Zapping specific neurons helps people walk again after spinal injury

After receiving electrical stimulation to the spine, nine people with lower body paralysis improved their ability to walk, and researchers then mapped the neurons that appeared to have promoted this recovery.

After receiving prolonged electrical stimulation to the injured area of their spine, some people with lower body paralysis can walk further. Jimmy Ravier, NeuroRestore

After receiving prolonged electrical stimulation to the injured area of their spine, nine people with varying degrees of lower body paralysis were able to walk. As a result, researchers identified neurons that may aid in the recovery of walking ability after paralysis.

Electrical spinal cord stimulation is frequently used to relieve pain in people with spinal cord injuries. Electrical stimulation also accelerated walking recovery in people with spinal cord injuries who had enough functioning neurons in the affected area, according to the most recent discovery.

"By electrically stimulating the right spot of the spinal cord at the right time to move leg muscles, we mimic the way the spinal cord is normally activated by electrical signals from the brain when you walk," says Jocelyne Bloch of the University of Lausanne in Switzerland.

The team implanted electrical devices into the spinal cords of nine people who had spinal cord injuries in a similar area. Six of the participants could feel their legs but couldn't move them, while the remaining three couldn't feel or move their legs at all.

Artificial intelligence was used to personalize the pattern and location of the pulses delivered to the participants' spinal cords. The participants were then instructed to walk as far as they could in six minutes.

The electrical stimulation enabled them to walk nearly 25 meters on average with the assistance of a frame.

They continued to receive this electrical stimulation, as well as guided physiotherapy sessions, up to five times per week for the next five months. At the end of the study, they could walk 50 meters in about 6 minutes on average.

Four of the participants were able to walk without any electrical stimulation, indicating that the therapy resulted in long-term rewiring of spinal cord neurons.

To learn more about how this happened, the researchers inflicted spinal cord injuries on mice, paralyzing their hind legs. They then implanted a device in the animals' spines that delivered electrical pulses. Their walking ability gradually improved.

The researchers then mapped the gene activity of neurons at the spinal injury site of the mice, which revealed that a specific type of neuron became more active after electrical stimulation.

They then used a light-controlled genetic tool to silence and reactivate the neurons associated with walking recovery. When the neurons were turned on, the rehabilitated mice could only walk.

"After a spinal cord injury, there is a lot of chaotic activity with a lot of neurons trying to function," Bloch says. "The electrical rehabilitation organizes the cell network, and you actually increase the activity of a specific type of cell while all other cells are not activated."

The researchers also discovered that silencing these neurons in non-paralyzed mice had very little effect on their walking ability.

"These cells are important for walking recovery in injured mice, but when we turned them off in healthy mice without injury, it had little effect on their ability to walk," Bloch says.

In an accompanying opinion piece, Kee Wui Huang and Eiman Azim of the Salk Institute for Biological Studies in California wrote, "The identification of a recovery-organizing cell type is a big step forward in our understanding of the mechanisms that underpin [electrical stimulation] rehabilitation."

Manipulation of these neurons in the future may reveal new ways to improve walking ability after paralysis. Huang and Azim penned the piece.

Journal citation: Nature, DOI: 10.1038/s41586-022-05385-7 


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