Misappropriated neurons: new hope for people with spinal cord injury

Severe spinal cord injuries often result in the loss of the connection between the brain and the nerve cells in the lower spine that control walking. The motor, sensory and vegetative functions under the interruption may then fail completely or partially, affecting the quality of life of those affected: they suffer from paralysis, sensory loss and health problems such as poor blood pressure control, incontinence and an increased risk of infection. With the current state of medicine, complete spinal cord injury is irreversible.

A new experimental therapy, which is only suitable for some of those affected, gives hope to patients with spinal cord injury: electrode implants in the spinal cord activate trunk and leg muscles and thus enable them to walk supported on walkers. This was reported by a research team from the Swiss Federal Institute of Technology in Lausanne (EPFL) led by Jocelyne Bloch and Grégoire Courtine in February this year in the journal “Nature”.

Electrical impulse stimulation (ESS) of the spinal cord had long been used to treat chronic pain, but Bloch and Courtine had adapted the technique to people with spinal cord injury. As early as 2018, they showed patients who could still move their legs or feet minimally that this works in principle. This allowed them to improve their method and also successfully test it on patients who no longer had residual mobility. Other research teams have also succeeded in partially reversing paralysis by electrically stimulating the spinal cord below the injury.

The team in Lausanne implanted an electrical stimulator in the patients that stimulates the dorsal roots. Sensory signals enter the spinal cord through these posterior nerve roots. The electrodes that deliver the electrical impulses were connected to an impulse generator, which in turn can be controlled wirelessly via a tablet computer. The patients were also put on a stretcher so that their legs could move.

After five months of intensive training, the patients were able to walk a certain distance independently again with a walking aid. However, until now it has remained completely unclear how this progress came about in detail.

Bloch and Courtine have now gained more insight in a new study published in the journal Nature. The study of the EES-treated patients and similarly treated mice showed that the success of EES therapy is based on certain nerve cells. Using a computer algorithm, the researchers were able to identify those neurons that change after spinal cord injury and electrical stimulation.

It is a specific group of so-called interneurons, which are remarkably not involved in movement in healthy individuals. However, they are indispensable for electrostimulation of the legs after spinal cord injury. If these neurons were destroyed in mice before therapy, the study authors write, the treatment was unsuccessful.

So it seems that these interneurons, which normally process signals rather than transmit stimuli, were abused to some extent: they now connected the neurons of the muscles with signals from the brain. This way the legs could be consciously controlled again.

The scientists now hope that their findings will contribute to the further improvement of epidural electrical stimulation. Despite the successes achieved so far, there are also concerns that this procedure will not be an “early fix for everyone affected by spinal cord injury,” as Winfried Mayr of the Center for Medical Physics and Biomedical Technology at Meduni Vienna explained to the ORF.

Mayr believes that the patients who have made such progress certainly have particularly favorable conditions that are not present in most cases. “Essentially, an appropriate amount of voluntary movement control must have been preserved through the site of the injury,” he explained. According to Mayr, the “solid scientific result” should not be discounted, but expectations should not be raised either, “which cannot be fulfilled for the time being”. (i.e)