Spinal cord injury (SCI) leads to functional deficit that doesn’t improve over time. Long standing view in the field of neurorehabilitation is that little to no recovery is possible after adult mammalian SCI. However, there is evidence that significant spontaneous recoveries in motor, sensory or other neurological functions occur after SCI in human. The existence of spontaneous recovery raises the possibility that intrinsic structural rearrangement are occurring after SCI. Previous studies suggest that SCI induces axonal sprouting and this injury-induced plasticity is correlated with functional recovery. Moreover, based on activity-dependent plasticity and the fact that some descending motor axons are usually spared by injury, electrical stimulation of the unimpaired side of the brain has been found to strengthen the spared CST connections and improve functional recovery after CST injury. However, the mechanisms underlying spontaneous recovery after cervical contusion SCI is not known, and it has never been shown that the spontaneous or enhanced functional recovery is specifically mediated by the sprouting axons. Thus, in this study, the circuits responsible for spontaneous forelimb motor recovery after cervical hemicontusion SCI will be identified with viral tracers. The identified circuit will be strengthened and recovery of skilled forelimb function will be promoted after chronic cervical SCI with motor cortex stimulation. Finally, the causal relation between sprouting and functional recovery after SCI will be addressed by using pathway-specific inactivation technique.
1. Axon sprouting from the largely spared ipsilateral CST mediate spontaneous recovery of forelimb function after cervical contusion SCI.
2. Electrical stimulation to motor cortex will augment cortically-evoked muscle responses and functional recovery through double-crossed CST connection.