Among the symptoms experienced by people who develop post-traumatic stress disorder (PTSD) are symptoms of “anxious arousal”––feeling tense or easily startled much of the time. New research published in the April issue of the journal JAMA Psychiatry links these symptoms to a reduction in the size of the amygdala, a structure deep in the brain that is associated with fear processing and emotion.

Understanding the relationship between structural changes in the brain and PTSD could help researchers develop better approaches for preventing and treating the disorder. Previous studies have shown that another brain structure, the hippocampus, is smaller in people with PTSD than in those without the disorder. But despite the amygdala's role in fear processing and its suspected involvement in PTSD, no clear relationship has been established between the size of the amygdala and the disorder. Studies comparing the size of the amygdala in people with PTSD to its size in unaffected individuals have yielded conflicting results.

A team of scientists led by Robert H. Pietrzak, Ph.D., of the Department of Veterans Affairs National Center for Posttraumatic Stress Disorder (NCPTSD) in Connecticut, decided to consider the amygdala's relationship to PTSD in a more nuanced way. Because not all people with PTSD have the same symptoms or experience their symptoms with the same severity, the scientists wanted to evaluate whether amygdala size correlates to certain clusters of symptoms, rather than the overall disorder.  

The team included Foundation Scientific Council member and three-time NARSAD grantee John Krystal, M.D., at the Yale University School of Medicine (2000, 2006 Distinguished Investigator); Alexander Neumeister, M.D. (2007 Independent Investigator) at the NYU School of Medicine; and Chadi Abdallah, M.D. (2012, 2014 Young Investigator), also at Yale.  Drs. Krystal and Chadi are also affiliated with NCPTSD.

The researchers used magnetic resonance imaging to assess the size of the hippocampus and the amygdala in 48 combat veterans who served in Iraq or Afghanistan. Twenty-three of the veterans in the study had been diagnosed with PTSD. There are two of each of these structures in the brain––one on the right side, one on the left––and each was measured individually.

For each patient, the team correlated the size of the amygdala and hippocampus to the severity of each of five categories of symptoms: anxious arousal; dysphoric arousal (sleep difficulties); re-experiencing (through dreams, flashbacks, or frightening thoughts); avoidance (of reminders of the traumatic event); and emotional numbness.

The researchers found one significant correlation: in veterans with the most severe anxious arousal symptoms, the right amygdala was smaller than it was in other study participants. They also found that the right amygdala was smallest in veterans who had been exposed to the most severe combat.

The scientists say their findings suggest that combat exposure may contribute to shrinking of the amygdala, which is in turn associated with increased anxious arousal.

Read the abstract.