Electrical stimulation of the spinal cord can help recover mobility in some paralysed patients. However, the mechanism underlying this partial recovery of function remains unknown. A recent human study has confirmed the involvement of a group of cells previously identified in mice, paving the way to targeted treatments.
In a recently published study in Nature 1, researchers modelled the electrical stimulation paradigm used in humans and called epidural electrical stimulation (EES) in mice, in which they identified the responsible cell population. Then, later on, they proved that this was the correct population by directly stimulating these cells in nine partially or completely paralysed patients who experienced an improvement in motor function (aka walking). Interestingly, this improvement was maintained after the 5 months of rehabilitation and EES treatment, even without stimulation.
To identify the neuron population responsible for this recovery of motor activity, the researchers used a map of genetic expression of neurons in the spinal cord and in combination with the functional EES data identified V2a neurons as the ones allowing patients to walk again. These neurons express the gene Vsx2, and although not involved in walking before spinal cord injury, they become fundamental in the recovery of movement after spinal cord injury.
If you feel like there are a lot of unanswered questions, it is because there are. This is a first step in the right direction which may allow more targeted EES treatment in affected patients, but clearly V2a neurons do not work alone for recovering function in the patients’ legs, so further research should focus on identifying other involved neuron populations which may be critical as well for recovery.