July 15, 2005

"We've always wondered why some people who are exposed to traumatic experiences go on to develop anxiety disorders like post-traumatic stress disorder and others do not,"
- Mohammed Milad, PhD

Size of brain structure could signal vulnerability to anxiety disorders

The size of a structure in the brain may be associated with the ability to recover emotionally from traumatic events. A new study by MGH researchers finds that area is thicker in individuals who appear better able to modify their anxious response to memories of discomfort. The study has received early online release on the Proceedings of the National Academy of Science website.

"We've always wondered why some people who are exposed to traumatic experiences go on to develop anxiety disorders like post-traumatic stress disorder (PTSD) and others do not," says Mohammed Milad, PhD, a research fellow in the MGH Department of Psychiatry and the study's lead author. "We think this study provides some potential answers."

It is normal to respond with physical and emotional distress to situations that bring back memories of traumatic events. Such responses usually diminish over time, as those situations are repeated without unpleasant occurrences, but some people continue to respond with what can be overwhelming fear and may develop PTSD. Prior studies in animals have suggested that the ventromedial prefrontal cortex (vmPFC) — an area on the lower surface of the brain — may be involved with the ability to modulate the fearful response.

Volunteers in the current study viewed photos of rooms with either a red or blue light turned on. Early in the study period, a mild electric shock was delivered to their hands right after a lamp with a blue light appeared. They then viewed the photos with no shocks administered. The next day, the volunteers again viewed the photos with no shocks, and measurements of perspiration were taken to gauge anxiety levels. Structural imaging studies of the volunteers brains showed that those participants who appeared to have less anxiety response the second day also had a thicker vmPFC.

"These results suggest that a bigger vmPFC may be protective against anxiety disorders or that a smaller one may be a predisposing factor. But exactly how that might work we just don't know," says Milad. The report's MGH co-authors are senior author Scott Rauch, MD, and Roger Pitman, MD, both of MGH Psychiatry, and Brian Quinn and Bruce Fischl, PhD, both of MGH Radiology.