Vol. 9, No. 1, 2003 Page 2
Many soldiers survive violent combat experiences without developing mental problems, while many others suffer from post-traumatic stress syndrome (PTSD) that leaves them psychologically crippled for decades. A new study suggests that while the severity of stress plays a strong role, innate brain vulnerabilities also are a factor in determining who develops PTSD and who does not.
Mark Gilbertson and colleagues performed magnetic resonance imaging scans on 40 Vietnam War veterans, all of whom had identical twin brothers who did not experience combat. Seventeen of the veterans suffered from chronic PTSD.
Comparing veterans with PTSD to those who were mentally healthy, the researchers found that the PTSD group had a hippocampal volume significantly smaller in relation to total brain size. In addition, those with the most severe PTSD had the smallest relative hippocampal volume.
Significantly, the PTSD veterans' twins, who had not been in combat situations and did not have symptoms of PTSD, also had smaller relative hippocampal volumes than twins of psychologically healthy combat vets. The hippocampus is a brain region involved in memory and learned responses to fear.
When Gilbertson et al. refined their results by eliminating data from subjects who had experienced childhood abuse, the differences remained significant, helping to rule out early trauma as a factor in the development of post-war PTSD.
Previous studies also have revealed smaller hippocampal volume in PTSD sufferers than in controls, leading researchers to suggest that chronic high stress levels damage the hippocampus. The findings of Gilbertson et al., however, indicate that many people who develop PTSD are innately vulnerable to the disorder due to biological differences in their brains. Gilbertson notes, however, that the severity of combat experience still is a better predictor of PTSD, and that hippocampal volume is not an accurate marker for the risk of developing PTSD.
"Smaller hippocampal volume predicts pathologic vulnerability to psychological trauma," Mark W. Gilbertson, Martha E. Shenton, Aleksandra Ciszewski, Kiyoto Kasai, Natasha B. Lasko, Scott P. Orr, and Roger K. Pitman, Nature Neuroscience, Vol. 5, November 2002, 1242-7. Address: mark.gilbertson@med.va.gov.