Comparing the effects of functional electrical stimulation versus somatosensory stimulation on increasing corticospinal excitability for a muscle of the hand

Cameron S Mang, Joanna M Auger, David F Collins


The electrically-evoked afferent volley generated during neuromuscular electrical stimulation (NMES) can increase the excitability of corticospinal (CS) pathways. Over time, NMES can strengthen damaged CS pathways and result in enduring improvements in function for persons with central nervous system injury or disease. NMES-induced increases in CS excitability have been studied using a variety of NMES parameters, yet the influence of these stimulation parameters on increasing CS excitability is not well-defined. Typically, NMES is either delivered at intensities sufficient to generate repeated functional contractions for relatively short durations (30-40 min) or at low intensities, near motor threshold, for long durations (2 h). For the purpose of this study, these different stimulation protocols are termed functional electrical stimulation (FES) and somatosensory stimulation (SS), respectively. A direct comparison of increases in CS excitability induced by such protocols has not been conducted. Thus, the present experiments were designed to compare changes in CS excitability for abductor pollicis brevis (APB) in the hand following FES and SS of the median nerve. We hypothesized that due to the generation of a larger afferent volley, the FES would increase CS excitability more than the SS. Ten motor evoked potentials (MEPs) were evoked in APB using transcranial magnetic stimulation before and after each type of NMES. MEP amplitude increased significantly following both the FES (by 66 ± 7%) and SS (49 ± 6%), but the amplitude of these increases was not different. These results suggest that just 40 min of FES can increase CS excitability, and provide rehabilitative benefits, to the same extent as 2 h of SS.

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