In a really fascinating and important meta-analysis, researchers from Tufts University studied identical twins to see whether resting functional brain abnormalities found in combat-related PTSD are acquired characteristics or familial risk factors.

Recent neuroimaging research has shown functional abnormalities in the anterior cingulate cortex, amygdala, and hippocampus in people with posttraumatic stress disorder (PTSD).

This study compares the PET scans (of resting regional cerebral metabolic rate for glucose) in fourteen combat-exposed veterans with PTSD and their fourteen identical co-twins, not exposed to combat, as well as nineteen combat-exposed veterans without PTSD (n = 19) and their nineteen identical co-twins, not exposed to combat.

Veterans with PTSD and their co-twins had significantly higher resting rCMRglu in the dorsal anterior cingulate cortex/midcingulate cortex (dACC/MCC) compared with veterans without PTSD and their co-twins. Resting rCMRglu in the dACC/MCC in unexposed co-twins was positively correlated with combat exposure severity, PTSD symptom severity, and alcohol use in their exposed twins.
The study concludes that enhanced resting metabolic activity in the dACC/MCC appears to represent a familial risk factor for developing PTSD after exposure to psychological trauma.

Citation:  Shin LM, Lasko NB, Macklin ML, Karpf RD, Milad MR, Orr SP, Goetz JM, Fischman AJ, Rauch SL, Pitman RK.  Resting metabolic activity in the cingulate cortex and vulnerability to posttraumatic stress disorder  Archives of General Psychiatry. 2009 Oct; 66 (10): pp. 1099-107 [email protected]