Studies about human brain

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COMMENT: Robert Sapolsky, Biological Sciences (415) 723-2649

New studies of human brains show stress may shrink neurons

STANFORD - The first direct evidence that stress can shrink a crucial part of the human brain is being compiled by scientists using new, high-resolution magnetic resonance imaging (MRI) scans, according to a Stanford expert on stress and the brain.

In a review article in the Aug. 9 edition of the journal Science, biological sciences Professor Robert Sapolsky said that the work of several research groups shows links between long-term stressful life experiences, long-term exposure to hormones produced during stress, and shrinking of the part of the brain involved in some types of memory and learning.

Sapolsky studies the effects of stress and stress hormones on wild baboons in Africa and on rats in his Stanford laboratory. He is the author of a popular book, Why Zebras Don't Get Ulcers, on the physiology of the stress response. He said that for 20 years, he and other stress physiologists have wished for a direct way to study the effects of stress on the human brain.

Research by Sapolsky and others has shown that some of those hormones, called glucocorticoids, spell bad news when brain cells are exposed to them for a long time ­ at least in the brains of rats.

Glucocorticoids can cause rats' brain cells to shrivel, as the dendrite branches that they use to communicate with other neurons wither away. Prolonged exposure can kill the neurons or make them vulnerable to destruction during a brain injury or stroke.

The researchers also know that long-term exposure to stress hormones is a fact of life for some animals. Studying a troop of wild baboons, Sapolsky has shown that the same glucocorticoids that flood the bloodstream during a stressful event remain at high levels for months or years if the baboon has a stressful life ­ for example, if he's always in fear of an attack by the dominant male in his troop.

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How many bones are in the human body? Babies are born with 300 bones but by the time they reach adulthood, they have 206 bones.

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