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STRESS DISORDER TIED TO HIPPOCAMPUS SIZE Study Compared Region of the Brain in Twins By Andrew Bridges, The Associated Press, Reported in Las Vegas Review Journal LOS ANGELES - A study of 80 men, 40 who saw combat in Vietnam and their twins who did not, suggests that the size of a region of the brain involved in storing memories can predict vulnerability to post-traumatic stress disorder. Previous studies have found the region, called the hippocampus, is smaller than normal in the brains of veterans who suffer from the disorder, marked by flashbacks and sometimes overwhelming memories of traumatic experiences. The assumption has been that stress caused the region to shrink in volume. Now, a study that involved 40 sets of identical twins indicates the smaller volume is inherited and not a consequence of the trauma of combat. It suggests the hippocampus can increase one's vulnerability to the syndrome's effects. "That would probably be the most likely explanation of the results," said psychologist Mark Gilbertson of the Veterans Administration Medical Center in Manchester, NH, and co-author of the study, which appeared Tuesday in the electronic edition of the journal Nature Neuroscience. The study was sponsored by the Veterans Administration. Post-traumatic stress disorder has afflicted nearly 31 percent of all Vietnam combat veterans at some time, according to government estimates. In the new study, about half the 40 combat-veteran patients suffered chronic, unremitting post-traumatic stress disorder. The other half had never been affected, nor had the 40 stay-at-home twins. In veterans who were affected, hippocampal volume was 10 percent smaller on average than in those who had never suffered from the syndrome but who had seen combat. Twins of the combat veterans who reported problems also had smaller hippocampi, even though they had seen no combat. Most had served in the armed forces, however; Gilbertson said. Because identical twins have similar brain structures, the finding suggests those veterans suffering from the disorder had smaller hippocampi before they entered combat. Gilbertson cautioned that smaller hippocampus volume did not guarantee a combat veteran would suffer from the syndrome; the severity of combat is a better predictor of the outcome.
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