This study had quite a bit to offer when it came to understanding the implantation that PTSD has on the brain. It seem that the in people that had survived a trauma the volume of gray matter in the brain correlates negatively with the CAPS, or  Clinician-Administered PTSD Scale. This means that their score, which indicates increasing severity of symptom expression, is shown to increase as their gray matter decreases. This article provides insight into which parts of the brain are associated with PTSD  and how MRI can serve to aid in study and diagnosis.

Link: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0048298