In the 1950s, a young man with permanent amnesia changed what we know about learning and memory. Henry Molaison, better known as patient H.M., lost the ability to form new conscious memories after undergoing brain surgery to treat his intractable epilepsy. He experienced every aspect of daily life, like eating or taking a walk, as though it were the first time. When he met someone new, he would forget the encounter within a few minutes. By studying him, scientists learned that complex functions such as learning and memory are tied to distinct biological processes and regions of the brain. They learned the brain’s medial temporal lobe, which includes the hippocampus and parahippocampal region, converts short-lived perceptions into long-term memories. The discovery paved the way for further exploration of the brain networks encoding conscious and unconscious memories as well as emotions. Like memory, emotions arise from activity in distinct regions of the brain, primarily a tiny almond-shaped structure called the amygdala, which integrates emotions and motivation.
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