Brain scans of people with post-traumatic stress disorder (PTSD) have shown abnormalities in parts of the brain called the anterior cingulate cortex, the amygdala and the hippocampus but it is not known whether these abnormalities have developed because of the PTSD or if they reflect an inherited risk factor for the condition. A team of researchers from Massachusetts and New Hampshire investigated this issue in a study of 66 people. All the participants in the study were identical twins and they were divided into two groups. One group was made up of pairs of twins where one twin had fought in a war and developed PTSD and the other twin had not fought. The other group was made up of one twin who had fought but not developed PTSD and their twins who had not fought. Those veterans who had developed PTSD and their non-combatant twins both showed more activity in their dorsal anterior cingulate cortex and their midcingulate cortex than the group of twins who had not developed PTSD after combat and their twins. The more active the brain regions were in the twins not exposed to combat whose siblings had developed PTSD the worse their siblings' PTSD symptoms were. The study shows that enhanced activity in this part of the brain is a risk factor for PTSD, not a consequence of it.
Shin, Lisa M. ... [et al] - Resting metabolic activity in the cingulate cortex and vulnerability to posttraumatic stress disorder Archives of General Psychiatry October 2009, 66(10), 1099-1107