Testing the feasibility of a corticospinal excitability assessment system

Abstract

To assess the contributions from cortical and spinal structures to motor output, it is necessary to stimulate cortical, thoracolumbar and peripheral nerve structures during voluntary contractions This feasibility study implemented a tri-modal (cortical, thoracolumbar, and peripheral nerve) stimulation protocol during isometric quadriceps contractions of varying levels. The first step consisted in the stimulation of the femoral nerve to obtain the maximal muscle response in the vastus medialis. Subsequently, thoracolumbar and transcranial stimulation intensities that evoked responses equal to 20 percent of the maximal femoral stimulation muscle response were determined. Following the determination of the individual stimulation intensities, cortical, thoracolumbar, and peripheral nerve stimulation were delivered in a pseudorandom manner for all stimulation modalities and muscle contraction levels (25, 50, 75, and 90 percent maximum voluntary contractions) while recording the surface electromyography responses from the vastus medialis. It was possible to run the full protocol of three of the five participants, but further development would allow for future research on corticospinal and spinal excitability.