Bypassing paralyzed nerves

Implanted electrode helps paralyzed monkey clench its forearm muscles

It’s a case of mind over muscle, by way of machine. By electronically connecting a monkey’s forearm muscles to its brain, researchers gave a temporarily paralyzed monkey the ability to clench those muscles.

An electrode implanted in the monkey’s brain picked up the electrical signal from a single neuron, and the monkey learned to control the activity of that neuron to regain control of its wrist — even if the neuron was in a sensory rather than a muscle-controlling region of the brain.

It’s a powerful demonstration of the brain’s flexibility, and the first time that scientists have electronically linked a single neuron to an animal’s own muscles, researchers report in the Oct. 16 Nature.

Such an artificial connection could replace the electrical signals that nerves normally carry to muscles, but that, in people with paralysis, are blocked, the researchers suggest.

“We were interested in developing a potential treatment for paralysis, whether it’s from spinal cord injury or other injury,” says study coauthor Chet Moritz of the Washington National Primate Research Center in Seattle. The current experiment is only meant to show that such an electronic connection is possible, Moritz adds. More work is needed before the technology could be ready for use in people. “We are several years away if not several decades away.”

But some scientists are skeptical of whether the new technique will ever be well suited for restoring motion in paralysis patients. In the experiments, the monkey only had to learn to control two muscles, which pushed and pulled its wrist in a motion like revving a motorcycle. Its arm was otherwise braced and immobilized.

In more natural situations, even simple motions require the coordinated control of a dozen or more muscles. Reach forward to press a button, and muscles in your torso, back, shoulder, upper arm, forearm and hand will all contract in concert.

With the approach from Moritz’s team, a patient would have to learn to control each muscle separately, and then consciously coordinate perhaps 20 or so muscles to achieve even one simple task. “That to me would be extremely complex and probably very difficult to train a subject to do,” comments Andrew Schwartz, a neurobiologist at the University of Pittsburgh in Pennsylvania.

Schwartz has previously connected a monkey’s brain to a robotic arm using a different technique that gave the monkey control over its arm that was more complex.

Schwartz’s team first watched the monkey’s brain activity while it used its own arm in a natural way. Decoding this neural activity allowed the researchers to later wire the monkey’s brain to a robotic arm that would adapt to the monkey, instead of making the monkey adapt to it. That way, the monkey could simply “will” the movement to happen without having to concentrate on contracting individual muscles.

All this decoding of brain impulses takes the computing horsepower of a modern desktop computer, though. The advantage of Moritz’s approach is that the signal from a single neuron can be interpreted by a much less powerful computer chip, perhaps one small and low-powered enough to implant into the animal’s — or a patient’s — body.

Moritz also suggests that his team’s approach could eventually control several muscles at once by electrically stimulating nerves in the spinal cord, rather than stimulating the muscles directly. Eventually the researchers hope to develop wireless electrodes that wouldn’t involve wires sticking out of the skull, Moritz says.

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