Capogrosso M, Milekovic T, Borton D, Wagner F, Moraud EM, Mignardot JB, Buse N, Gandar J, Barraud Q, Xing D, Rey E, Duis S, Jianzhong Y, Ko WK, Li Q, Detemple, P, Denison T, Micera S, Bezard E, Bloch J, Courtine G. A brain-spine interface alleviating gait deficits after spinal cord injury in primates. Nature. 2016 Nov 9;539(7628):284-288.
Spinal cord injury disrupts the communication between the brain and the spinal circuits that orchestrate movement. To bypass the lesion, brain-computer interfaces have directly linked cortical activity to electrical stimulation of muscles, and have thus restored grasping abilities after hand paralysis. Theoretically, this strategy could also restore control over leg muscle activity for walking. However, replicating the complex sequence of individual muscle activation patterns underlying natural and adaptive locomotor movements poses formidable conceptual and technological challenges. Recently, it was shown in rats that epidural electrical stimulation of the lumbar spinal cord can reproduce the natural activation of synergistic muscle groups producing locomotion. Here we interface leg motor cortex activity with epidural electrical stimulation protocols to establish a brain-spine interface that alleviated gait deficits after a spinal cord injury in non-human primates. Rhesus monkeys (Macaca mulatta) were implanted with an intracortical microelectrode array in the leg area of the motor cortex and with a spinal cord stimulation system composed of a spatially selective epidural implant and a pulse generator with real-time triggering capabilities. We designed and implemented wireless control systems that linked online neural decoding of extension and flexion motor states with stimulation protocols promoting these movements. These systems allowed the monkeys to behave freely without any restrictions or constraining tethered electronics. After validation of the brain-spine interface in intact (uninjured) monkeys, we performed a unilateral corticospinal tract lesion at the thoracic level. As early as six days post-injury and without prior training of the monkeys, the brain-spine interface restored weight-bearing locomotion of the paralysed leg on a treadmill and overground. The implantable components integrated in the brain-spine interface have all been approved for investigational applications in similar human research, suggesting a practical translational pathway for proof-of-concept studies in people with spinal cord injury.
When a person becomes paralyzed, most – but not all – of the neurons that help signal muscles to move are broken. This keeps the brain from being able to send signals to certain muscle groups telling them to move. But if the body had a way of strengthening the few intact neurons, they might be able to do the heavy lifting themselves and restore the ability to move.
In the new study, researchers implanted tiny wireless devices into the brains of two monkeys that had been purposefully paralyzed -- each lost the use of a hind leg. The device recorded electrical signals from the brain’s motor cortex, which controls movement, and sent them to a computer. The computer then translated those signals into a language that electrodes -- connected to a group of neurons in the spinal cord -- could understand. Their work was published this week in the journal Nature…
As seen in the video [at link], the monkeys were able to move their paralyzed legs in conjunction with the other four as they walked. And unlike similar technologies that require a person (or monkey) to be somehow wired to a computer, this new technology is completely wireless. The monkeys wear a backpack which interprets and sends off the brain signals.
This success is just one of several achievements made in the last few years as scientists continue to better understand how electrical signals in the brain enable movement. But it's unique, and not just because it ditches the usual cords: In an accompanying commentary on the study, Newcastle University neuroscientist Andrew Jackson points out that the new device is a "closed-loop stimulation", which interprets brain signals in real time. The devices that are currently in use in humans with paralysis are open-looped, meaning they require repeated stimulation to excite or wake up the neurons that may have survived the patient's injury. That strengthens those neurons, but the closed-loop system strengthens the entire network connection of neurons between the brain and spinal cord.
But while this is a successful proof-of-concept experiment, work on creating a brain-computer interface suitable for humans is far from complete. The system used here is successful in allowing for broader muscle movements, like moving a leg to walk, but it would be less successful at allowing for more fine tuned movements like a small change in direction or enabling a person to balance. As research forges ahead, scientists will need both a better