Restorative Neuromodulation for Upper Extremity Functions

Spinal cord is composed of specialized neural networks, capable of executing different functions. Although the command for upper-limb functions such as reaching and grasping is delivered from the brain, the cervical spinal cord circuits work as an important hub for not only executing the task, but also amplify the command and maintain the dynamics with proper feedback mechanisms with it's reflex circuitry. A simple reaching and grasping function requires spatiotemporal coordination of upper-limb joints and the neuromuscular systems, their adaptation and control in gravity. For human, these physiological activities are well choreographed by sets of neural networks. In combination with afferent sensory inputs, these network circuits work with the motor periphery to generate a series of motor acts during each task. Normally, the activity of these spinal networks are regulated supraspinally and by peripheral sensory inputs. In case of the loss of supraspinal inputs, resultant of a traumatic brain injury (TBI) or cervical spinal cord injury (SCI), upper-limb motor tasks maybe enabled by directly activating these specialized cervical cord networks via external stimuli. Recent studies have demonstrated that neuromodulation via spinal cord stimulation can effectively restore upper-limb motor function in patients with chronic neurological injuries. Traumatic injuries to the central nervous system (CNS) such as TBI and SCI are devastating events leaving patients with impairment of motor, sensory and autonomic functions. Mainstay for the treatment is still limited to rehabilitation by physical therapy and training. In few patients, however, neuroplasticity and repair mechanisms are considered to contribute to recovery of paresis in the acute stage of the injury and stops in the chronic stage. But, three recent groundbreaking pilot studies have shown that the recovery can be further amplified in the chronic stage by the novel treatment of trans-spinal electrical stimulation. However, the rehabilitation related to this recovery is not well understood, and thus it is a challenge to be convinced with the efficacy of this new therapy. A deeper understanding of the physiology in a larger trial of two different but related neurological patient groups, proposed in this study, will significantly help the researcher to prove the efficacy and understand the mechanism of trans-spinal electrical stimulation therapy for the patients. This study will further assist the researchers to design even a better therapeutic intervention for neurological impaired patients.