“It tells us that the information from the brain is getting to the right place in the spinal cord, so that the person can control, with fairly impressive accuracy, the nature of the movement,” said Edgerton. “We don’t have to necessarily rely on regrowth of nerves in order to regain function. The fact that we’ve observed this in all four patients suggests that this is actually a common phenomenon in those with complete paralysis.”

The stimulator was originally developed by Medtronic to treat chronic pain. It’s a pacemaker-sized device implanted under the skin of the abdomen, connecting to electrodes placed near the spinal cord. When turned on, it delivers a low pulse of electricity.