PTSD, or posttraumatic stress disorder, is a severe anxiety disorder following a traumatic event. Symptoms can include flashbacks, nightmares, emotional instability and uncontrollable thoughts about the event. Xiaodan Yan, a research fellow at NYU School of Medicine, used fMRI (functional magnetic resonance imaging) to measure blood-oxygen levels in the brain of 104 combat veterans from the Iraq and Afghanistan wars. The study evaluated “spontaneous” or “resting” activity in their brains. Yan and colleagues reported that there was spontaneous brain activity in the amygdala, deep in the temporal lobes, involved with emotional responsiveness—the activity was significantly higher in the 52 combat veterans with PTSD as compared with brain activity in the 52 combat veterans without PTSD. The fMRI studies also showed decreased spontaneous activity in the thalamus and dorsal lateral prefrontal cortex. This showed that spontaneous brain activity arises in the brains of those with combat related PTSD even when their brains are at rest.