Warren has trouble remembering a lot of things. Which isn't surprising, considering that several pieces of shrapnel tore through his skull after insurgents outside Kandahar blew up his truck with a rocket-propelled grenade in May.
Since 2000, traumatic brain injury, or TBI, has been diagnosed in about 180,000 service members, the Pentagon says. But some advocates for patients say hundreds, if not thousands, more have suffered undiagnosed brain injuries. A Rand study in 2008 estimated the total number of service members with TBI to be about 320,000.
A small percentage of those injuries are as serious as Warren's. To let his brain swell and keep the blood flowing, thereby preventing the damage from worsening, doctors removed virtually the entire left side of his skull, a procedure known as a craniectomy.
Warren's physical wounds will heal, but three weeks after he was hit, military doctors are still discovering the extent of the damage.
Williamson plows ahead with other tests, revealing that Warren doesn't know where he is. "This is the U.S.A.?" he says. Warren cannot subtract seven from 135, but he can spell "world" - though not backward. He can recite the days of the week but can't come up with the words for necktie or button.