The stroke paralyzed her arm. This implant allowed her to use it again.

“It’s very interesting,” says Jason Carmel, a Columbia University motor neuroscientist who was not involved in the study. “This opens up potential treatment options that we never had before for people with chronic stroke.”

Stroke is the most common cause of disability in adults. World, every fourth person over 25 will suffer once in a lifetime, and three quarters of them will have prolonged motor deficits in the arm and hand.

A stroke happens when the blood supply to the brain is blocked or when a blood vessel bursts. Depending on the severity of the brain damage and where it occurs, a stroke can cause certain impairments, such as paralysis, weakness, or problems with speech, thinking, or memory.

People with paralysis after a stroke cannot voluntarily move a particular muscle or group of muscles. When the part of the brain that controls movement is damaged, it disrupts the communication between the brain and muscles. Patients who recover often do so within the first few months after a stroke. After six months there is little chance of further improvement. This is the chronic stage of a stroke, when the effects are usually irreversible.

Both Rendulik and the other patient were in this phase, and the researchers wanted to see if they could use a weak electrical current delivered to specific locations in the spinal cord to restore muscle function in the arms and hands. The spinal cord is a long tube of nerves in the back that carries messages from the brain to the rest of the body.

Spinal cord stimulation is already being used to treat pain, and in 2018 separate research commands published a series of papers showing that it allowed several patients paralyzed due to spinal cord injuries to stand and walk independently with assistive devices for the first time in years. But stimulation of the spinal cord for the recovery of the upper limbs is practically not studied.

In the latest study, surgeons implanted a pair of thin, spaghetti-like metal electrodes along the top of the spinal cord in the neck to target populations of nerves that control muscles in the arms and hands. The electrode cables were laid outside the skin and connected to the stimulation system in the laboratory.

On the day the researchers turned on the electrical stimulation, Rendulik was able to fully open and close her left arm, something she hadn’t been able to do before. “We were all in tears,” she says. “I opened my hands in a way that I hadn’t done in almost ten years.”

Over the course of four weeks, Rendulik and another patient ran a series of laboratory tests. (The second patient, a 47-year-old woman with a more severe deficiency, had a stroke three years earlier.) They performed tasks such as moving blocks, picking up marbles, grabbing a can of soup, and opening a lock. While Rendulic showed greater improvement than the other patient, stimulation increased strength, range of motion, and function of the arm and hand in both women. Rendulik says that when the device was turned on, she felt a slight vibration in her hand, but it didn’t hurt.