Three men who were paralyzed from the waist down are able to walk again with a new type of therapy that uses electrical stimulation, scientists announced today. More than four years prior, the men had all suffered major spinal cord injuries that left them with limited or no movement in their legs.
Researchers in Switzerland applied stimulation to the men’s spinal cords with a wireless implanted device that emits pulses of electricity. Within a week, the men could stand up and walk using supports. After five months of physical therapy and training with the technology, all three were able to voluntarily control their leg muscles and walk for as long as an hour without muscle exhaustion.
The results, published in the journal Nature, come on the heels of two reports last month of similar therapies that were able to help people with major spinal cord injuries walk for the first time in years. A team at the University of Louisville reported in September that stimulating the spinal cord—known as neurostimulation—allowed two people to stand independently and walk with assistive devices, like a walker. In a separate study published the same day, researchers at the Mayo Clinic showed that they had achieved similar results in another person.
In the first two reports, the implants were preset to certain patterns of stimulation. In the latest study, senior author Grégoire Courtine, a neurologist at the Swiss Federal Institute of Technology, developed a mobile app so that the stimulation could be controlled in real-time with a tablet. Such a device could give patients the ability to control the therapy at home outside of a research setting, Courtine says.
The handful of results “is giving us a lot of confidence that this solution is real and even people with complete paralysis can regain stepping movements,” says Chet Moritz, an associate professor of rehabilitation medicine at the University of Washington, who wrote an accompanying editorial in Nature about the most recent findings.
Most people don’t have to think about walking. Our brains do the work for us, sending messages down the spinal cord—a major channel of nerve cells in the body—to the leg muscles. That communication process is blocked in people with major spinal cord injuries, because the nerves along that channel are damaged.
But scientists have been hopeful that these nerve pathways in the spinal cord can be repaired by tapping into certain populations of nerve cells, called neural circuits, that are found in the spinal column. These circuits also lead to the target muscles, but their signals aren't blocked by injuries, so some treatments seek to stimulate the ones below the injury site.
“These neural pathways are by and large still intact and viable,” says Chad Bouton, the director of the Center for Bioelectronic Medicine at the Feinstein Institute for Medical Research in New York, who wasn’t involved in the latest study. “If you could stimulate those, you could try to cause movement.”
In Courtine’s study, the three participants got 16 small electrodes implanted on the lower portion of their spinal cords. Each electrode was precisely placed to activate a specific group of leg muscles. The electrodes connected to a small device surgically placed in the abdomen that generates the electrical pulses. This device, manufactured by Medtronic, is already on the market for deep brain stimulation for Parkinson’s disease. The men also received two wearable sensors, one on each foot, that delivered additional stimulation.
Surprisingly, even when the stimulator was turned off, two of the three participants were able to control their leg muscles on their own. That suggests the stimulation might be rewriting the connections between the brain and spinal cord, Moritz says. At some point, it might be possible to recover those nerve connections enough that stimulation is no longer needed.
“We think the stimulator is acting like a hearing aid or an amplifier for the spinal cord,” Moritz says. “It’s turning up the volume, turning up the excitability of the spinal circuits below the injury.”
However, neurostimulation for paralysis is still in its early stages, and scientists don’t know exactly how it works to restore movement, says Kristin Zhao, an investigator at the Mayo Clinic and author of one of the September papers.
“The thought is that somehow there’s a command coming down from the brain telling the lower limbs to move, and somehow the stimulation is enabling that,” she says. Right now, researchers are experimenting with different patterns, lengths, and intensities of stimulation to get the best results.
Courtine and his team used the tablet to turn the pattern of stimulation on and off depending on where the participants’ feet were in relation to the ground. They think this real-time triggering stimulation might be better than continuous stimulation. In a second paper also published today in Nature Neuroscience, Courtine’s group found that the latter type of stimulation might disrupt a person’s sense of where their legs are in relation to their body, or what’s known as proprioception.
While the results are exciting, it’s important to keep in mind that paraplegics have other needs that go beyond walking, Moritz adds. A 2004 survey conducted by Kim Anderson, a professor at the Case Western Reserve University, showed that walking is not the top priority for people with major spinal cord injuries. Walking actually came in fourth, behind sexual function, bladder and bowel movement, and the ability to control body posture.
Luckily, the emerging types of neurostimulators are showing some signs that they may be able to help restore such functions, as well. But for now, the stimulators are only being used in a small number of patients in research settings. In the future, Courtine thinks such stimulators could be most effective in restoring muscle movement if they are used as soon as possible after an injury.