Brain scans of combat-exposed Vietnam War veterans showed that certain serious head injuries to certain parts of the brain can prevent soldiers from developing post-traumatic stress disorder (PTSD).

The findings, from the National Institutes of Health (NIH) and the National Naval Medical Centre, suggested that drugs or pacemaker-like devices aimed at dampening activity in these brain regions might be effective treatments for PTSD.

PTSD involves the persistent reliving of a traumatic experience through nightmares and flashbacks that may seem real. Twenty percent to 30 per cent of Vietnam vets (more than 1 million) have been diagnosed with PTSD, and a similar rate has been reported among Hurricane Katrina survivors in New Orleans. Public health officials are currently tracking the disorder among soldiers returning from Iraq. Yet, while war and natural disasters tend to call the greatest attention to PTSD, it's estimated that millions of Americans suffer from it as a result of assault, rape, child abuse, car accidents, and other traumatic events.

Previous studies have shown that PTSD is associated with changes in brain activity, but those studies couldn't determine whether the changes were contributing to the disorder or merely occurring because of it.

Jordan Grafman, Ph.D., a senior investigator at the National Institute of Neurological Disorders and Stroke (NINDS), part of NIH, turned to the Vietnam Head Injury Study (VHIS) to make that distinction. The VHIS is a registry of Vietnam veterans who sustained penetrating brain injuries (which are less common in Iraq compared to concussion brain injuries). It has received support from the Department of Defense, the Department of Veterans of Affairs and NIH, and is currently supported by NINDS.

"If we could show that lesions in a specific brain region eliminated PTSD, we knew we could say that the region is critical to developing the disorder," said Dr. Grafman. The results of his study appear online today in "Nature Neuroscience".

Dr Grafman and members of his lab, including neuropsychiatrist Vanessa Raymont and postdoctoral fellow Michael Koenigs, studied 193 veterans registered with VHIS and 52 veterans with combat exposure but no head injury. The participants were classified as either having developed PTSD at some point in their lifetime or having never developed PTSD. CT (computerised tomography) scans were used to map their brain injuries.

By comparing the distribution of brain injuries between the PTSD group and the non-PTSD group, the researchers found two regions where damage was rarely associated with PTSD: the amygdala, a structure important in fear and anxiety, and the ventromedial prefrontal cortex (vmPFC), an area involved in higher mental functions and planning.

In another level of analysis, the researchers compared the prevalence of PTSD in subjects who had damage to either the amygdala or vmPFC, subjects who had damage to other parts of the brain and non-head-injured subjects. PTSD occurred in a similar fraction of subjects in the last two groups 40 per cent and 48 per cent, respectively. In contrast, PTSD occurred in only 18 per cent of subjects with damage to the vmPFC and zero (out of 50) subjects with damage to the amygdala. The occurrence of other anxiety disorders was not affected by damage to the amygdala or vmPFC.

"It appears that if you have damage to either of those areas, you're not likely to develop PTSD," said Dr. Grafman. The scientists hypothesize that drugs designed to inhibit the activity of the two structures might provide relief from PTSD. Deep brain stimulation, a technique used to treat Parkinson's disease by modifying the brain's electrical activity, might also prove useful against PTSD if targeted to the amygdala or vmPFC.

Current treatments for PTSD include medications for anxiety and depression, and therapy to help the person confront and deal with traumatic memories. But these treatments vary in effectiveness, a point underscored by the fact that many of the Vietnam veterans in Dr. Grafman's study are still dealing with PTSD some 40 years after the war.

Since the study examined only young men who served in Vietnam, one question is whether the results will extend to women, children, or people exposed to traumatic situations besides wartime combat. Similar results probably will be found in those other populations, given that previous studies had connected PTSD to changes in the amygdala and vmPFC, and only some of those studies involved war veterans.

NINDS is a component of the National Institutes of Health (NIH), and is the nation's primary supporter of biomedical research on the brain and nervous system.