From the article, they have objective evidence from studying the brains of deceased servicemembers: "It was not chronic traumatic encephalopathy, or C.T.E., wh

From the article, they have objective evidence from studying the brains of deceased servicemembers: "It was not chronic traumatic encephalopathy, or C.T.E., which is found in football players and other athletes who have been repeatedly hit in the head. It was something new. The lab’s research team started looking for similar damage in other brains. In civilians’ brains, they did not find it. Nor was it in the brains of veterans who had been exposed to a single powerful explosion like a roadside bomb. But in veterans exposed repeatedly to blasts, they found it again and again."