Motor Cortex Excitability is Modulated by Cutaneous Electrical Stimulation of the Foot Sole

MOTOR CORTEX EXCITABILITY IS MODULATED BY CUTANEOUS ELECTRICAL STIMULATION OF THE FOOT SOLE Gagandeep Gill Advisor: University of Guelph, 2016 Dr. Leah R. Bent Lower limb peripheral nerve stimulation, which activates cutaneous afferents from the foot dorsum, has been shown to generate transcortical reflex responses. This suggests that the motor cortex may play a role in modulating lower limb cutaneous reflexes. Electrical stimulation of the foot sole has also previously been shown to evoke reflexes in the lower limb which are topographically organized; these reflex pathways are unknown. The current experiment investigated if a non-noxious electrical stimulus applied to distinct foot sole regions evokes excitatory changes in lower limb muscles via a transcortical pathway. Cortical and spinal excitability were assessed using transcranial magnetic stimulation and cervicomedullary junction stimulation, respectively, following electrical stimulation applied to the heel and metatarsal regions of the foot sole. Comparisons between cortically evoked responses (MEPs) and brainstem evoked responses (CMEPs) during foot sole stimulation represent the neural level of excitability. During foot sole stimulation, the CMEP amplitude increased more than the MEP amplitude. Differences between MEP and CMEP suggest a cortical loop is involved in these cutaneous reflex responses.