Bypassing the Injury May Put Brain Back in Charge of Paralyzed Muscles, Study Shows
WebMD Health News
Reviewed By Louise Chang, MD
Oct. 15, 2008 -- Scientists at the University of Washington in Seattle report success in their first attempts to harness the brain to treat paralysis in people with spinal cord injuries.
Their technique isn't ready for patients yet, but researcher Chet Moritz, PhD, says it may one day be used to help paralyzed people walk.
"We haven't studied that directly, so it's all speculation on my part, but certainly it's possible in the next 10-20 years," Moritz said at a news conference.
The basic idea is to bypass the spinal cord injury and create a direct route from the brain to the muscles. It's a concept that hinges on the brain's ability to adapt, with brain cells stepping up to handle tasks that they're not used to doing.
Here's a look at the findings, published in today's advance online edition of Nature.
Moritz and colleagues tested their treatment on monkeys. First, the monkeys learned to play a simple video game which involved flexing and extending the wrist muscles. A little applesauce was all the reward the monkeys needed to master the game.
Then, the researchers temporarily paralyzed the monkeys' wrist muscles with a nerve-blocking drug. The scientists also implanted electrodes in the monkeys' brains to record the activity of certain brain cells.
Those electrodes were hooked up to wires running to a computer and then into the monkeys' wrist muscles -- basically, a direct connection wiring brain cells to the wrist muscles, bypassing the temporary nerve blockage.
With that gear in place and their wrist nerves blocked, the monkeys kept trying to play the video game, still motivated by applesauce. And they managed to do it.
"We found that, remarkably, nearly every neuron that we tested in the brain could be used to control this type of stimulation. We also found that monkeys could learn very rapidly to control newly isolated neurons in order to stimulate their muscles," even with brain cells that don't usually govern the movement of wrist muscles, Moritz says.
The study is "very exciting," says Edelle Field-Fote, who directs the Neuromotor Rehabilitation Research Laboratory at the University of Miami Miller School of Medicine's Miami Project to Cure Paralysis.
Other studies have used a similar approach to control robotic devices, but not the muscles themselves, notes Field-Fote. Still, she sees challenges ahead.
One of those challenges is working the muscles just enough to get the task done -- for instance, picking up a can without crushing it. "Just controlling the muscles isn't enough to give us fine control of muscles to be able to manipulate objects in space," says Field-Fote. She says walking may actually be easier in that regard, because it relies on large muscles more than small muscles moving in several directions.
Another hurdle is that switching muscles on externally activates the biggest muscles first, and those muscles tire out faster than smaller muscles. That's one of the reasons why electrical stimulation of muscles hasn't been widely used in people with spinal cord injury, says Field-Fote.
One way to overcome that might be to stimulate the spinal cord below the patient's spinal cord injury, says Field-Fote. That way, the spinal cord transmits the signal to the muscles, and because the muscles aren't being stimulated externally, they turn on in the right order, from smallest to largest.
That's one of the tasks Moritz and colleagues have already set for themselves. "That's good," says Field-Fote. "It sounds like they're barking up the right tree."
Other challenges include developing a system that can safely be implanted under the skin, improving electrodes' ability to record brain cell activity for longer periods of time, and creating a system where enough brain cells are harnessed so that if one bows out, the patient can still move. And developing a wireless system could cut infection risk, notes University of Washington professor Eberhard Fetz, PhD, who worked on the study.
Moritz predicts that researchers will first target paralysis that only affects one area of the body -- say, teaching the brain to use the hand muscles to pick up a coffee cup or toothbrush.
"If we want to speculate wildly about the future and we want to restore movement to all parts of the body in a quadriplegic patient, where both arms and legs are paralyzed, we're going to need a larger set of neurons that can restore all those movements," Moritz says.
For now, the monkey experiment shows that the technique can work, but "certainly we're several years, if not several decades, away from this being ready for a clinical application," Moritz says.
SOURCES: Moritz, C. Nature, Oct. 15, 2008; advance online edition. Chet Moritz, PhD, department of physiology and biophysics and Washington National Primate Research Center, University of Washington. Eberhard Fetz, PhD, professor, department of physiology and biophysics and Washington National Primate Research Center, University of Washington. Edelle Field-Fote, PhD, PT, director, Neuromotor Rehabilitation Research Laboratory, Miami Project to Cure Paralysis, University of Miami Miller School of Medicine.
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