The Potential of Corticospinal-Motoneuronal Plasticity for Recovery after Spinal Cord Injury

Purpose of Review: This review focuses on a relatively new neuromodulation method where transcranial magnetic stimulation over the primary motor cortex is paired with transcutaneous electrical stimulation over a peripheral nerve to induce plasticity at corticospinal-motoneuronal synapses. Recent Findings: Recovery of sensorimotor function after spinal cord injury largely depends on transmission in the corticospinal pathway. Significantly damaged corticospinal axons fail to regenerate and participate in functional recovery. Transmission in residual corticospinal axons can be assessed using non-invasive transcranial magnetic stimulation which, when combined at the proper time with peripheral nerve electrical stimulation, can be used to improve voluntary motor output, as was recently demonstrated in clinical studies in humans with chronic incomplete spinal cord injury. These two stimuli are applied at precise inter-stimulus intervals to reinforce corticospinal synaptic transmission using principles of spike-timing-dependent plasticity. Summary: We discuss the neural mechanisms and application of this neuromodulation technique and its potential therapeutic effect on the recovery of function in humans with chronic spinal cord injury.