The French neuroscientist was watching a macaque monkey as it hunched aggressively at one end of a treadmill. His team had used a blade to slice halfway through the animal’s spinal cord, paralyzing its right leg. Now Courtine wanted to prove he could get the monkey walking again. To do it, he and colleagues had installed a recording device beneath its skull, touching its motor cortex, and sutured a pad of flexible electrodes around the animal’s spinal cord, below the injury. A wireless connection joined the two electronic devices.
The result: a system that read the monkey’s intention to move and then transmitted it immediately in the form of bursts of electrical stimulation to its spine. Soon enough, the monkey’s right leg began to move. Extend and flex. Extend and flex. It hobbled forward. “The monkey was thinking, and then boom, it was walking,” recalls an exultant Courtine, a professor with Switzerland’s École Polytechnique Fédérale de Lausanne.
In recent years, lab animals and a few people have controlled computer cursors or robotic arms with their thoughts, thanks to a brain implant wired to machines. Now researchers are taking a significant next step toward reversing paralysis once and for all. They are wirelessly connecting the brain-reading technology directly to electrical stimulators on the body, creating what Courtine calls a “neural bypass” so that people’s thoughts can again move their limbs.