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Anodal tDCS over the supplementary motor area increases motor overflow during imagined aiming movement

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Abstract

Neural networks subserving motor imagery and action observation overlap with those involved in motor execution. The precise roles of specific cortical areas in these processes are not fully understood. One cortical area implicated in motor imagery is the supplementary motor area (SMA). To test the role of SMA in motor imagery, participants without any known neurological disorders (N = 23) completed three versions of a reciprocal manual aiming task (imagined, observed, and executed movements) before and after transcranial direct current stimulation (tDCS) was applied to the SMA. Anodal, cathodal, and sham (inactive) stimulation protocols were compared within participants. Although the speed-accuracy trade-off observed in the aiming task was not affected by tDCS, the amount of incidental movement during imagery (motor overflow) increased following anodal stimulation. Additionally, imagined movement time was associated less strongly with an implicit measure of motor imagery (hand laterality judgement) following anodal tDCS compared to the sham condition. No effects of tDCS were found for action observation or movement execution. These results suggest that anodal stimulation applied over SMA may subtly disrupt processes underlying motor imagery, either through unintended inhibitory effects or via excitatory effects on adjacent areas of the motor cortex.

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Data will be made available on reasonable request to the authors.

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Acknowledgements

The authors thank Maryam Hassanzahraee, Joyce Chen, and Bisman Mangat for feedback on study design and interpretation, and Sydney Winokur and Zheng Tan for assistance with data processing and modelling.

Funding

This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). J. Bek was also supported by funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 101034345.

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Authors and Affiliations

  1. Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Canada

    Judith Bek, Xiaoye Michael Wang & Timothy N. Welsh

  2. School of Psychology, University College Dublin, Dublin, Ireland

    Judith Bek

Authors
  1. Judith Bek
  2. Xiaoye Michael Wang
  3. Timothy N. Welsh

Contributions

JB: Conceived and designed research, performed experiments, analyzed data, interpreted results of experiments, prepared figures, drafted manuscript, edited and revised manuscript, approved final version of manuscript. XW: Analyzed data, interpreted results of experiments, edited and revised manuscript, approved final version of manuscript. TW: Conceived and designed research, interpreted results of experiments, edited and revised manuscript, approved final version of manuscript.

Corresponding author

Correspondence to Judith Bek.

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The authors declare that they have no conflict of interest.

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Bek, J., Wang, X.M. & Welsh, T.N. Anodal tDCS over the supplementary motor area increases motor overflow during imagined aiming movement. Exp Brain Res 243, 248 (2025). https://doi.org/10.1007/s00221-025-07196-4

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  • DOI: https://doi.org/10.1007/s00221-025-07196-4

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