Between 255,000-600,000 Americans can't walk because of paraplegia, or leg paralysis usually linked to spinal damage. But Tomislav Milekovic, a researcher at the Swiss Federal Institute of Technology (EPFL) in Lausanne, Switzerland, and his colleagues have managed to get paralyzed monkeys to do just that according to a new study in Nature. Using a brain–spine interface, Milekovic successfully made two paralyzed rhesus monkeys walk. In the process they've leaped another hurdle in the journey to increase mobility in humans with spinal cord injuries.
"The spinal cord is an extension, in a way, of the brain," Molekovic told Motherboard by phone. It contains e conduits that transfer information from the brain to the muscle as well as its own neural networks, or circuits that control these movements.
When the spinal cord is injured the signal from the brain to these neural networks gets blocked. The brain-spine interface Molekovic and his colleagues designed overcomes this blockage, by using a series of sensors. They implant hardware in the monkey's brain that records the movement signals the brain is trying to send. That device communicates wirelessly to a computer, which decodes its intentions, and sends the movement signal to a series of devices implanted to a second set of implants located over the portion of the spinal column responsible for moving the leg.
Previous studies have shown some success in helping people with paralyzed hands. But this is the first study to show success in the more complex muscles of the leg thanks to two key advances. The first is the ability to communicate with the computer wirelessly – previous studies tended to use a wired communication device. It's easy to strap a monkey to a chair and see how it uses its arm. It's less easy to see how it would move its leg.
The second advancement is in the spinal implants themselves. Rather than implanting the devices in the spinal column, the implant was located beneath the skin, on the surface of the spinal cord but not inside its fluid which is less risky. And its potential isn't limited just to spinal cord injuries—they're currently investigating its application in Parkinson's patients who have lost the ability to walk.
As for the computer, "the only reason why the computer is there is because it allows some flexibility in how we change different algorithms that we use to control new activity and that we use to control the simulation," said Milekovic. A system that's robust and well developed enough to be used in humans would likely be a closed system—there wouldn't be a reason to extract the neural commands outside of the body or send simulations to the body.
And that system might be appearing sooner than we think.
"[it is] not unreasonable to speculate that we could see the first clinical demonstrations of interfaces between the brain and spinal cord by the end of the decade," wrote Andrew Jackson in a separate article in Nature. Jackson is a researcher at the Institute of Neuroscience at Newcastle University and did not take part in the study.
"This study is very promising. I hope it will make things move even more rapidly when you say rapidly it's never rapid enough for the people who have paraplegia," said Milekovic before going onto note, "our study was in large majority funded by the public research funds. And it was based on decades of studies which have also been publicly funded. Without continuing generous support of the public, it just wouldn't have been possible."