Theta‐burst repetitive transcranial magnetic stimulation suppresses specific excitatory circuits in the human motor cortex

TLDR

Low‑frequency rTMS has been shown to suppress motor‑evoked potentials elicited by single‑pulse TMS. This study aimed to determine the CNS level at which 1‑Hz rTMS reduces MEP amplitude. Corticospinal volleys were recorded before and after 1‑Hz rTMS in five subjects with cervical epidural electrodes, including one Parkinson’s patient on medication. 1‑Hz rTMS significantly reduced the amplitude of later I‑waves and associated MEPs while sparing the earliest I‑wave, indicating a cortical origin of the suppression.

Abstract

Previous studies have shown that low-frequency repetitive transcranial magnetic stimulation (rTMS) suppresses motor-evoked potentials (MEPs) evoked by single pulse TMS. The aim of the present paper was to investigate the central nervous system level at which rTMS produces a suppression of MEP amplitude. We recorded corticospinal volleys evoked by single pulse TMS of the motor cortex before and after 1 Hz rTMS in five conscious subjects who had an electrode implanted in the cervical epidural space for the control of pain. One of the patients had Parkinson's disease and was studied on medication. Repetitive TMS significantly suppressed the amplitude of later I-waves, and reduced the amplitude of concomitantly recorded MEPs. The earliest I-wave was not significantly modified by rTMS. The present results show that 1 Hz rTMS may decrease the amplitude of later descending waves, consistent with a cortical origin of the effect of 1 Hz rTMS on MEPs.