In itself, walking may not be one of the most complex functions we can perform with our bodies. Nonetheless, watching someone once paralyzed get up and walk again is a powerful sight to see. So it must have been one incredible moment for a team of researchers who were able to make partially paralyzed monkeys walk after implanting them with a pair of devices that bypass broken nerves in the spine. The finding raises exciting new prospects for treatment in humans with spinal cord injuries.
The research was recently published in Nature and works by placing one implant in the brain near the motor cortex and another in the spinal cord controlling muscle movement in the leg.
“The primate was able to walk immediately once the brain-spine interface was activated. No physiotherapy or training was necessary,” said neuroscientist Erwan Bezard of Bordeaux University who oversaw the primate experiments.
The technology works by placing a dime-sized electrode on a part of the monkey’s brain that controls motor signals. While in humans, the leg-controlling part of this region of the brain is located further inside, it’s closer to the surface in monkeys and is easier to access. Once the electrode picks up signals for leg motion, it wirelessly sends the information to a computer to interpret. The computer then sends the commands to the second implant, an electric-pulse generator located below the damaged part of the spinal cord. The second implant causes the leg muscles to extend and flex according to the signals of the brain. It makes for an imperfect gait but the technology does get the rudimentary movements out with small enough delay for functional walking.
The team was led by Grégoire Courtine, a neuroscientist at the École polytechnique fédérale de Lausanne (EPFL) in Switzerland, and their research restored movement in the legs of two paralyzed rhesus macaques within weeks of injury. Both monkeys gained full mobility within three months.
Already following the experiment’s success, Courtine is preparing to conduct human trials in Switzerland using a pared-down version of the technology. Two people have so far been implanted with the electric-pulse generator in their spinal cord. For now, they won’t receive the brain implant to control movements with brain signals and Courtine states it could take years to get all the components of this technology tested on humans.
But the potential application is still clear. The implants won’t fully restore locomotion but should help strengthen neural circuits to speed up recovery after injury. While patients work on regaining balance and control, the implants could temporarily reconnect the link between brain and spinal cord to generate the muscle movement needed to walk.
It should also be noted that for the sake of the experiment, Courtine and his team paralyzed monkeys in Beijing – where attitudes about animal testing are more welcoming than in Europe or the U.S. The researchers took care to adhere to animal research standards by transecting the spinal cord in a way that made paralysis temporary. But he still moved part of the experiment to China because of the potential controversy surrounding experimentation.
It’s a stark reminder of how medical research has the freedom to move around in a globalized world. But it does raise the question of what kinds of animal research society should accept. If some countries collectively say no to such research, is it acceptable to then reap the rewards of innovations derived in countries that do allow it? There are no easy answers to this problem. And in the meantime, as Europe and the U.S. continue to crack down further on animal testing, China is poising itself to become a competitive destination for medical research.