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ORIGINAL RESEARCH article

Front. Neurol.

Sec. Experimental Therapeutics

Volume 16 - 2025 | doi: 10.3389/fneur.2025.1628204

This article is part of the Research TopicNon-Invasive Brain Stimulation: From Basic Science to Clinical ApplicationView all articles

Connectivity between supplementary motor complex and primary motor cortex: a dual-coil paired-pulse TMS study

Provisionally accepted
Hakjoo KimHakjoo Kim1,2,3Yuming LeiYuming Lei3Shancheng BaoShancheng Bao3Angelina T HuynhAngelina T Huynh3John J BuchananJohn J Buchanan3Jessica A BernardJessica A Bernard4Joshua C BrownJoshua C Brown1,2David L WrightDavid L Wright3*
  • 1Department of Psychiatry, Harvard Medical School, Boston, United States
  • 2Division of Depression and Anxiety Disorders, McLean Hospital, Belmont, United States
  • 3Division of Kinesiology, Texas A&M University, College Station, United States
  • 4Department of Psychological and Brain Sciences, Texas A&M University, College Station, United States

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Dual-coil paired-pulse transcranial magnetic stimulation (ppTMS) has garnered interest for its potential in elucidating neural circuit dynamics. In this study, the dual-coil ppTMS was utilized to assess the effective connectivity between the supplementary motor complex (SMC) and the primary motor cortex (M1) in humans. A robust facilitatory connection between the SMC and M1 was observed, manifested as a 19% increase in mean peak-to-peak motor-evoked potentials following conditioning of SMC 7 ms prior to M1 stimulation. Importantly, the facilitatory influence of SMC was found in subjects who received conditioning stimulation 4 cm anterior to Cz, but not in those stimulated at 5 cm, 6 cm, or 7 cm. While previous work has focused on demonstrating important temporal dynamics for SMC-M1 plasticity, the present findings highlight a critical contribution of spatial specificity for the modulation of SMC-M1 circuitry.

Keywords: Transcranial Magnetic Stimulation, paired-pulse transcranial magnetic stimulation (ppTMS), supplementary motor complex (SMC), pre-supplementary motor area (pre-SMA), Supplementary motor area (SMA), SMC-M1 Circuitry, SMA-M1 paired stimulation, plasticity

Received: 20 May 2025; Accepted: 15 Sep 2025.

Copyright: © 2025 Kim, Lei, Bao, Huynh, Buchanan, Bernard, Brown and Wright. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: David L Wright, davidwright@tamu.edu

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

Supplementary Material