Mapping of the supplementary motor area using repetitive navigated transcranial magnetic stimulation

Giulia Kern; Miriam Kempter; Thomas Picht; Melina Engelhardt

doi:10.3389/fnins.2023.1255209

Mapping of the supplementary motor area using repetitive navigated transcranial magnetic stimulation

Front Neurosci. 2023 Oct 4:17:1255209. doi: 10.3389/fnins.2023.1255209. eCollection 2023.

Authors

Giulia Kern¹, Miriam Kempter¹, Thomas Picht^{1

2

3}, Melina Engelhardt^{1

2

4}

Affiliations

¹ Department of Neurosurgery, Charité - Universitätsmedizin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany.
² Einstein Center for Neurosciences, Charité - Universitätsmedizin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany.
³ Cluster of Excellence Matters of Activity, Image Space Material, Humboldt-Universität zu Berlin, Berlin, Germany.
⁴ International Graduate Program Medical Neurosciences, Charité - Universitätsmedizin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany.

Abstract

Background: The supplementary motor area (SMA) is important for motor and language function. Damage to the SMA may harm these functions, yet tools for a preoperative assessment of the area are still sparse.

Objective: The aim of this study was to validate a mapping protocol using repetitive navigated transcranial magnetic stimulation (rnTMS) and extend this protocol for both hemispheres and lower extremities.

Methods: To this purpose, the SMA of both hemispheres were mapped based on a finger tapping task for 30 healthy subjects (35.97 ± 15.11, range 21-67 years; 14 females) using rnTMS at 20 Hz (120% resting motor threshold (RMT)) while controlling for primary motor cortex activation. Points with induced errors were marked on the corresponding MRI. Next, on the identified SMA hotspot a bimanual finger tapping task and the Nine-Hole Peg Test (NHPT) were performed. Further, the lower extremity was mapped at 20 Hz (140%RMT) using a toe tapping task.

Results: Mean finger tapping scores decreased significantly during stimulation (25.70taps) compared to baseline (30.48; p < 0.01). Bimanual finger tapping led to a significant increase in taps during stimulation (28.43taps) compared to unimanual tapping (p < 0.01). Compared to baseline, completion time for the NHPT increased significantly during stimulation (baseline: 13.6 s, stimulation: 16.4 s; p < 0.01). No differences between hemispheres were observed.

Conclusion: The current study validated and extended a rnTMS based protocol for the mapping of the SMA regarding motor function of upper and lower extremity. This protocol could be beneficial to better understand functional SMA organisation and improve preoperative planning in patients with SMA lesions.

Keywords: TMS; brain mapping; motor function; preoperative diagnostic; supplementary motor area.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The authors acknowledge the support of the Cluster of Excellence Matters of Activity. Image Space Material funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC 2025-390648296. We acknowledge financial support from the Open Access Publication Fund of Charité – Universitätsmedizin Berlin and the German Research Foundation (DFG).