Using a mixture of electrical stimulation and vigorous physical therapy, nPeople with chronic spinal injuries have had their ability to walk restored.
All suffered from severe or complete paralysis as a result of damage to their spinal cord. Incredibly, all volunteers saw improvements immediately and continued to show improvements five months later.
A recent study by researchers from the Swiss research group NeuroRestore identified the exact neural groups stimulated by the treatment, using mice as a starting point.
The nerve cells that orchestrate walking are located in the section of the spinal cord that runs down our lower back. Injuries to our spinal cord can interrupt the chain of signals from the brain, preventing us from walking even when those particular lumbar neurons are still intact.
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Unable to receive commands, these “walking” neurons become essentially non-functional, potentially leading to permanent paralysis of the legs.
Previous research has shown that electrical stimulation of the spinal cord can reverse such paralysis, but how this happened was not clear. So neuroscientist Claudia Kathe from the Swiss Federal Institute of Technology in Lausanne (EPFL) and her colleagues tested a technology called epidural electrical stimulation in nine people, as well as in an animal model.
The spinal cord was stimulated by a surgically implanted neurotransmitter. Meanwhile, the patients also underwent an intensive neurorehabilitation process that included a robotic support system that assisted them while moving in multiple directions.
Patients spent five months of stimulation and rehabilitation, four to five times a week. Amazingly, all the volunteers were then able to take steps with the help of a walker.
To the researchers’ surprise, the recovered patients actually showed a decrease in neural activity in the lumbar spinal cord during walking. The team believes this is due to improved activity in a specific subset of neurons necessary for walking.
“When you think about it, it shouldn’t be a surprise,” Courtine told Dyani Lewis on Nature“because in the brain, when you learn a task, that’s exactly what you see – fewer and fewer neurons fire” as you get better at it.
So Kathe and team modeled the process in mice and used a combination of RNA sequencing and spatial transcriptomics—a technique that allows scientists to measure and map gene activity in specific tissues—to figure out which cells were doing what.
They identified a single population of previously unknown neurons that can take over after an injury, found in the intermediate laminae of the lumbar spinal cord.
This tissue, made up of cells called SCVsx2::Hoxa10 neurons, do not appear to be needed for walking in healthy animals, but appear to be essential for recovery after spinal cord injury, as their destruction prevented the mice from recovering. However, their recruitment depends on the activity.
SCVsx2::Hoxa10 Neurons are “uniquely placed” to convert information from the brainstem into executive commands. These are then transmitted to the neurons responsible for producing walking, Kathe and colleagues explain in their paper.
This is only one component of a very complex chain of messaging and receiving cells, so much remains to be explored.
However, “these experiments confirmed that the participation of S.KVsx2::Hoxa10 Neurons are a fundamental requirement for the recovery of walking after paralysis,” the researchers concluded.
This new understanding could eventually lead to more treatment options and may provide a better quality of life for people with all kinds of other spinal cord injuries as well.
Their research was published in Nature.
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