“It's sometimes difficult for researchers to know whether PTSD has caused physical changes in the brain, or whether those physical characteristics were already there. Dr. Shaili Jain, a PTSD expert and author of The Unspeakable Mind, explains that there are three main areas of the brain implicated in PTSD: the hippocampus, the frontal lobe, and the amygdala. The hippocampus, she explains, ‘is a part of the brain that's located in the temporal lobe where we process memories. It's smaller in people who have PTSD, but we don't know why.’ It's a case of chicken and egg, she notes: ‘We don't know if they were born with a smaller hippocampus and that somehow made them more vulnerable to PTSD, or if it shrunk after they were exposed to trauma.’”