CONSTANT STRESS MAY BE MORE THAN just nerve-racking. It may kill nerve cells outright, causing a key part of the brain to shrink. Recent studies in rats show that sustained exposure to stress-induced hormones produces permanent damage in the hippocampus, a seahorse-shaped brain structure involved in learning and memory. Now, scientists are finding similar effects in people.

At Washington University in St. Louis, Yvette I. Sheline, an assistant professor of psychiatry, knew that stress hormones such as cortisol are produced during bouts of depression. She wondered whether high levels of the hormones left their stamp on the brain. Using a high-resolution magnetic-resonance scanner, she compared women who had a history of depression with others who did not. She found that the hippocampus was, on average, 12% smaller in women with multiple episodes of depression. Other researchers have discovered similar, small hippocampi in Vietnam vets and child-abuse victims with post-traumatic stress disorder. Sheline admits the smaller hippocampi may be the cause, not the result, of these disorders. But given the animal experiments and new human studies, stress hormones look like bad news for the brain.

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