Enhancing recovery after traumatic brain injury and spinal cord injury by stimulating raphe nuclei in the brainstem

Most commonly used neuromodulation strategies, such as the DBS for treatment of Parkinson’s disease or spinal stimulation for chronic pain, use electrical stimulation to mask or override abnormal firing in disease-affected neuronal networks rather than to assist in repairing these networks.  In other words, the electrical stimulation is used to treat the symptoms rather than the disease itself. In contrast, two publications (one and two) by Dr. Hentall’s group at The Miami Project to Cure Paralysis describe a novel therapeutic role for electrical stimulation in the brainstem, a region of central nervous system between the brain and spinal cord. Specifically, the electrical pulses were used to stimulate activity of the raphe nuclei, which have an important role in orchestrating anti-inflammatory and neuroprotective effects throughout the central nervous system.  The raphe nuclei are composed primarily of serotonergic neurons that have extensive connections throughput the central nervous system, with the raphe magnus projecting to the spinal cord and medial/dorsal raphe nuclei projecting to cerebral cortex and subcortical structures. Due to a high concentration of serotonergic neurons in these nuclei and their common involvement in anti-inflammatory and neuroprotective functions, generalized stimulation of these nuclei results in synergic activation of these neurons and effective induction of biological repair mechanisms. It should be noted that presence of such homogenous neuronal population in the raphe nuclei is rather unique, as most brain regions have heterogenic populations with divergent (sometimes even opposite) functions.