Tools for Behavior
- Published6 Mar 2023
- Author Susan Rojahn
- Source BrainFacts/SfN
Our behaviors are what we as living organisms, do. And peering inside our brains to understand how we do what we do can be illuminating. So to understand how brain function drives behaviors in humans, researchers often turn to animal models.
An eight-inch-long marine slug may not look like a very promising model of brain function, but over the years, the animal known as Aplysia has helped scientists uncover many principles of learning and memory. Aplysia has relatively few neurons (around 10,000, compared to approximately 86 billion in humans), but some of its neurons are large enough to be seen with the naked eye. Aplysia also exhibits simple behaviors that can be modified with training. For example, Aplysia will reflexively withdraw its gill after receiving an electric shock to its tail. It can be trained to withdraw its gill in response to an innocuous touch which, during training, was paired with an electric shock. Scientists have discovered how the timing of training sessions affects learning and have identified proteins and other molecules that strengthen synapses so the neuronal response is greater the next time Aplysia is stimulated. Many of the molecules and processes identified in Aplysia’s learning are also involved in human learning.
The fruit fly Drosophila is also commonly used to study behavior, especially how genes control behavior. For example, variations in a gene called ‘foraging’ determine whether flies tend to roam around as they eat or sit in one place. Flies with mutations in another gene called ‘timeless’ don’t have normal circadian rhythms. Mutations have been identified that affect the full gamut of Drosophila behaviors — from aggression to courtship, as well as learning and memory. Many of the affected genes have correlates in humans.
Addiction presents one of the most pressing challenges in studying human behavior — and researchers are still figuring out how to better understand and treat it. Some lab animals like rats will consume alcohol and drugs even if accompanied by a bitter taste or foot shock. Scientists have uncovered changes in the brains of animals exhibiting such addiction-like behaviors that mirror changes seen in the brains of humans with addiction disorders. Interestingly, some breeds of rats are very likely to exhibit addiction and relapse behaviors while others are more resistant. By comparing the genetics of two breeds of rats with different predispositions to cocaine addiction, scientists identified genes that were differentially turned on or off in the two breeds; the study suggests that these genes, and their epigenetic regulation, play a role in susceptibility to addiction. This type of research helps scientists understand why some people are more prone to addiction or relapse and could suggest ways to identify people at risk.
Behavior is also studied directly in humans. Early mapping of human behaviors to specific brain regions was done by observing personality changes in people who had lost small regions of their brain due to injuries or surgeries. For example, people who have lost their frontal lobe often become inconsiderate and impulsive. Modern imaging techniques also help scientists to pair brain regions with certain behaviors. For example, imaging allows researchers to see certain brain areas “light up” when a person is shown human faces, but not when they see faces of other animals. These techniques are also useful to better understand brain disorders — such as identifying brain regions responsible for auditory hallucinations in schizophrenia.
Adapted from the 8th edition of Brain Facts by Susan Rojahn.
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