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Among the devastating consequences of her brain injury from a gunshot wound 10 months ago, Arizona Congresswoman Gabrielle Giffords lost the ability to talk. But with help from music-based therapy, according to an ABC News segment that aired this week, Giffords has rediscovered her voice and, it seems, her spirit.

The footage, which shows Giffords crying in frustration when she tries unsuccessfully to talk but looking joyful as she sings fluently, paints a dramatic picture of the power of music to help people overcome brain injuries.

Giffords' story also highlights both the potential and the limitations of a fairly new field of medicine.

Music brings so much pleasure to our everyday lives, and it would make sense if music also worked as a healing tool. But scientists are still awaiting solid data to prove what seems to work in case study after case study.

"It used to be thought that music was a superfluous thing, and no one understood why it developed from an evolutionary standpoint," said Michael De Georgia, director of the Center for Music and Medicine at Case Western Reserve University's University Hospitals Case Medical Center in Cleveland.

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"In the last 10 years, we've just started to understand how broad and diffuse the effect of music is on all parts of the brain," he added. "We are just starting to understand how powerful music can be. We don't know what the limits are."

As early as the post-World War II era, physical therapists noticed that Big Band music helped wounded veterans get up and learn to walk again, said Lee Anna Rasar, a musical therapist at the University of Wisconsin, Eau Claire.

Since then, researchers have documented a consistent pattern. When given a rhythm to walk to, people with Parkinson's disease, strokes and other forms of neurological damage are able to regain a symmetrical stride and a sense of balance. Each beat serves as an auditory cue that the brain uses to anticipate timing and regulate footfalls.

In the last decade, researchers have also begun to demonstrate ways that music-based therapies can help with speech recovery. In particular, a type of treatment called melodic intonation therapy has shown the greatest promise, Rasar said. Using a combination of rhythm, pitch, vision and hearing, the brain manages to sing words that it can't say.

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For Giffords, therapy started with songs like "Happy Birthday," said Maegan Morrow, the Congresswoman's music therapist at TIRR Memorial Hermann Rehabilitation Hospital in Houston. At first, Giffords would simply sing the word "you" after Morrow sang, "Happy Birthday to…"

Over time, Giffords learned to repeat ordinary phrases in a sing-songy voice. A song would gradually become a chant and finally a spoken phrase with the natural rhythm of speech.

Scientists are still working out the details of how this kind of therapy works. But one likely explanation is that music is represented in many areas of the brain, while just two brain regions process language. Music also tends to dig deeper, more well-worn pathways between neurons.

So, in patients like Giffords -- who suffered left-hemisphere brain damage that knocked out her Broca's area, a major language center -- often, at least some musical areas remain intact. Through music, then, patients can reach into their stored knowledge about words and use songs to create new connections for speech.

One way to understand how this might work is to imagine that someone has challenged you to to speak the lyrics of a song you haven't heard in 10 years. You probably can't do it. But if that song suddenly came on the radio, you'd likely be able to belt out every word.

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"One theory is that music as able to short-circuit the damaged area through repetition," Rasar said. "It creates a new pathway in and people can then use that pathway out."

The theory makes a lot of sense, but studies are only just starting to back it up, said Catherine Wan, a neurologist at Harvard Medical School.

In a recent study with six autistic children who could not talk at all, she and colleagues found that music-based therapy helped all of them better articulate words and phrases. The kids ranged from 5 to 9 years old. Some said their first words after just eight weeks of music-based therapy, Wan said, and that was after years of other kinds of treatments.

Her group is currently conducting the first randomized clinical trial, looking at the effects of melodic intonation therapy on speech recovery.

"As much as we would like to say that music is a powerful medium, I think it's important for people to test it rigorously to try to really tease out what are the components that are contributing to the effects," Wan said. "Is it because they are seeing a therapist five times a day or it's a new therapy so they're more motivated or is the therapy itself that is important?"

If nothing else, music can be a great morale-booster for patients with brain damage. Melodies are known to affect the hypothalamus and amygdala, which regulate emotions and moods through hormones like oxytocin and prolactin, both of which have consoling effects. And different kinds of tunes, De Georgia said, can raise or lower blood pressure as much as drugs can.

For Giffords, who spent months in the hospital and has faced a long haul toward recovery, music may have primed her to do the hard work she needed to do, Morrow said. The Congresswoman came in with a great love for all kinds of music, she added, from show tunes to pop rock, which probably helped her progress and she relearned how to talk and walk.

"Music is an automatic motivator," Morrow said. "It is the easiest way to get you in a good mood, to bring you out of the situation you're in and bring you to a new place."