Researchers Identify Neurons That Might Help Paralyzed People Walk Again

Nine people paralyzed by severe spinal cord injuries regained the ability to walk, thanks to a combination of electrical pulses to the lower spine and physical therapy, reports a study published this month in the journal Nature.

The paper builds on work from 2018 that helped three people walk again. But this time, researchers have identified the neurons that might be responsible. Their findings, which looked at neurons in mice, could eventually help scientists develop more sophisticated methods of treatment for humans, per HealthDay’s Amy Norton.

The research “is finally getting at the important contributors to recovery,” Sarah Mondello, a neuroscientist at the University of Washington who did not contribute to the findings, tells Science’s Claudia López Lloreda.

Severe spinal cord injuries can break up the line of communication between the brain and the neurons in the lower spine responsible for walking. Researchers first used electrical stimulation of the lower spine, called epidural electrical stimulation (EES), to treat pain in people with spinal cord injuries, writes New Scientist’s Carissa Wong.

But over the past decade, EES has helped a small number of paralyzed people stand or walk, per HealthDay News. Combined with physical therapy, EES can also help people regain bladder and bowel function and engage in sexual activities, according to Science.

“We mimic the way the spinal cord is normally activated by electrical signals from the brain when you walk, by electrically stimulating the right spot of the spinal cord at the right time to move leg muscles,” Jocelyne Bloch, a neuroscientist at the University of Lausanne in Switzerland and co-author of the paper, tells New Scientist.

In the new study, nine participants with similar spinal cord injuries received implants of the electrical devices. At the start, three participants couldn’t feel or move their legs, and the others had some feeling but little to no movement.

But after five months of treatment, all nine could take steps, and four people could walk without the EES, per Nature News’ Dyani Lewis.

To determine exactly how the electrical stimulation worked, the team performed the same experiment on mice. They paralyzed the hind legs of the mice for the research, according to New Scientist. Using EES and physical therapy on a treadmill, the mice also regained the ability to walk. A computer program revealed a particular type of neuron in the spinal cord that appeared to play a key role, per Science.

When the researchers then blocked the activity of these neurons in the injured mice, the mice did not relearn to walk. But doing so in healthy mice had no effect on their walking, so the researchers concluded these neurons might help with recovery, per Science.

The same neurons likely play the same role in humans, because humans and mice have similar spinal architectures, Eiman Azim, a neuroscientist at the Salk Institute for Biological Studies who did not contribute to the study, says to Nature News. Azim co-authored an opinion piece in Nature accompanying the new paper.

Grégoire Courtine, a co-author of the new study and a neuroscientist at the Swiss Federal Institute of Technology, tells Science that there are probably other types of neurons that might also play an important role in recovery.

The findings could also help researchers identify types of neurons that aid in recovering other functions, Mondello tells Science. Marc Ruitenberg, a neurologist at the University of Queensland in Australia who did not contribute to the research, tells Nature News that it would be interesting to see if the technology could help with bladder, bowel and sexual function, which can improve quality of life more than walking.

Greg Nemunaitis, who did not contribute to the research and is director of spinal cord injury rehabilitation at the Cleveland Clinic, tells HealthDay that recovered functioning in the nine patients in the study is “fantastic,” and that the research on mice is “a first step in understanding and enhancing function in humans.”

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.