Post-traumatic stress disorder (PTSD) has now emerged from the realm of psychology to the realm of neuroscience and brain structure. In the brain there is a right and a left amygdala that, together, help control emotion, memories, and behavior. Current research suggests that the right amygdala controls fear and reactions to unpleasant stimuli. Researchers at the University of California San Diego studied 89 current or former members of the military with mild traumatic brain injury. Twenty-nine of the subjects had significant PTSD while the other subjects did not. Using brain scans to measure the volume of various brain regions, the researchers found that injured subjects with PTSD had amygdalas, particularly on the right side, that were 6 percent larger than those injured subjects with no PTSD. The research findings are illuminating but further research is needed. Researchers point out that most of the study participants’ injuries were caused by blast injuries, as opposed to, for example, sports-related concussions. In addition, the study shows only an association and does not prove either that PTSD causes structural changes in the amygdala, or vice versa. That said, the study is a breakthough in understanding PTSD and bringing together two major areas of brain study and research.