Two monkeys, each with a paralysed leg, were able to walk again days after spinal injury – all thanks to a wireless, implantable brain chip system, a study reported in Nature has shown.
Known as the “brain-spine interface”, the technology lets brain signals skip a damaged section of the spinal cord by being beamed to a recording device, then a computer, and finally to a pulse generator implanted in the lower spine to activate the legs.
It was developed in an international collaboration of researchers led by Grégoire Courtine from the Swiss Federal Institute of Technology in Lausanne who has had previous success restoring mobility to paralysed rats. But it's the first time neurotechnology has brought back movement in paralysed primates.
Walking seems like one of the most natural movements in the world, but it starts with a highly coordinated set of signals from the brain down the spinal cord to the lumbar region, which is responsible for activating legs. If the spinal cord about the lumbar is damaged, it can interrupt those signals.
So to see if these signals could bypass a spinal cord injury above the lumbar area, Courtine and colleagues gave rhesus monkeys a lesion near the middle of their spine. This meant one leg was paralysed.
Close-up of the pulse generator
A pill-sized implant, made of almost 100 tiny electrodes, was inserted into the monkeys’ motor cortex – the small part of the brain that sends signals telling our muscles to move. The implant transmitted brain signals to a recording device, which relayed the information wirelessly and in real time to a computer. Algorithms decoded the signals and extracted the message to move – called a motor state – from the brain activity.
The motor states were then translated into spine stimulation protocols, which, in turn, triggered a pulse generator implanted in the spine's lumbar region to get leg muscles moving. Study co-author Marco Capogrosso, also from the Swiss Federal Institute of Technology, says at first he wasn't optimistic about it working but “looked on in disbelief” when the first primate tested began moving its “paralysed” leg.
“All the science that we built to get there, all the problem solving and the technological solutions that we had to put together, all the systems that we integrated were just working smoothly all together at the same time,” he says.
Similar work from the US this year resulted in a quadriplegic man able to use his hand again. But Capogrosso says leg movements which need to sustain weight and propel the body forwards need different strategies.
“Locomotion may look simpler to achieve than grasping because it is patterned and repetitive,” he says. "However, in reality, it is not."
Within a week after the device was switched on, one of the monkeys regained some mobility without training, walking on the treadmill at a comfortable pace. The other monkey had a more damaging injury and took two weeks to reach the same point. The brain-spine interface uses components that have been approved for research in humans. But there are still some challenges and limitations in the system to overcome, and it will take several years for the technology to be fully available to humans.
For instance, the monkeys could only walk as far as the wireless connection would allow. In the researchers' set-up, this was less than five metres. Capogrosso says the researchers aim to embed the computer functions into another chip for a fully implantable system – or to a smaller device such as a smartphone.
Watch footage of the monkeys walking in the video below.