Date of Degree
Synchronized arrival of neuronal signals from the periphery and motor cortex has been associated with neuronal plasticity and motor learning. The main objective of this study was to examine neuronal interactions following excitation of descending motor axons from the primary motor cortex (M1) and spinal neuronal circuits via transcranial magnetic stimulation (TMS) and transcutaneous electric stimulation of the spine (tsESS) in 15 healthy humans while seated semiprone. TMS was delivered below or above the resting motor evoked potential (MEP) threshold, for the tibialis anterior (TA) muscle, while tsESS was delivered at the lowest stimulation intensity that evoked responses in most or all leg muscles. TMS was delivered either alone or with tsESS at different interstimulus intervals ranging from negative 50 ms to positive 50 ms. tsESS induced a biphasic excitability pattern of MEPs recorded from the distal ankle muscles of the right leg with negative interstimulus intervals showing depression of MEPs followed by a non significant effect at the interstimulus interval of 0 ms, and potentiation of MEPs at positive interstimulus intervals. These findings suggest that 1) cortical descending motor volleys can either be potentiated or depressed based on the time that cortical and spinal signals meet at the spinal cord level, and 2) MEPs and tsESS-induced compound action muscle potentials likely share common neuronal pathways. These findings constitute the first evidence that synchronized neuronal signals from the primary motor cortex and spine can potentiate corticospinal motor output.
Asmar, Amanda; Manfredini, Leandra; McLean, Kerri; and Scannapieco, Christina, "Corticospinal Integration in Healthy Humans" (2014). CUNY Academic Works.