There’s growing evidence that a physical injury to the brain can make people susceptible to post-traumatic stress disorder. Studies of troops who deployed to Iraq and Afghanistan have found that service members who have suffered a concussion or mild TBI are far more likely to develop PTSD, a condition that can cause flashbacks, nightmares and severe anxiety for years after a traumatic event. And research on both people and animals suggests the reason is that a brain injury can disrupt circuits that normally dampen the response to a frightening event. The result is like “driving a car and the brake’s not fully functioning,” says Mingxiong Huang, a biomedical physicist at the University of California, San Diego.
Scientists have suspected a link between traumatic brain injury (TBI) and PTSD for many years. But the evidence was murky until researchers began studying troops returning from Iraq and Afghanistan. Using magnetoencephalography,or MEG, Huang and a team of researchers scanned the brains of 84 people who had experienced a brain injury. Those scans found abnormal signals coming from the brains of people who’d had a concussion. And the location of those abnormal signals suggested that there was too much activity going on in the amygdala and not enough in an area that normally tempers emotional reactions. The result is a brain that is “like a car with no brake,” Huang says.