Nine persons with persistent spinal injuries were able to regain their capacity to walk thanks to a combination of electrical stimulation and rigorous physical therapy (NeuroRestore).
All had spinal cord injuries that left them with severe or total paralysis. Amazingly, the participants all experienced gains right away, and they persisted through five months.
Using mice as a starting point, current research by scientists from the Swiss research team NeuroRestore has pinpointed the precise neuron groups triggered by the therapy.
The portion of the spinal cord that runs through our lower backs contains the nerve cells responsible for controlling walking. Even when these particular lumbar neurons are still intact, injuries to the spinal cord can stop the brain's chain of messages from reaching our legs, stopping us from walking.
These "walking" neurons basically stop functioning when they are unable to receive orders, which could result in a permanent paralysis of the legs.
Previous studies had shown that electrical stimulation of the spinal cord may cure this paralysis, though it wasn't apparent how. Thus, epidural electrical stimulation was put to the test on nine people and an animal model by neuroscientist Claudia Kathe of the Swiss Federal Institute of Technology Lausanne (EPFL).
A neurotransmitter that was surgically placed activated the spinal cord. Patients also underwent intense neurorehabilitation, which includes moving in various directions with the aid of a robotic support device.
Four to five times each week for five months, the patients underwent stimulation and rehabilitation. Amazingly, after that, all of the volunteers could walk with a walker.
To the surprise of the researchers, walking reduced the neuronal activity in the lumbar spinal cord in the healed individuals. The research team theorizes that this occurs as a result of the activity being focused on a certain subset of neurons required for walking.
Because in the brain, when you learn a skill, you notice that there are less and less neurons active as you grow better at it, Courtine told Dyani Lewis of Nature, "that should not be a surprise when you think about it."
In order to determine which cells were performing which tasks, Kathe and her team modeled the process in mice and combined RNA sequencing with spatial transcriptomics, a method that enables researchers to detect and map gene activity in particular organs.
They discovered a single population of previously unidentified neurons in the intermediate laminae of the lumbar spinal cord that can take control in the event of an injury.
The SCVsx2::Hoxa10 neurons that make up this tissue don't appear to be necessary for walking in healthy animals, but they do appear to be crucial for recovering from a spinal injury because removing them prevented mice from recovering. However, their recruitment is activity-dependent.
The "unique positioning" of SCVsx2::Hoxa10 neurons allows them to translate brainstem information into executive commands. In their research, Kathe and colleagues describe how they are subsequently transmitted to the neurons that produce movement.
There is still more to be researched as this is simply one link in a very intricate web of messaging and receiving cells.
The participation of SCVsx2::Hoxa10 neurons, however, "was validated by our trials, and is a crucial prerequisite for the resumption of walking following paralysis," the researchers said.
This new knowledge may eventually result in more therapy options and even improve the quality of life for those who have suffered various other spinal cord injuries.
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