Paired corticospinal-motoneuronal stimulation and exercise after spinal cord injury

CONTEXT: Rehabilitation after spinal cord injury (SCI) relies on the use of exercise training, which has limited functional gains. There is a need to develop more efficient approaches to facilitate recovery after SCI. METHODS: This review focuses on a neuromodulation method where transcranial magnetic stimulation (TMS) over the primary motor cortex is paired with transcutaneous electrical stimulation over a peripheral nerve to induce plasticity at corticospinal-motoneuronal synapses. These two stimuli are applied at precise inter-stimulus intervals to reinforce corticospinal synaptic transmission using principles of spike-timing-dependent plasticity applied alone or in combination with exercise training. RESULTS: Transmission in residual corticospinal axons, assessed using TMS and maximal voluntary motor output, increased after stimulation combined with exercise training in persons with SCI. There were also significant improvements in functional outcomes, including walking speed and grasping function, which persisted after 6–9 months post stimulation. Moreover, the data suggested that the effects of the stimulation protocol can be augmented with a higher number of sessions and with multiple stimulation sites in the spinal cord. CONCLUSIONS: Voluntary movement is enhanced in people with SCI through the strengthening of corticospinal-motoneuronal synapses using paired stimulation. This neuromodulation technique represents a novel powerful strategy to facilitate functional recovery after SCI.