A car backfires in a parking lot. An army veteran, recently returned from a combat zone, might duck and cover. He knows that he is no longer in an active war zone, but he was trained to react before thinking, an ability that meant life over death at one point in his life. That training is so ingrained it has physically altered the way his brain works, weakening the connection between the amygdala, which is responsible for emotions like fear, and the prefrontal cortex, which regulates or controls these emotional…
