In 2022, a team led by Grégoire Courtine at the Swiss Federal Institute of Technology published a paper in Nature that identified the specific neurons responsible for restoring walking after paralysis. They called them SCVsx2::Hoxa10 neurons—a population of cells in the lumbar spinal cord that, when activated by epidural electrical stimulation combined with rehabilitation, orchestrated the recovery of walking in nine individuals with chronic spinal cord injury. When the researchers optogenetically silenced these neurons in mice, walking stopped instantly. When they reactivated them, walking resumed immediately. The paper didn’t just show that spinal cord stimulation works. It showed which neurons it works through—a mechanistic explanation for a result that had previously looked like something between a miracle and an engineering trick.
That result sits at the center of a field that has moved, in under a decade, from “we got a paralyzed person to twitch their leg” to “we got a completely paralyzed person to walk, cycle, swim, and climb stairs within 24 hours of turning on the stimulator.” The technology isn’t a cure. It doesn’t repair the severed spinal cord. But it’s the closest thing to functional restoration that exists for the roughly 250,000 to 500,000 people worldwide who sustain spinal cord injuries each year.
How the spinal cord works (and what happens when it breaks)
Your brain doesn’t directly control your legs. It sends high-level movement commands—”walk,” “stand,” “step over that obstacle”—down the spinal cord, where local neural circuits called central pattern generators translate those commands into the precise, rhythmic sequences of muscle activation that produce coordinated movement. The spinal cord below the injury site isn’t dead tissue. The pattern generators, the motor neurons, the sensory circuits—they’re all intact. They’re just disconnected from the brain. A spinal cord injury is less like cutting a power cable and more like cutting the communication line between a command center and a factory that’s still fully staffed and operational.
This is why epidural electrical stimulation works. A thin array of electrodes, implanted on the surface of the spinal cord below the injury site, delivers patterned electrical pulses that mimic the signals the brain can no longer send. The electrodes activate the dorsal roots—the sensory nerve fibers that enter the spinal cord from the body—which in turn excite the spinal circuits that coordinate movement. The stimulator doesn’t replace the brain. It substitutes for the broken communication link, providing enough activation to the intact spinal circuitry below the injury to enable the pattern generators to do what they were designed to do.
What patients can actually do
The results have escalated quickly. In 2018, patients with incomplete spinal cord injuries—some residual sensation or movement below the injury—were able to walk and cycle with epidural stimulation. Courtine’s 2022 Nature Medicine paper pushed further: three patients with complete paralysis—no voluntary movement, no sensation below the injury—could take steps on a treadmill within the first day of turning on the stimulator. One climbed stairs. All could swim, cycle, and perform leg presses. A biomedical engineer at the University of Alberta who reviewed the results called it “a big deal.”
A 2025 case study from Italian researchers at the MINE Lab and EPFL documented the first successful application of epidural stimulation in a patient with a lower thoracic spinal cord injury involving the conus medullaris—the tapered lower end of the spinal cord. Previous trials had excluded these patients, who represent over half of thoracic spinal cord injuries, because of concerns about damaging the nerve roots that control the legs. The patient progressed from being unable to walk to covering one kilometer independently with a walker within six months of the implant. A 2025 paper in Science Translational Medicine showed that high-frequency epidural stimulation reduced spasticity—the involuntary muscle contractions that plague roughly 70 percent of spinal cord injury patients—enabling rehabilitation protocols that further improved recovery.
A systematic review published in 2024 analyzed 64 studies encompassing 306 patients and found improvements in motor function, cardiovascular regulation, pulmonary function, bladder and bowel control, and genitourinary function. The effects extend well beyond walking. Spinal cord stimulation is restoring autonomic functions—blood pressure regulation, temperature control, sexual function—that most people don’t associate with paralysis but that profoundly affect quality of life.
The gap between demonstration and daily life
The results are genuine. The caveats are significant.
First, the stimulator must be on for the abilities to exist. Turn it off, and the paralysis returns. Some patients have shown neural adaptation over months or years of stimulation combined with rehabilitation—one participant in a 2017 study progressively recovered voluntary leg movement and standing without stimulation over 3.7 years of training—but this is the exception. For most patients, the device is a permanent prosthetic, not a temporary bridge to recovery.
Second, the current interface is cumbersome. Users select their desired movement on a tablet, which sends Bluetooth commands to a transmitter worn around the waist. The transmitter must be positioned next to a pulse generator implanted in the abdomen, which activates the electrode array on the spine. Courtine’s team is developing a next-generation system, but the current version requires conscious selection of each movement type before execution. You don’t just decide to walk. You tell the tablet you want to walk, the tablet tells the transmitter, the transmitter tells the implant, and the implant activates the pattern that produces walking. The latency and cognitive overhead are nontrivial.
Third, weight support matters. The patients who stepped within 24 hours did so in harnesses that supported more than half their body weight. The one-kilometer walk with a walker at six months is a more representative picture of functional use than the headline-grabbing first-day stepping videos. And patients with paralysis are at elevated risk for osteoporosis and fragility fractures—bones that haven’t borne weight for years break under loads that healthy bones absorb without issue.
Fourth, the technology doesn’t work equally well for everyone. Severity of the original injury, time elapsed since injury, location of the damage, and the individual patient’s residual neural architecture all affect outcomes. A 2025 study of 11 patients with incomplete injuries found that spasticity improved in all 11, sensation recovered in 10, but only 4 of 11 showed improved lower limb strength. The field is still identifying which patients benefit most and why.
Where it’s heading
The next frontier is closed-loop stimulation—systems that read neural signals from the spinal cord or brain in real time and adjust stimulation parameters automatically, rather than relying on preset patterns selected through a tablet. A 2026 case report from Zhejiang University described a closed-loop spinal neural interface combined with rehabilitation for incomplete spinal cord injury, representing early steps toward systems that adapt to the patient’s intent rather than executing fixed programs.
Intraspinal microstimulation—tiny electrodes inserted directly into the spinal cord rather than placed on its surface—offers potentially more precise and selective muscle activation. A 2026 study in Scientific Reports described the first fully implantable intraspinal microstimulation device tested in a large animal model with spine dimensions similar to humans, moving toward clinical translation.
The broader trajectory: epidural stimulation combined with rehabilitation is progressing from proof-of-concept in research labs to clinical feasibility studies to, eventually, regulated medical devices available to the hundreds of thousands of people living with spinal cord injuries worldwide. The International Neuromodulation Society has published consensus guidance on the safety of epidural stimulation, noting it is “a generally safe, minimally invasive procedure.” The infrastructure for clinical translation is being built.
Courtine’s lab identified the neurons. The Italian team proved it works in injuries previously considered untreatable. The spasticity reduction data from Science Translational Medicine demonstrated benefits beyond motor recovery. The systematic reviews have established the evidence base. What remains is the engineering work of making the system smaller, smarter, more responsive, and cheap enough to deploy at the scale the patient population requires—the same progression from laboratory demonstration to clinical reality that every neuroprosthetic technology follows, measured in years, not months.
We cover spinal cord stimulation alongside brain-computer interfaces, retinal implants, and the full landscape of neuroprosthetic technology across our Neuroprosthetics course—including why the spinal cord below an injury isn’t a broken machine waiting for repair. It’s a working machine waiting for a signal.