In the most common, and simple, form of brain injury, called a concussion, the brain usually regains normal function quickly. When it cannot self-repair, the brain sometimes rewires, routing signals along new channels, across its backup networks of axons. There are limits to this. The brain contains a ?nite number of axons. Brain matter, if it regenerates at all, grows very slowly. Repair takes time, weeks or months or even longer. Rehabilitation seems to work best when it occurs almost simultaneously, spurring the brain to form new connections, and the injured to learn new ways of thinking, acting, living. If rehab doesn't follow soon after injury, recovery is less likely to succeed; it may even become impossible.

Soldiers diagnosed with TBI proceed along separate paths depending on the severity of injury: mild, moderate, or severe. Moderate and severe patients are transferred to one of four special hospitals run by the Department of Veterans Affairs. There they receive long-term care and therapy. Patients with mild TBI may be sent home, back to duty, or, if they need additional rehabilitation, to community-based centers that focus on rebuilding their mental abilities. After nearly a month at Walter Reed, Jason Welsh was sent to Virginia NeuroCare, a small, private clinic in the rich green hills of central Virginia.

It is a Thursday morning in early August, and the merciless wet heat of a Virginia summer hangs over Charlottesville. The city is peaceful, collegiate, home to the University of Virginia, and close to Thomas Jefferson's home at Monticello. In the tangled brush, the overgrown forests, and stubbled fields nearby, tens of thousands died in Civil War battles at Fredericksburg, the Wilderness, and Chancellorsville. To reach Sgt. Jason Welsh, you must steer past them all.

Welsh sits in a small office, still wearing a neck brace, and tries to write a grocery list. An occupational therapist named Joy Sandlin helps him. He chooses food for a week of meals. But Welsh has never lived alone or cooked much for himself. Since his arrival at Virginia NeuroCare, he has lived in a group home with other brain-injured patients, some of them soldiers. His TBI has reduced his ability to focus and remember.

"Jason's going to need to learn to shop for himself and eat healthily," says Sandlin, a petite young woman with long black hair. "One of the things is that he's a 25-year-old guy who moved directly from his mom's house to the Army. He's never had to do this before, and he doesn't necessarily care. But it's something an adult needs to do, and the skills go way beyond breakfast." The exercise is one of planning, navigation, memory, and execution. Eventually, he'll travel to the grocery store using public transportation, remember why he's there and what he needs, and then gather and buy it. Simple tasks requiring a thousand minute computations.

Sandlin scans the list -- ramen noodles, peanut butter, Honey Nut Cheerios. She asks questions, forcing Welsh to concentrate, probing his memory. She taps the list with her pen and says, "What do you think you'll want to drink besides Coke and milk?"

Welsh's injury was relatively mild. The MRI revealed "diffuse axonal injury" -- shearing and twisting of axons -- mainly in the right lobe, and some in the left. After the injury, portions of his brain had dif?culty communicating, signals were interrupted, the network damaged. He has had problems with memory, multitasking. He loses focus, and sometimes his temper flares erratically. He curses more, and his sense of smell and touch have weakened. Welsh also suffers survivor's guilt, especially about Crombie. "I let him down," Welsh says. "I didn't even know him long enough to learn anything about his personal life."

While talking, Welsh will pause, as if the current of thoughts had suddenly hit a dam. He searches for words. "Sometimes I have to stop and think. It's pretty embarrassing. I'm aware that it's not back yet. I can feel myself think slower, step by step, instead of just reacting. I hate it." Welsh spends hours each day working with therapists, developing ways to compensate for mental abilities that may take months to return, if they ever return at all. Still, through all of this, he has retained the major connections and patterns that form his personality.

Two months after his injury, Welsh is nearly ready to move into the clinic's independent apartment, where he will no longer be under 24-hour supervision. He has just been given a job at the nearby Judge Advocate General's Legal Center and School, which trains military lawyers. He'll wear his camouflage uniform, his sergeant's stripes. The job will help him practice social interaction and problem solving -- some of the same skills the grocery shopping exercise focused on.

Welsh can't wait. He considers his injury a temporary setback. Returning to the infantry is all he wants, even if it means another tour in Iraq. "I feel like I've got a lot of leading left to do, a lot of teaching," he says. "Those guys in Iraq need experience, and I can give them that."

It's not clear yet whether the Army will allow Welsh to return to his old job. But his therapists have dedicated themselves to helping him progress as far as possible. One therapist describes Welsh as essentially normal, meaning he has regained, or developed compensations for, much of what he lost that night in Ramadi.

From the battlefield to the home front, Welsh has received the best medical care available anywhere, but his case reveals the limitations even of the massive military system. Early assessments missed his brain injury. And there are others like him. Many experts -- including Dr. George Zitnay, who founded Virginia NeuroCare as well as Walter Reed's Defense and Veterans Brain Injury Center -- have pressed the Department of Defense to screen returning veterans for brain injuries. The department has only recently begun limited screening.

Welsh's mother, Lynne, visits him for several days in Charlottesville to check on his recovery. One evening, over burgers and iced tea at a restaurant in a local strip mall, Lynne reminisces with Jason about his years as a headstrong kid with a mischievous streak and a disdain for authority. Her voice is raspy and midwestern. The pair joke and laugh, remembering. For Lynne Welsh, the fear is fading. She knows she's fortunate, watching the old Jason reemerge. She knows that many soldiers never do.