Four people who were paralyzed below the waist for more than two years were able to voluntarily wiggle their toes and flex their legs, thanks to a promising study that some are heralding as a breakthrough in spinal-cord-injury treatment.

The key to the achievement, say the study’s authors, was stimulation of the spinal cord using a commercially available electrical stimulator commonly used to treat pain. The device is surgically implanted just above the spine’s dura, in the epidura, where animal studies showed it could appropriately relay signals to the legs and lower extremities.

“What we have uncovered is a fundamentally new intervention strategy that can affect voluntary movement in people with complete paralysis, even years after their injury,” says Susan Harkema, rehabilitation research director at the Kentucky Spinal Cord Injury Research Center at the University of Louisville and the Frazier Rehab Institute.

(MORE: Paralyzed Rats Learn to Walk Again in Rehabilitation Experiment)

The study follows up the success Harkema and her colleagues had with one patient, Rob Summers. Summers had no motor control below the waist but retained some sensation in the lower extremities. He unexpectedly reported that when he thought about moving his leg, he was able to do so while getting stimulation in his spine.

Harkema decided to stimulate three more patients to better understand why that happened to Summers. She didn’t expect them to respond in the same way as Summers did; in fact, she expected them not to respond.

Two of the paralyzed patients, including Kent Stephenson, who was injured in a motocross accident, had no motor control and no sensation in the lower chest and legs. Harkema wanted to test her theory that Summers’ movement was due to remaining nerve connections in his damaged spinal cord that were somehow reawakened by the electrical stimulation.

Because Summers retained some sensation, Harkema figured that these nerves were being redirected to control some movement. She expected Stephenson not to respond at all to the stimulation, since he had no sensation remaining.

“I was the person who was supposed to go through the experiment and not move, and that was going to justify why Rob moved,” says Stephenson. “I was O.K., and at peace about that as my next thing to do, since the doctors told me I would never move my legs again and never feel my legs again.”

(MORE: Meanwhile, in the Lab …)

The first time the stimulator was turned on after it was implanted, however, Stephenson happily proved Harkema’s original theory wrong.

“The minute I tried to move my left leg, I felt a charge go down my leg and it pulled back just the way I was thinking [to move it],” Stephenson says. “I had done this test a handful of times before and nothing worked — it was boring. But it worked this time. And when I thought about relaxing my leg, it went back down. Everybody in the room went, ‘Whoa.’ My mom was in the room and she burst into tears. I was emotional myself.”

The same thing happened with the remaining two patients; all were able to voluntarily move their legs, feet and ankles within a week of starting the electrical stimulation.

Until these studies, researchers believed that the brain was the master orchestrator of movement, sending the appropriate signals to the spinal cord and helping to direct which signals the spinal cord relayed on to muscles in the legs or arms. But the latest results suggest the spinal cord may be more involved in processing movement than previously thought — the brain still needs to send signals to guide movement, but the spinal cord may be directing and processing neural messages even further.

Thus, focusing on restoring the spinal cord’s integral role in paralyzed patients may be an exciting new way to bring some movement back to them — even years after injury. All four of the patients in the study had been paralyzed for more than two years before they began the stimulation.

Harkema and her colleagues were also able to show that the movements were not just the reflexive responses from electrically stimulating individual nerves that control, say, a toe or ankle. This movement was more systemic, involving the brain and the central nervous system, which runs along the spinal cord. Not only could the patients move the appropriate muscle when they thought about it, but they could also move them when given visual or auditory cues, meaning their brains were processing the commands and relaying the information to the spinal cord for execution.

Harkema stresses that the patients aren’t walking — but they are able to move muscles that were previously lost to them because of their spinal-cord injuries. And that’s an important first step in understanding how to treat paralysis. She also says it’s not clear what role the intense physical therapy the patients received prior to getting the implants played in their responses. In animal studies, physical therapy alone — training animals in harnesses to step, for example — did, over time, teach the animals to step independently.

“It’s possible that the training optimized them to move once the stimulator took them up another notch,” she says. “But we don’t know for sure since we haven’t tried someone who has never been trained before getting the stimulation.”

The fact that the three patients responded almost immediately to the electrical stimulation does hint, however, that physical training isn’t the only factor involved in the restoration of movement in these patients, and that the electrical stimulation may represent an untapped and promising way to treat paralysis.

“The outcome of four out of four patients showing positive results in response to spinal stimulation is extremely exciting, and proves that it’s no longer just an anomaly,” says Grace Peng, program director for the National Institute of Biomedical Imaging and Bioengineering, which funded the study. Peng says the institute is supporting other studies on how such stimulation can treat paralysis, including studies on more flexible stimulators — for now, patients need to set the device to settings to target specific muscles and can only move one region at a time — and stimulators that can be adhered directly to the skin.

For now, however, Harkema is planning to follow up her results with more patients. And Stephenson is enjoying his ability to move, even if it’s limited. After figuring out that setting the stimulator allowed him to concentrate on his abdominal and lower back muscles, he went white-water rafting last summer with his father, cousins and uncle.

“It was an hour-and-a-half float trip, and we were doing 360s along some rapids,” he says. “It was cool!”

Contact us at letters@time.com.