart, A., 118

Stuss, D. T., 245

Südhof, T., 511

Sun, S., 522

Sun, Y. J., 418

Sunderarajan, J., 311

Sung, K., 304, 305

Surrey, J., 492

Sutherland, E., 195, 196

Suutari, B., 522

Suzuki, A., 210, 212, 363

Suzuki, W., 339, 340

Swanson, B., 426

Swanson, D., 427

Swanson, H., 427

Swanson, L. W., 15, 425, 426, 432, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459

Swanson, Lee, 460

Swanson, M., 427

Swanson, N., 430, 437, 438, 444, 445, 446, 457, 458, 460

Swanson, Raymond, 207

Swanson, Reid, 437, 460

Swanson, S., 426

Swanson, T., 427, 428

Sweet, W., 276, 277, 279

Szentágothai, J., 53, 55, 57, 59, 62, 67

Szo˝nyi, A., 64

Tadi, M., 210

Tadross, M., 513, 521

Taha, S., 418

Takahashi, S., 210, 512

Takeda, M., 248, 249, 250

Takeuchi, D., 248, 249, 250

Tallandini-Shallice, M., 95

Tamura, K., 244, 248

Tanabe, T., 517

Tanaka, K., 249, 402

Tang, Y., 409

Tank, D., 410

Tantam, D., 94

Tasaki, I., 473, 507

Tauffenberger, A., 213

Taylor, J., 15

Taylor, R. E., 496

Teng, E., 343, 348, 363

Terry, C., 70

Teuber, H., 327, 417

Thatcher, M., 489

Therianos, S., 209

Thiagarajan, T., 520

Thoenen, H., 6

Thomas, K., 34, 35

Thomas, R., 494

Thompson, M., 458

Thompson, R. F., 429, 446, 448, 453

Thucydides, 482

Tijan, R., 514

Tirko, N., 521

Toga, A., 449, 452

Tokuyama, W., 250

Tomita, H., 247

Tonegawa, S., 258, 259

Tongroach, P., 233

Tononi, G., 453

Torrealba, F., 399

Tosteson, D., 189, 190, 508

Tóth, K., 61, 63, 64

Toyama, K., 234, 239

Trachtenberg, J., 401, 418

Trafton, C., 429, 430

Tran The, J., 217

Trautwein, W., 489

Trepel, C., 418

Triplett, J. W., 408

Trump, D., 473

Tsao, D., 257, 402

Tse, D., 343

Tsien, A., 514

Tsien, G., 514

Tsien, H. C., 478

Tsien, H. S., 478

Tsien, J., 473, 477, 484, 495, 499, 502, 509, 514, 515

Tsien, L., 481, 496

Tsien, Richard W., 471, 472, 488, 490, 492, 495, 496, 497, 499, 500, 501, 502, 504, 506, 507, 512, 513

Tsien, Roger, 474, 478, 480, 481, 496, 497, 509

Tsien, S., 480, 502, 514

Tsien, Y., 476

Tulving, E., 245, 336, 345, 349

Tye, K., 19

Tylen, K., 83

Tyler, C. W., 405

Udenfriend, S., 435

Ullman, S., 244

Ungerstedt, U., 7, 8, 9

Updike, J., 491

Urgolites, Z. J., 347, 357, 358, 363

Ursin, H., 457

Vagelos, R., 432

Vale, W., 195, 438, 442

van Breemen, C., 505

Van Essen, D., 123, 129, 150, 289

van Winden, S., 169

Vandeffel, W., 256

Vanderschuren, L., 28

Varga, V., 63, 64

Varon, S., 202

Vereecke, J., 503

Verlaine, P., 230

Vertes, R., 456

Vezzoli, E., 211

Vielmetter, J., 106

Vielmetter, S., 106

Vizi, E. S., 61, 62, 65, 66

Vokurka, B., 477

Volkow, N., 27

von Bingen, H., 77

von der Malsberg, C., 244

Von Karman, T., 478

Voutsinos-Porche, B., 210

Vukán, G., 70

Wade, N., 438

Wadleigh, K., 483

Wagner, A, D., 242, 245

Wagner, H. J., 191

Wais, P. E., 355, 363

Waitzman, D., 418

Walken, C., 499

Walls, A. B., 210

Wang, H. G., 513

Wang, X., 522

Warburg, O., 208

Warren, D., 446, 460

Warrington, E., 86, 92, 329, 349

Waterhouse, L., 85

Waters, J., 484

Watson, J., 57, 451, 452, 453, 473, 474

Watts, A., 444, 446

Weber, B., 210

Weber, M., 231, 259

Weed, E., 83

Weidmann, S., 498, 501

Weidmann, W., 473

Weingart, R., 500, 516

Weis, W., 510

Weiskrantz, L., 18, 237, 349

Weiss, T., 486

Wesley, E., 99

West, A., 460

Westergard, C., 458

Westrum, W., 362

Wetzel, D., 363

Wexler, N., 106

Wheeler, D., 512, 513, 518, 521

Wheeler, K., 70, 245

Wheeler, M. E., 242

White, L., 296

Whitelaw, R. B., 26

Whitlock, D. G., 459

Whitteridge, D., 60, 493

Wickwire, C., 114, 116, 117

Wiederholt, M., 486

Wiener, N., 451

Wiesel, M., 190, 239

Wiesel, T., 118, 119, 190, 214, 272, 277, 278, 284, 295, 385, 388, 389, 390, 391, 392, 397, 404, 443, 493

Wilde, O., 230

Williams, E., 487

Williams, M., 298, 299

Williams, S., 309

Williamson, A. V., 504

Willuhn, I., 29

Wilson, H., 9

Wimmer, H., 91

Wing, L., 91, 94

Winkowski, D., 163, 164

Wise, R., 26

Witten, I., 162, 163

Wixted, J. T., 238, 353, 354, 355, 356

Wojtach, B., 304, 305, 316

Wold, B., 106

Wolfe, L., 208

Wong, R., 407

Woodruff, G., 91

Wooldridge, D., 276

Woolsey, T., 437, 457

Wu, G., 520

Wu, J., 503

Wurtz, R., 384, 385, 431

Xue, Y. X., 38

Yan, N., 503

Yang, J., 212, 503, 517

Yang, N., 519

Yang, Z., 301, 302

Yarom, Y., 506

Yeggapan, C., 316

Yellen, G., 502

York, M., 460

Yoshida, M., 250

Yoshikami, D., 506, 512

Young, A., 106

Young, B., 426

Young, M., 451

Young, P. T., 429

Yu, N., 208

Yue, D. T., 503, 504

Zahs, K., 397, 417

Zapata, A., 31

Zarubchik, J., 473

Zemel, R., 302

Zerarka, S., 209

Zhang, F., 497

Zhang, J., 497, 503, 517

Zhang, Q., 513, 521

Zhao, Y., 503, 512

Zheng, W., 158

Zhuo, M., 519

Ziauddeen, H., 34

Zinn, K., 106

Zola-Morgan, S., 323, 334, 336, 337, 338, 339, 340, 341, 342, 345, 348, 360

Zouzounis, J., 360

Zucker, S., 412

Zuckerman, S., 4