Corticospinal Contributions to Lower-limb Muscle Activity after Spinal Cord Injury

Abstract

The corticospinal tract is an important target for motor recovery in humans with spinal cord injury (SCI). Using noninvasive electrophysiological techniques we have demonstrated the presence of reorganization in corticospinal projections targeting spinal motor neurons of lower-limb muscles in individuals with chronic anatomically incomplete cervical SCI. Our physiological findings indicated that corticospinal transmission in leg muscles changes in a task-dependent manner and to a different extent in individuals with and without spasticity. We used a noninvasive stimulation protocol to enhance transmission in residual corticospinal projections in leg muscles in humans with incomplete SCI. Here, we precisely timed the arrival of descending and peripheral volleys at corticospinal-motoneuronal synapses of leg muscles. We found that the arrival of presynaptic volleys prior to motor neuron discharge enhanced corticospinal transmission and leg voluntary motor output after a single and repeated sessions of stimulation. Thus, modulation of residual corticospinal connections may represent a therapeutic target for enhancing lower-limb recovery following SCI.