Thanks to electrical stimulation of the spinal cord, nine people with a paralyzed lower body were able to walk somewhat again. Researchers have now discovered which neurons are responsible for this recovery.
Earlier this year, nine people with varying degrees of lower body paralysis Learn to walk behind a walker again. They were able to do this thanks to long-term electrical stimulation of the affected part of their spinal cord. Now have researchers identified the neurons believed to help restore walking ability after paralysis.
Electrical stimulation of the spinal cord is often used to relieve pain in people with spinal cord injury. The method can also speed up walking recovery. When you walk, your spinal cord is usually activated by electrical signals from the brain. We mimic that method by using electrical signals to stimulate the right place in the spinal cord at the right time to move the leg muscles,’ says neuroscientist Jocelyne Bloch from the University of Lausanne in Switzerland.
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Permanent rewiring
Bloch’s team implanted an electrical device into the spinal cords of nine people who all had injuries in roughly the same area of the spinal cord. Six of the participants had some feeling in their legs, but could hardly move them. The remaining three could not feel or move their legs at all.
The spinal cord of the participants was electrically stimulated with the device. The pattern and precise location of the pulses was individually determined for each patient via artificial intelligence. The participants were then asked to walk as far as they could in six minutes. Using a rollator, they were able to walk an average of almost 25 meters per person thanks to the electrical stimulation.
For the next five months, the participants continued to receive the electrical stimulation up to five times a week. These sessions were accompanied by targeted physiotherapy. At the end of that period, they could walk an average of 50 meters in six minutes.
Four of the participants were able to walk even without prior electrical stimulation at that time. This indicates that the therapy produces a permanent rewiring of the spinal cord neurons.
Mice
To better understand how this happens, the researchers induced spinal cord injury in mice. In doing so, they paralyzed the hind legs of the animals. Then they implanted a device in the mice that sent electrical impulses to their spines. This led to improved walking ability.
The researchers then studied the gene activity of the neurons in the mice at the site of the spinal cord injury. This showed that a certain type of neuron became more active after electrical stimulation.
Finally, the researchers used a genetic tool that is controlled by light. This enabled them to turn off and reactivate the neurons associated with gait recovery. The rehabilitated mice turned out to be able to walk only when the neurons were turned on.
Big step
‘After a spinal cord injury you have to contend with chaotic activity of many neurons, all trying to function,’ says Bloch. ‘The electrical rehabilitation reorganizes the network of brain cells. You increase the activity of a specific type of cell, while all other cells are not activated.’
The researchers also found that turning off these neurons in mice that were not paralyzed had little effect on their ability to walk. ‘These cells are important for the recovery of walking in mice with paralysis. But if we knock them out in healthy mice without injury, it hardly affects their ability to walk,’ says Bloch.
“The identification of a repair-organizing cell type represents a major advance in our understanding of the mechanisms underlying electrical stimulation rehabilitation,” neurobiologists write. Kee Wu Huang and Eiman Azim from the Salk Institute for Biological Studies in California in a accompanying opinion article in Nature. In the future, manipulation of these neurons could yield new ways to improve walking ability after paralysis, they write.