Figure 2.1. Side view of the brain; Image courtesy of the National Institute on Aging/ National Institutes of Health

Amygdala
The amygdala is comprised of a pair of almond-shaped structures—the amygdalae—located on each side of the brain (see figure 2.1). The amygdala plays a key role in the regulation of traumatic memories and of general emotional processing. It's involved in fear conditioning, a term that refers to the process by which fear is triggered by events around us. ­Post-traumatic changes in the amygdala may account for the hypervigilance associated with PTSD.2