MR Shows Post-Traumatic Stress Disorder Linked to Smaller Brain Area Regulating Fear Response

Recent war veterans who are diagnosed with post-traumatic stress disorder (PTSD) have been found to have a considerably smaller volume in a brain region crucial for regulating responses to fear and anxiety.

The study, led by scientists from Duke University (Durham, NC, USA) and the Durham VA Medical Center, was published November 5, 2012, in the journal Archives of General Psychiatry, for the first time provides clear evidence that smaller amygdala volume is associated with PTSD, regardless of the trauma severity. But it is not clear whether the physiologic disparity was caused by a traumatic event, or whether PTSD develops more easily in individuals who naturally have smaller amygdalas.

“Researchers found 20 years ago that there were changes in volume of the hippocampus associated with PTSD, but the amygdala is more relevant to the disorder,” said Rajendra A. Morey, MD, MS, assistant professor at Duke and lead author of the study. According to Dr. Morey, studies in animals have established the amygdala’s role in regulating fear, anxiety and stress responses, but its effect on human behavior is less well known. “It’s associated with how fear is processed, especially abnormal fear processing. So it makes sense to look at the structure of the amygdala.”

The researchers enrolled 200 combat veterans who served in Afghanistan and Iraq after September 11, 2001; half had PTSD and the other half had been exposed to trauma, but had not developed PTSD. Amygdala and hippocampus volumes were computed from magnetic resonance imaging (MRI) scans of all the participants.

Hippocampus and amygdala volumes were calculated from magnetic resonance imaging (MRI) scans of all the participants. The researchers revealed significant evidence that PTSD among study participants was associated with smaller volume in both the left and right amygdala, and validated earlier research tying the disorder to a smaller left hippocampus. The differences in brain volumes between the two groups were not due to the extent of depression, trauma load, substance abuse, or PTSD severity--features the researchers took into account in their statistical model.

The findings provide new clues into a disorder that strikes nearly 14% of combat veterans serving in Iraq and Afghanistan, according to the US Department of Veterans Affairs. PTSD is also estimated to afflict 6.8% of adults in the general population who have suffered crimes, abuse, and other traumas over their lifetimes. “The next step is to try to figure out whether a smaller amygdala is the consequence of a trauma, or a vulnerability that makes people get PTSD,” Dr. Morey said.

According to Dr. Morey, the study demonstrated that amygdala volume does not appear to be affected by the severity, duration, or frequency of trauma, indicating that such exposures do not cause the amygdala to shrink. As a result, it seems more probable that individuals with significantly smaller amygdala are susceptible to PTSD, but more research is required to confirm that finding.

According to Dr. Morey said he and colleagues are exploring that question, and are intrigued by evidence from their study that suggests people may have a propensity for developing PTSD based on inherently smaller amygdala volume. “This is one piece in a bigger puzzle to understanding why some people develop PTSD and others do not,” Dr. Morey said. “We are getting closer to that answer.”

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