We now know why electrical stimulation helps people walk again

Identifying Nerve Cells Responsible for Rehabilitation of Paralysed People with Spinal-Cross Instability Using Electroencephalograms

Neuroscientists have identified the nerve cells responsible for helping paralysed people to walk again, opening up the possibility of targeted therapies that could benefit a wider range of people with spinal-cord injuries1.

“The amount of hope that it gives to people with spinal-cord injury is incredible,” says Marc Ruitenberg, a neurologist at the University of Queensland in Brisbane, Australia, who studies spinal-cord injury.

The overall decrease in neural activity at the site during rehabilitation reflects a learning process, says Courtine. He says there is less and less neurons activated in the brain when you get better at a task.

Technology doesn‘t exist to gather this kind of direct evidence in people. But Eiman Azim, a neuroscientist at the Salk Institute for Biological Studies in La Jolla, California, says the same neurons are probably responsible for the effect, because spinal architecture is very similar across vertebrates, including humans and mice.

The use of EES to restore arm movements and hand grip in monkeys has been done before by Courtine and his colleagues. And a group at the University of Washington in Seattle has done the same for six people with spinal-cord injuries, using non-invasive electrode-bearing skin patches placed on the neck6.

Courtine says that identifying the nerves responsible for these functions is on his list of next steps now that he has a detailed molecular map to work with. He has also launched a start-up company — ONWARD, based in the Netherlands — to commercialize the technology. The company will begin recruiting people in the United States in a few years.

“This is very exciting,” says Jason Carmel, a motor system neuroscientist at Columbia University who wasn’t involved in the study. “It opens up a potential treatment avenue that we’ve never had before for people with chronic stroke.”

A stroke is caused when the brain’s blood supply is blocked. Depending on the severity of the brain damage, a stroke can cause impairments, such as paralysis, weakness, or problems with speaking, thinking, or memory.

People with paralysis from stroke can’t move a certain muscle or group of muscles voluntarily. When the part of the brain that controls movement is damaged, there is a change in the way the brain and the muscles communicate. Patients who recover often do so within the first few months after a stroke. Beyond six months, there’s little chance of further improvement. This is the chronic stage of stroke, when effects are usually permanent.

The researchers hope to deliver electricity to nerve cells in the spine. The electricity makes these nerve cells more responsive, or excitable, which helps signals from the brain get through to the muscles they control.

Spinal cord stimulation is already used as a treatment for pain, and in 2018, separate research teams published a series of papers showing that it allowed a handful of patients paralyzed from spinal cord injuries to stand independently and walk with assistive devices for the first time in years. But spinal cord stimulation for upper-limb recovery has been largely unexplored.

The day researchers turned the electrical stimulation on, Rendulic was able to fully open and close her left hand—something she couldn’t do before. She says they were all in tears. “I was opening my hand in ways I hadn’t in almost a decade.”

The treatment results will need to be replicated in a larger study to see which patients benefit the most from it.

Learning to move and eat with her hand using pulse-based functional outputs: A case study of Rendulic’s control of the arm and hand

Rendulic liked to ride horses as a teenager. Then, beginning in 2011, she had a series of strokes caused by malformed blood vessels in her brain. The last stroke was the worst.

She was able to move her arm and hand. She could close her hand, but not open it. She couldn’t open a jar, or chop vegetables because she couldn’t tie her shoes.

“We wanted to pick up on these weak signals and essentially turn them into functional outputs so that a person would be able to control their own hand voluntarily,” he says.

Elvira Pirondini, a research assistant professor of physical medicine and rehabilitation, said that at first she could not really do anything with her hand. She can get to the soup when the stimulation is on, as well as grab the can and elevate it.

Also, the effects diminished but did not disappear entirely when the stimulation was switched off. That suggests the pulses are causing changes to the circuits controlling the arm and hand, Capogrosso says, though it’s not clear how long those changes will last.

At the end of the four-week study, the electrodes were removed from both patients. Researchers are planning to develop a permanently implanted system.

This sort of technology takes many years to move from the lab to widespread use. But the process is likely to move much faster in this case because the device used to stimulate the spine is already approved by the Food and Drug Administration for treating patients with chronic pain.

Rendulic hopes to be the first in line to get a permanently implanted stimulator, as she says her experience has changed how she views her future.

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