Alterations to GABAergic Inhibition In Primary Motor Cortex

Abstract

Motor evoked potential (MEP) and short- and long-interval intracortical inhibition (SICI and LICI) are measures for corticospinal output and intracortical inhibition within the primary motor cortex (M1), respectively. These measures are known to be associated with motor output and control and have been implicated within neurophysiological disorders. It is likely that the dysfunction of such motor cortical circuits are associated with the motor deficiencies presented within clinical populations such as spinal cord injury (SCI), amyloid lateral sclerosis, and focal hand dystonia. In Experiment 1, the MEP, SICI, and LICI circuits were characterized in participants with incomplete SCI and compared to uninjured controls to identify differences. MEPs and SICI were reduced while LICI was increased in participants with SCI. In Experiment 2, single and paired continuous theta burst stimulation (cTBS) were delivered over M1 or primary somatosensory cortex (SI) in order to induce plasticity within either cortical areas and produce changes to MEP and SICI. All interventions were able to facilitate MEP, but none of the interventions were sufficient in altering SICI. The findings in this thesis highlight the alterations in motor cortical circuits associated with motor output and control within the SCI population and the potential interventions that can be implemented in reverting those circuit changes.