Contrasting MEG effects of anodal and cathodal high-definition TDCS on sensorimotor activity during voluntary finger movements

Jed A Meltzer; Gayatri Sivaratnam; Tiffany Deschamps; Maryam Zadeh; Catherine Li; Faranak Farzan; Alex Francois-Nienaber

doi:10.3389/fnimg.2024.1341732

Contrasting MEG effects of anodal and cathodal high-definition TDCS on sensorimotor activity during voluntary finger movements

Front Neuroimaging. 2024 Feb 5:3:1341732. doi: 10.3389/fnimg.2024.1341732. eCollection 2024.

Authors

Jed A Meltzer^{1

2}, Gayatri Sivaratnam¹, Tiffany Deschamps¹, Maryam Zadeh¹, Catherine Li¹, Faranak Farzan³, Alex Francois-Nienaber¹

Affiliations

¹ Rotman Research Institute, Baycrest Academy for Research and Education, Toronto, ON, Canada.
² Departments of Psychology and Speech-language Pathology, University of Toronto, Toronto, ON, Canada.
³ School of Mechatronic Systems Engineering, Simon Fraser University, Burnaby, BC, Canada.

Abstract

Introduction: Protocols for noninvasive brain stimulation (NIBS) are generally categorized as "excitatory" or "inhibitory" based on their ability to produce short-term modulation of motor-evoked potentials (MEPs) in peripheral muscles, when applied to motor cortex. Anodal and cathodal stimulation are widely considered excitatory and inhibitory, respectively, on this basis. However, it is poorly understood whether such polarity-dependent changes apply for neural signals generated during task performance, at rest, or in response to sensory stimulation.

Methods: To characterize such changes, we measured spontaneous and movement-related neural activity with magnetoencephalography (MEG) before and after high-definition transcranial direct-current stimulation (HD-TDCS) of the left motor cortex (M1), while participants performed simple finger movements with the left and right hands.

Results: Anodal HD-TDCS (excitatory) decreased the movement-related cortical fields (MRCF) localized to left M1 during contralateral right finger movements while cathodal HD-TDCS (inhibitory), increased them. In contrast, oscillatory signatures of voluntary motor output were not differentially affected by the two stimulation protocols, and tended to decrease in magnitude over the course of the experiment regardless. Spontaneous resting state oscillations were not affected either.

Discussion: MRCFs are thought to reflect reafferent proprioceptive input to motor cortex following movements. Thus, these results suggest that processing of incoming sensory information may be affected by TDCS in a polarity-dependent manner that is opposite that seen for MEPs-increases in cortical excitability as defined by MEPs may correspond to reduced responses to afferent input, and vice-versa.

Keywords: MCRF; TDCS; beta oscillations; gamma oscillations; magnetoencephalography (MEG); motor cortex; polarity.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. Funding was provided by a Basic Science Grant from the Ontario Brain Institute, the Canada Research Chairs program (231634), and a Discovery Grant (RGPIN-2019-06515) from the Natural Sciences and Engineering Research Council of Canada.