Yielding a possible clue to what causes post-traumatic stress disorder, a study of Vietnam veterans found that a particular brain structure was smaller in men with more combat exposure.
The size difference was seen in the hippocampus, a part of the brain involved in memory and some other functions.
It might be involved in holding emotional reactions to traumatic experiences in check, said researcher Dr. Roger Pitman. An impairment in the hippocampus might help explain why people with post-traumatic stress disorder can be overwhelmed by memories of stressful events, he said.
Pitman, a researcher at the Veterans Affairs Medical Center in Manchester, N.H., and Harvard Medical School, described the study Tuesday at the annual meeting of the American Psychiatric Association.
The new study used brain scanning to compare the size of the hippocampus in seven Vietnam veterans with PTSD and seven others without it. The degree of exposure to combat was measured by a standard scale that included such factors as how often a person was fired at, saw a buddy killed, was in danger and had other wartime experiences.
The study found that the higher the combat exposure, the smaller the volume of the two hippocampi.
Animal studies also suggest stress can damage the hippocampus.
But Pitman stressed the new study shows only a statistical relationship and does not prove that combat stress shrank the hippocampus.