Paralysed monkeys walk again with brain implant

Paralysed people could walk again instantly after scientists developed a brain implant which turns thought into electrical signals in the spine so that lost feeling can be restored after injury.

Currently people who break their backs or suffer a spinal trauma are unable to stand or move even though their legs still work, because the signal which connects their brains to their muscles is disconnected.

But an international team of scientists have shown it is possible to bypass the injury and reconnect the brain signals to electrodes at an undamaged part of the spine.

Some animals have walking reflexes governed by nerves in their spine – it’s why a chicken continues to run after its head has been cut off. Now these reflexes have let paralysed monkeys regain use of their legs after a week or two of practice. Previous methods have taken months.

We have no reliable means to reconnect severed nerves in people with injured spinal cords. One way to overcome paralysis might be to detect a person’s desire to move and use this to stimulate nerves or muscles.

Last year, a paralysed man walked thanks to a cap of electrodes that read his brainwaves, and implants that stimulated his leg muscles. But directly stimulating muscles in this way can make movements jerky and uncoordinated. “Walking is a very complex behaviour: you need to coordinate the activity of hundreds of muscles and maintain balance,” says Grégoire Courtine at the Swiss Federal Institute of Technology in Lausanne.

This coordination is usually carried out by circuits in the spine, which control walking once it has been initiated by the brain – as happens in headless chickens. Courtine’s team has found a way to exploit this using spine implants in monkeys.

The spinal cord was severed on one side above the implant, and a second implant put into the part of the brain that controls the affected leg. This implant detected when the monkey wanted to move and sent signals to the device in the spine. Within six days, the first monkey was crawling using both legs. A second animal did so in two weeks (Nature, DOI: 10.1038/nature20118).

“Walking is very complex: you need to coordinate hundreds of muscles and maintain balance“
This is the first time implants have reversed paralysis in monkeys. “We are turning a corner,” says Chad Bouton at the Feinstein Institute for Medical Research in New York, who was not involved with the study.

But Courtine says it is unclear if reflexes could let paralysed people walk upright as easily. And the method might not work for long. Bouton’s team has used this kind of implant to return arm movements to a paralysed man, while another team used implants to give a person control of a robotic arm. But such implants tend to stop reading the signals so well after a few years. Both groups are now working on making them last longer.