Multipulse transcranial magnetic stimulation of human motor cortex produces short-latency corticomotor facilitation via two distinct mechanisms

Abstract

TMS pairs evoke SICF at interpulse intervals (IPIs) that match I-wave periodicity. Biphasic bursts with IPIs at the latency of the first peak facilitate MEPs and reduce corticomotor threshold. Bursts at the latency of the first trough facilitate MEPs and reduce corticomotor threshold to a lesser extent. TMS bursts facilitate corticomotor excitability via two mechanisms: SICF-dependently via fast-conducting direct projections from M1HAND to spinal motoneurons and SICF-independently, probably through slower-conducting indirect pyramidal tract projections.