The World Health Organization (WHO) estimates that half a million people experience spinal cord injuries (SCI) every year. Researchers at the Center for Neuroprosthetic and Brain Mind Institute in Switzerland reported that approximately half of human spinal cord injuries lead to paralysis severe enough to keep the person in a wheelchair for the rest of his or her life. An incomplete spinal cord injury is sufficient to cause severe motor impairments, but a few nerve fiber bridges remain. Can researchers figure out a way to repair these paths and help the patient regain functional movement after spinal cord injury?
There are a few new avenues of research being worked on that need further exploration. In the lab of Dr. Gregoire Courtine, they are using these spared fibers to restore locomotor by increasing the movement control commands that are carried by these remaining intact circuits. The lumbar spinal cord has a locomotor central pattern generator (CPG) that produces rhythmic output without sensory or motor feedback from muscle targets. Spinal cords that have been isolated from the body can still produce activity patterns associated with locomotion. However, to initiate movement they need input from the brain.
Much of the research in SCI so far has focused on promoting the growth of interrupted axons and fibers to reconnect the supraspinal (above the spinal cord) motor cortex to neurons below the site of injury. This type of recovery would depend on making new circuit formations in acute injuries that still have plasticity. It is even more challenging to restore locomotion in chronic paralysis.
In a study published in Science Translational Medicine, researchers tried to reactivate these inactive circuits below the lesion in rats with chronic, severe, and incomplete SCI. They found locomotion can be initiated by the midbrain, the brainstem, and the spinal cord. These results show an area that can give rise to movements independent of the frontal cortex. Deep brain stimulation in the mesencephalic locomotor region (MLR) of rats with severe spinal cord injury immediately improved locomotor performance in the previously paralyzed hindlimbs on the rats. The results of this study suggest that excitatory stimulation in the MLR by deep brain stimulation could be key to improving gait and locomotion.