30 Hz Theta-burst Stimulation Over Primary Somatosensory Cortex Modulates Corticospinal Output to the Hand

BACKGROUND: The primary somatosensory cortex (SI) is important for hand function and has direct connectivity with the primary motor cortex (M1). Much of our present knowledge of this connectivity and its relevance to hand function is based on animal research. In humans, less is known about the neural mechanisms by which SI influences motor circuitry that outputs to the muscles controlling the hand. OBJECTIVE: The present study investigated the influence of SI on corticospinal excitability, and inhibitory and excitatory intracortical neural circuitry within M1 before and after continuous theta-burst stimulation (cTBS). Motor-evoked potentials (MEPs), short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF) were recorded from the first dorsal interosseous (RFDI) muscle of the right hand following 30 Hz cTBS over left-hemisphere SI and M1 delivered in separate sessions. RESULTS: cTBS over SI facilitated MEPs and did not alter ICF or SICI. cTBS delivered over M1 suppressed MEPs and ICF and did not alter SICI. CONCLUSIONS: These findings indicate that SI influences corticospinal output to the hand, possibly via corticocortical projections, and may be one mechanism by which somatosensory information influences hand control.