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Weird treadmill may tap nerve networks for better walking

WASHINGTON – A weird treadmill is pushing people at Kennedy Krieger Institute into sloppy versions of Michael Jackson’s moonwalk, in hopes of training stroke survivors and others with brain injuries to walk normally again.

The custom-built treadmill hides a split belt – one side can move one foot backward while the other moves forward, and at different speeds.

It can be a wild ride: Your brain must automatically adjust how you walk so you won’t fall down.

Scientists at Kennedy Krieger are tapping into that unconscious adjustment, using a brief workout to jolt patients who usually limp and lurch back into a normal stride, one they retain for a few minutes after the treadmill stops.

Watch a young patient’s progress. (VIDEO)

The discovery: Separate nerve networks control how each leg moves, networks that can be retrained to change someone’s innate walking patterns, at least temporarily.

Now the challenge is to make the better walking permanent. This fall, Kennedy Krieger’s Dr. Amy Bastian will begin a government-funded study putting at least 40 stroke survivors through longer sessions with the wacky treadmill, to see if practice helps the improvement stick.

Because Kennedy Krieger is a pediatric research institute, she hopes eventually to begin a similar study with children recovering from major brain surgery.

The findings offer a glimpse into the newest frontier in rehabilitation research: How to spur brain and spinal cord circuitry to rewire itself for normal leg control after a stroke or other brain injury.

"The amazing thing about walking control (is) when you try to consciously override things, it doesn’t work so well," says Bastian, who has personally tested the treadmill.

"The belts start moving and if you think about it, you start to screw it up. If you just let your system take over, it’s these lower, less conscious control networks that can do this, no sweat," she explains. "Those are the ones we want to train."

A healthy brain continually adapts and reorganizes itself, a condition called plasticity. It’s easiest for younger brains, but it is possible to spur this process even in older people. For example, tying down a stroke victim’s good arm while repeatedly exercising the weak one strengthens arm circuitry in the stroke-damaged brain region while improving movement.

Far less research has been done on ways to improve rehab for the legs, however.

The split-belt treadmill is "a fascinating concept," says Dr. Milton Thomas of the Baylor Institute for Rehabilitation, who was amazed that Bastian’s experiments didn’t have people falling down. The research "showed both legs are taught to function almost independent of each other – or can be."

First, Bastian tested the funky walking on 40 healthy people. Sometimes, the treadmill moved their legs in opposite directions. Sometimes it moved one leg up to four times faster than the other.

With a 15-minute session, she essentially retrained them to walk with a lurch. No matter how hard they tried to walk normally when the session ended, they couldn’t for 10 minutes or so – until automatic nerve systems recalibrated themselves again.

Tracking that adjustment, Bastian reported in the journal Nature Neuroscience last month that there are separate neural networks to control forward walking and backward walking, and each leg, too. That means researchers might target just the bad leg.

What about people with brain injuries? Thirteen stroke survivors who had limped for months saw that same brief improvement from the treadmill test, Bastian and University of Delaware physical therapist Darcy Reisman reported in the journal Brain.

That suggests the right circuitry for good walking is lying dormant in these patients, if doctors can learn to tap it.

Then Bastian tried the technique with a few children relearning to walk after surgery removed half of the brain to stop seizures. Video shows Beth Nielsen, then 4.5, pointing her right foot outward and dragging it. After a treadmill session, she strides correctly for a few minutes.

"One of the highlights of her day was to get to do that," says her mother, Sharon Nielsen, of Woodbury, Minn.

Beth went on to regular physical therapy, and six months later Nielsen says she walks fairly well unless she’s tired.

A split-belt treadmill isn’t the only approach under study. The Baylor Institute for Rehabilitation in Dallas is having success training brand-new stroke victims to walk normally by giving them specially supervised sessions on a regular treadmill as soon as they can stand but before they’ve tried walking on their own.

"We’re extraordinarily excited about this," Thomas says.

But this is key: Wait until six months after the stroke and the Baylor method is too late. Patients who try walking on their own immediately compensate for the weak leg with a limping gait that the body soon adopts as its new normal, he explains.

So Thomas was impressed that the Baltimore team is tackling long-term limpers.

"The fact that these guys were able to disrupt the (ingrained) pattern is, I think, groundbreaking," he said. "It’s going to be really interesting to see what comes of this."