Science News, Volume 149: Page 315, 18 May 1996.
Bruce Bower reports from New York City at the annual meeting of the American Psychiatric Association
New studies suggest that people who fall prey to a severe stress reaction following military combat or sexual abuse have an unusually small hippocampus, a brain structure that helps to regulate memory. But scientists cannot say whether severe trauma somehow causes the hippocampus to shink or whether a small hippocampus somehow contributes to trauma.
In a brain scan investigation by Murray B. Stein of the University of California, San Diego, 22 women who cited repeated childhood sexual trauma, displayed hippocampus volumes smaller by 5 percent than those of 20 women who reported no sexual abuse and no psychiatric disorders. Similar findings appeared last year (SN: 6/3/95, p.340).
Sixteen of those sexually abused women suffered from post-traumatic stress disorder (PTSD). Hippocampal volume was lowest in those reporting the most severe dissociation, Stein asserts. Dissociation includes feelings of detachment from one's self and other alterations of consciousness.
Women abused as young children performed better on short-term memory tasks than those abused at later ages. The brains of young children may have more resilence to trauma than those of teenagers or adults, Stein theorizes.
Another study conducted by Tamara V. Gurvits of the Veteran Affairs Medical Center in Manchester, N.H., found a 24 percent smaller hippocampus size in seven Vietnam combat veterans suffering from PTSD, compared to seven Vietnam combat veterans free from PTSD and eight men who did not serve in the military. In the PTSD group, the smallest hippocampal volume appeared in those exposed to the most severe combat, Gurvits reports.
Trauma researchers must account, however, for brain scan evidence that healthy people experience a drop in hippocampal volume of about 15 percent as they age, contends Mony J. de Leon of New York University Medical Center.
In a four year study of 405 elderly volunteers, de Leon and his coworkers found that probable cases of Alzheimer's disease often emerge in people who start out with a small hippocampus and mild memory problems. Hippocampal volume declined from 20 percent to 50 percent more in victims of apparent Alzheimer's disease than in healthy elderly controls, according to Leon.
Several possible explanations exist for a link between a smaller hippocampus and PTSD, argues Roger K. Pitman, a New Hampshire colleague of Gurvits. Hippocampal shrinkage may occur first and boost the likelihood either of encountering traumas (such as making one more prone to volunteer for combat) or developing PTSD after trauma. Conversely, hippocampal atrophy may result directly from severe trauma, from PTSD produced by trauma, or from alcohol or illicit drug abuse, which frequently accompanies PTSD.
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