An Orange Flash
In November 2004, Stephen Kinney, a U.S. National Guard sergeant from North Chelmsford, MA, was patrolling a main supply route through southern Iraq when a buried artillery shell exploded outside the door of his Humvee. The blast propelled the vehicle into the air, riddling the doors with shrapnel. "All I remember is a big orange flash," says Kinney, who was thrown against the Humvee's radio, then against the ceiling, and briefly lost consciousness.

More concerned about a bruised hip and swollen shoulder than about his head, Kinney never considered the possibility of brain injury. The doctor who treated him at a military field hospital in Iraq didn't ask him about losing consciousness, or about his state of mind after the blast. "There were marines coming in from ­Fallujah with their arms blown off," says Kinney. "They figured if you weren't bleeding and had all your limbs, you were doing okay."

It wasn't until months after Kinney's return home the following February that he saw a psychiatrist at the local VA hospital and was evaluated for brain injury. He underwent extensive neuro­psychiatric testing, which assessed cognitive capacities such as memory, attention, and higher-order reasoning, and he was diagnosed with mild traumatic brain injury. When Kinney returned to his job with the post office, he began to notice problems. He had ­trouble remembering names and numbers and often forgot whether he had scanned the bar codes on mailboxes along his route, as mail carriers do every 30 to 60 minutes to log their progress. In addition, though he'd been an avid illustrator (while on duty in Iraq he drew a Christmas card depicting a Humvee parked under a decorated palm tree), he hasn't taken up his colored pencils since he returned.

Despite the designation "mild," even a single concussion can produce serious symptoms, including severe headaches, difficulty sleeping, problems with memory and concentration, and even changes in personality. "The spouses say, 'He is totally different--he used to be a quiet guy and now he's agitated,' or 'He used to be energetic and now has no motivation,'" says Jeffrey Barth, a neuropsychologist at the University of Virginia School of Medicine in Charlottesville who has done pioneering work in the study of concussion. "They can also lose the ability to put everything together and to make good judgments." About half of people who suffer concussions quickly recover. But in the rest, symptoms can linger indefinitely. About 10 percent of concussion victims have problems severe enough to interfere with daily life and work. "No one knows how to treat it, how long it lasts, and whether it's safe to leave someone deployed," says Jon Bowersox, chief of surgery at the Cincinnati VA Medical Center and a colonel in the U.S. Air Force Reserve.

Especially worrying is the prospect that troops in Iraq will suffer repeated concussions, reinjuring their brains while they're still in a vulnerable state. For soldiers patrolling highways and guiding convoys, exposure to multiple blasts is a given; some have reported encountering tens of blasts in a day. In rare cases, multiple concussions in quick succession can lead to serious injury. But subtler damage may also accumulate, leading to depression and cognitive decline. "It's still an open question," says Barth. "How many concussions can you have without having a really bad outcome down the road?"