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One Tuesday last month, Erin Smith, 25, was learning how to walk again.

She stood in a small, windowless room at the Miami Jewish Home and Hospital. Nine gauze pads stuck to her shin and calf, and spaghetti-like cables connected the pads to a computer called the "Neuroeducator." A monitor showed the electrical impulses sent by Smith's brain -- badly damaged in a motorcycle accident six years ago -- as she flexed her foot up and down. When she raised the foot, a blue line shot up like a stock chart on a good day.

As Smith watched the monitor, her brain was busy retraining itself to orchestrate the complex series of muscle movements required to walk. Standing in that windowless room, Smith was displaying one of the hottest buzzwords in neuroscience: plasticity.

Plasticity means an injured brain can reroute signals through existing pathways and grow new connections between cells. It means the mind -- in some cases, and given the right prompting -- can begin to heal itself.

Traumatic brain injury is the leading cause of death and disability for adults in their 20s and 30s. Every year, some 80,000 people suffer serious damage from injuries like Smith's, largely the result of car and motorcycle accidents.

Yet for a variety of reasons, traumatic brain injury has long been overlooked in the medical community and the public at large. The Centers for Disease Control and Prevention has called it a "silent epidemic."

"It's a messy problem -- it's not an easy injury to understand or to diagnose," says Dr. Ronald Hayes, director of the University of Florida's Center for Traumatic Brain Injury Studies. "Traumatic brain injury has been largely a neglected problem, medically and socially."

This neglect stemmed partly from the belief that little could be done for brain-injured patients because brain damage was irreparable. "That's what I was taught: Once you're an adult, any damage to the adult brain, you're toast," says Dr. Donald Stein, an Emory University neuroscientist. "That's absolutely false."

But experts say the new understanding of plasticity has yet to move from the laboratory to rehabilitation centers, which often rely on the old wisdom that brain-injured patients can improve only for the first year or two after their injury.

"The most amazing thing from our data is how many people are out there with brain injuries who actually have surviving and repairing brain tissue that is never discovered by traditional diagnosis," says Dr. Bernard Brucker, the University of Miami psychologist who runs the lab where Smith has been learning to walk again. "And, more importantly, they never have an opportunity to use it."

In the last decade, improved trauma care has increased the number of patients who survive serious head injuries. But improvements in rehabilitation have been slower in coming.

"You're much better off having a heart attack than a head injury," Hayes says. "We have the ability to diagnose a heart attack, and we have some reasonable therapies to manage cardiovascular disease. We have neither for traumatic brain injury."

"For years what we have taught people is if you had right-sided weakness, just learn to write with your left hand," says Dr. Ross Zafonte, director of rehabilitation at the University of Pittsburgh. "This was probably the wrong thing to be teaching, because the brain is plastic -- use facilitates recovery."

In a technique pioneered in stroke victims, patients struggle to use hands rendered nearly useless by brain damage. Many of the stroke patients show marked improvement after just a few weeks -- and scans show increased activity in brain regions surrounding areas affected by the stroke.

Researchers believe trying to use the weakened limbs creates new connections between existing cells. The training may also prompt the brain to recruit previously unused cells and pathways -- a process neuroscientists call "unmasking."

In Brucker's Miami lab, when Smith lifts her foot, the Neuroeducator's screen shows her how many of her brain's foot-moving neurons are firing, a process known as biofeedback. Watching the screen helps her brain rewire itself so she can walk again. Smith has been visiting Brucker's lab off and on for two years and working with a personal trainer between visits.

"We came in a wheelchair," her mother says of the first session. Now, with lumbering, stiff-legged steps, Smith walks in and out of the building on her own.

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