Studies of Gulf War veterans and other soldiers have taught us a lot about PTSD (post-traumatic stress disorder). We know that extreme stress from combat can cause long-term problems affecting a victim's memories and ability to learn. We are less certain why some people develop PTSD and others don't.

Now a new study of Vietnam veterans suggests that combat veterans with higher IQs may be less likely to develop PTSD. These results are surprising because previous studies have not found a strong link between PTSD and areas of the brain that are directly involved with intelligence.

The same study also confirmed that Vietnam veterans with PTSD, whatever their intellectual resources, have more problems with attention, working memory and new learning than veterans without PTSD.

Called "shell shock" during World War I and "battle fatigue" during World War II, PTSD is a distressing, even disabling anxiety disorder provoked by exposure to extreme psychological trauma such as combat, torture, abuse or natural disaster. It causes re-experiencing of the trauma in the form of nightmares and flashbacks, emotional numbing, sleep disturbance and exaggerated startle response. According to the National Vietnam Veterans Readjustment Study, 30.9 percent of male Vietnam veterans and 26.9 percent of female Vietnam veterans have suffered from PTSD at some point in their lives. In the general population, the lifetime prevalence of PTSD has been estimated at anywhere between one and 14 percent.

Jennifer J. Vasterling, Ph.D., of the Veterans Affairs Medical Center in New Orleans, Tulane University School of Medicine and Louisiana State University School of Medicine, led a six-person team that compared the pre-Vietnam intellectual resources of 26 combat veterans with post-traumatic stress disorder (PTSD) and 21 combat veterans without mental disorders. In addition, they measured recorded level of combat exposure and education completed prior to Vietnam service. For PTSD veterans, they also evaluated the severity of the disorder.

The researchers found that although the extent of combat in Vietnam was the most important predictor of PTSD severity, high premilitary IQ appeared to help buffer the vets from developing PTSD. In other words, veterans with greater intellectual resources were significantly less likely to have PTSD. In veterans that developed PTSD, greater intellectual resources were associated with less-severe symptoms.

The authors speculate that intellectual sophistication may protect against PTSD in a variety of ways. Greater verbal skills may help soldiers, says Vasterling, to "'talk out' and make sense of their experience." Verbal skills may help them establish more elaborate networks for social support. Also, greater intellectual resources prior to combat may reflect a hardier, more stress-resistant brain. The study was published in the January 2002 issue of Neuropsychology, a journal of the American Psychological Association (APA).

Asked for his take on this study, TheDoctor's stress expert, Dr. Bruce McEwen, Alfred E. Mirsky Professor and Head of Rockefeller University's Harold and Margaret Milliken Hatch Laboratory of Endocrinology, said: "The authors have done a good job of controlling for as many variables as they could. However, it is not clear to me whether the non-PTSD group really had the same degree of combat exposure as the PTSD victims. Another question is cognitive function and IQ before Vietnam. Lacking actual tests or other hard information on premilitary intellectual functioning, the authors of the study had to rely on 'estimated premilitary IQ,' whose accuracy could be questioned."

"As for the study's finding that PTSD affected combat veterans in similar ways, regardless of intelligence," Dr. McEwen added, "this is consistent with what we have learned from brain imaging that shows shrinkage of the hippocampus and other physical changes in certain areas of the brain."