Hundreds of vets have tried out an experimental new treatment that could change how the world addresses mental disorders. Tony didn’t know what to expect when he walked into the Brain Treatment Center in San Diego, California, last spring. The former Navy SEAL only knew that he needed help. His service in Iraq and Afghanistan was taking a heavy toll on his mental and physical wellbeing. He had trouble concentrating, remembering, and was given to explosive bursts of anger. “If somebody cut me off driving, I was ready to kill ’em at the drop of a hat,” he said. And...