Individuals who experience military combat endure extreme stress, which can lead to the psychiatric condition of post-traumatic stress disorder (PTSD). PTSD is associated with several abnormalities in brain structure and function, but it has remained unknown whether the abnormalities are caused by the traumatic event, or are pre-existing risk factors that increase the risk of PTSD after a traumatic events occurs.
Researchers measured the gray matter density of the brains of combat-exposed Vietnam veterans and their combat-unexposed identical twins using magnetic resonance imaging (MRI). They found that the gray matter density of the pregenual anterior cingulate cortex, an area of the brain involved in emotional functioning, was reduced in veterans with PTSD, but not in their twins.
This supports the theory that psychological stress actually damages this brain region.