The war in Iraq is not over, but one legacy is already here in this city and others across America: an epidemic of brain-damaged soldiers.

Thousands of troops have been diagnosed with traumatic brain injury, or TBI. These blast-caused head injuries are so different from the ones doctors are used to seeing from falls and car crashes that treating them is as much faith as it is science.

"I've been in the field for 20-plus years dealing with TBI. I have a very experienced staff. And they're saying to me, 'We're seeing things we've never seen before,'" said Sandy Schneider, director of Vanderbilt University's brain injury rehabilitation program.

Doctors also are realizing that symptoms overlap with post-traumatic stress disorder, and that both must be treated. Odd as it may seem, brain injury can protect against PTSD by blurring awareness of what happened.

But as memory improves, emotional problems can emerge: One of the first "graduates" of Vanderbilt's program committed suicide three weeks later.

"Of all the ones here, he would not have been the one we would have thought," Schneider said. "They called him the Michelangelo of Fort Campbell" — a guy who planned to go to art school.

As more troops return from the war, brain injuries are a growing burden — for them, for the few programs to treat them, and for taxpayers who pay for their care and disability if they cannot hold jobs.

Most TBIs are mild, and most of these patients recover within a year. But one-fifth of the troops with these mild injuries will have prolonged or lifelong symptoms and need continuing care, the military estimates. Nearly all of the moderate and severe ones will, too.

Though the full number of those suffering from TBI is still unknown, the problem is straining the U.S. Department of Veterans Affairs. Until now, "they were dealing with a cohort of aging veterans with diabetes, heart disease, lung disease," said Dr. Jeffrey Drazen, editor-in-chief of the New England Journal of Medicine and a VA adviser.

Now, these young, brain-injured troops need highly specialized care, and how much it will help long-term is unknown, he said.

People with TBI have frequent headaches, dizziness, and trouble concentrating and sleeping. They may be depressed, irritable and confused, and easily provoked or distracted. Speech or vision also can be impaired.

Some sufferers have been misdiagnosed with personality disorders. Others have lost jobs because of unrecognized and untreated symptoms.

"It's the so-called invisible injury. It's where a troop takes 10 times the normal time to pack his rucksack ... a complicated injury to the most complicated part of the body," said Dr. Alisa Gean, a neurosurgeon at the University of California, San Francisco.

Diagnosing it is imprecise — damage rarely shows up on CAT scans or other tests.

Treating it is even more difficult. Lacking a cure, doctors focus on symptoms — headaches, anxiety, vision problems, etc. But they lack good treatments for some of these, too, and are considering some experimental approaches being pushed by private companies with little proof they work.

Many troops get no care at all. Some are sent back to fight with their brain injuries undetected, especially if they had no obvious wounds.

Two Men, One Problem

What happened to Eric O'Brien and Bryan Malone shows the scope of this problem.

O'Brien, a 32-year-old Army staff sergeant from Iowa's Quad Cities, was teasing Malone, 22, a specialist from Haughton, La., in a Baghdad gym last summer.

"I told him and his workout partner: 'Put some more weight on it,'" prompting the men to get up. Seconds later, a rocket hit where they had sat. They survived, but a pressure wave from the blast coursed through their brains.

"I patted myself down head to toe, making sure I wasn't missing a limb," and felt odd, like "I must be missing a chunk of my head,'" O'Brien said. He remembers little else except walking through debris to pick up his iPod and sunglasses.

As for Malone, an air conditioning vent had fallen on his head and he had shrapnel wounds. He had multiple surgeries, spent several months in Walter Reed Army Medical Center and now has titanium mesh reinforcing his skull.

O'Brien, however, had shrapnel removed from his scalp and then was sent back to his unit — "no antibiotics, no pain medication or anything. They just sent me on my way."

When he later complained of pain, doctors gave him Motrin. When he discovered a trickle of blood from his hip, they said he would be fine. Six weeks later, when he could barely walk, tests revealed shrapnel in his hip. By then, he was having headaches and trouble sleeping.

O'Brien had been through multiple previous explosions — troops average one a month, a study found — and each raises the risk that the next one will do harm. Soldiers and Marines are proud and reluctant to go "off mission" just because "they get their bell rung," said Dr. Michael Kilpatrick, a top Defense Department physician.

"Most of the treatment is explaining the situation and giving the tincture of time — giving it time to heal," he said. If no big symptoms appear in eight to 12 hours, "they're probably ready to go back."

Officers also face pressure to return troops to duty, said Jordan Grafman, a neuroscientist who studies TBI at the National Institutes of Health.

"People don't want to lose these guys from their command — they can't replace them fast enough," he said.

During a surprise visit to Iraq with President Bush on Labor Day, Gen. Peter Pace, chairman of the Joint Chiefs of Staff, said the military was "much smarter about this now," and urged troops to watch for signs of TBI and post-traumatic stress.

"They are every bit as much battle injuries as is a bullet or shrapnel. It is OK, it is OK to seek help for those kinds of war wounds, and I ask you all to help your buddies understand what you see in them," he said.

But that was long after O'Brien was hurt. His TBI was not diagnosed for months, until his hip injury landed him back at Fort Campbell in Kentucky. By then, the Army needed help treating TBI and was contracting with private rehab centers like Schneider's at Vanderbilt.

Malone and O'Brien had become friends, helping each other cope with wounds.

"They were sent to us together," Schneider said.