We hear a lot about PTSD these days, and with good reason. As more people confront trauma and come away with severely debilitating disorders, it becomes that much more important to understand the mechanism, in order to find ways to treat or prevent it. And one of the ways people are seeking to understand PTSD is by trying to find genetic risk factors for the disorder, in the hope that familial traits will be able to predict who might develop PTSD and who might not, allowing for preventative treatments before exposure, and better treatments after trauma.
And if you're going to study familial components in humans, one of the best ways to do that is to study twins.
VanElzakker, et al. "Preliminary findings of neural responses to fearful facial expression in PTSD from an ongoing study of combat-discordant monozygotic twins" 795.04, II2.
For this study, the authors are looking at two different groups of twins (the study is still ongoing) recruited from the Vietnam Era Twin Registry. In the first group of twins, one twin fought in the Vietnam war and got PTSD, the other twin didn't fight. In the second group of twins, one twin fought in Vietnam and did NOT get PTSD, and the other twin did not fight.
They took these groups of twins and put them in fMRI, where they exposed them to sets of fearful or non-fearful faces. Fearful faces can provoke a response from the amygdala, an area of the brain associated with processing emotions such as fear. People with PTSD are known to have differences in amygdala responses, and this study wanted to confirm this, as well as examining their twins, to see if there was any indication in twins who had not been exposed to combat.
They first checked to see how people subjectively responded to the faces, whether they saw fearful faces as negative and happy faces as positive. There were no differences here. The differences arose only in the fMRI scans. In the fMRI, combat veterens with PTSD showed decreases in prefrontal and cingulate cortex activation patterns compared to vets without PTSD. But what is interesting is that their non-combat exposed twins ALSO showed these changes, showing reduced activation patterns to fearful faces, while non-combat exposed twins who's brothers did NOT have PTSD looked just like their non-PTSD brothers.
This pattern was reversed in the amygdala, where vets without PTSD and their twins showed decreases in activity (increases in prefrontal cortex activity are negatively correlated with amygdala activity, these two areas regulate each other). Vets WITH PTSD and their twins showed an increase in amygdala activation. What it ends up looking like is that vets with PTSD, AND their twins, have a failure to activate structures in the prefrontal cortex in response to fearful faces, and this change results in increased response in the amygdala. And because this effect was also seen in their non-combat exposed twins, this may mean that this activation pattern is a risk factor for PTSD, NOT a result of PTSD.
Of course these results are very preliminary (they are only halfway through the study after all). But if the findings continue in this pattern, it will help scientists to understand risk factors for PTSD that may exist long before people become exposed to traumatic situations, and give them the ability to try and intervene while they still can.