Paralyzed Monkeys Walk With Help Of Neural Interface

System uses still functional parts of the spine to restore motion to the legs

Nov 10, 2016 at 1:56 PM ET

Even a devastating spinal injury doesn’t leave the entire spinal cord useless. Much of the spine is still perfectly functional but cut off from communicating with the brain. Now an international team of researchers have shown it’s possible to restore that connection between brain and spine, giving temporarily paralyzed monkeys the ability to walk.

There’s been a lot of research recently into different ways to restore motor function after spinal injury. Some work has looked at computer interfaces to control limbs or using the brain to control robotic limbs, while others have focused on having the brain stimulate the muscles directly. What sets this research apart is how much of the body’s existing circuitry it uses.

The spinal cord is unfortunately called the spinal cord, but it really is a spinal brain,” Brown University researcher David Borton told Vocativ. “There are computation centers all along the spinal cord just like in your brain, all sorts of networks that are trained over your lifetime. We’re not bypassing those. We’re leveraging those.”

In their model, a wireless interface took in motor signals recorded by a device implanted into the brains of rhesus monkeys, who had been temporarily paralyzed for the purpose of the experiment. The neural interface then decoded and transmitted those signals to the spinal cord, which was able to signal the monkeys’ legs to move like normal.

“We’re stimulating the spinal cord, the nervous system itself,” said Borton. “We’re using brain signals to go back into the nervous system and bypass the injured site.”

In undamaged nervous systems, the motor cortex in the brain sends signals to the lower spinal cord, which activates the neurons that control walking and other movement by the legs. When an injury occurs to the upper spine, that doesn’t actually affect the lower spine’s ability to control the rest of the body. It’s just that it can’t send or receive signals anymore. This system changed that for the rhesus monkeys, and it could eventually do the same for injured humans.

“One way to put it is helping the brain help itself, helping the nervous system help itself,” said Borton.

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There are limitations to this system, chief among them the fact that this is still one-way communication: The brain can use this interface to send signals to the spinal cord, but it can’t receive information back. That means the brain can’t feel the leg as it moves. It also can’t be taken as a given that what works in rhesus monkeys will work just as well in humans, although Borton is optimistic as the researchers begin the move toward clinical trials. In particular, he sees the successful coordination of the different parts of the interface in the brain and spine as particularly promising for future application in humans.

“I think it bodes well that really we’re testing many technologies working in concert to produce a particular outcome, and that part spans many different potential diseases or injuries,” said Borton. 

No two spinal injuries are alike, with anything from car accidents to knife wounds causing very different damage in the spine. Borton said the system should prove flexible enough to help restore movement in the legs, regardless of the reason for the injury.