Word: hippocampus
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Memories of concrete facts and events, which can in principle be retrieved on demand, are coordinated through the hippocampus, a crescent-shaped collection of neurons deep in the core of the brain. Other sorts of memory are handled by other areas. The amygdala, for example, an almond-size knot of nerve cells located close to the brain stem, specializes in memories of fear; the basal ganglia, clumps of gray matter within both cerebral hemispheres, handle habits and physical skills; the cerebellum, at the base of the brain, governs conditioned learning (as when Pavlov's dogs salivated at the ringing...
Damage to any one of these regions has an effect on the corresponding form of memory. A much studied patient known as HM, for example, lost much of his hippocampus in the course of surgery to relieve severe epilepsy. As a result, he could remember everything that happened to him before the surgery, but he was completely unable to form new memories. He was stuck forever in the 1950s. Yet HM was able to learn new skills, such as drawing while looking in a mirror...
Just how estrogen works in the brain remains obscure, though research by Bruce McEwen at Rockefeller University has shown that the hormone increases the number of connections between nerve cells in the hippocampus, a region that helps govern memory. Estrogen also increases the production of acetylcholine, a brain chemical that is abnormally low in Alzheimer's patients...
...Illinois at Urbana-Champaign. She points out, for instance, that mother rats lick their male offspring more frequently than they do their daughters. However, Juraska has demonstrated that it is possible to reverse some inequities by manipulating environmental factors. Female rats have fewer nerve connections than males into the hippocampus, a brain region associated with spatial relations and memory. But when Juraska "enriched" the cages of the females with stimulating toys, the females developed more of these neuronal connections. "Hormones do affect things -- it's crazy to deny that," says the researcher. "But there's no telling which...
...other, more momentous events make a biochemical impression in the brain, specifically in a middle portion known as the hippocampus. To file them away permanently, the hippocampus shunts the elements of the experience -- the sounds, smells and sights -- through a network of nerve cells to different areas of the brain. "It's a whole cascade of processes, physiological and chemical, that sensitizes the neurons to transmit messages," notes Mortimer Mishkin, chief of the neuropsychology laboratory of the National Institutes of Health. The proper stimulus, say, a whiff of a perfume or a glimpse of a familiar place, trips the relay...