Static magnetic stimulation of the primary motor cortex impairs online but not offline motor sequence learning

Angélina Lacroix,Raphaël Hamel,Léa Proulx-Bégin,Jean-François Lepage,Louis De Beaumont,Pierre-Michel Bernier

doi:10.1038/s41598-019-46379-2

Angélina Lacroix, Raphaël Hamel + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-46379-2

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Journal: Scientific Reports	Publication Date: Jul 8, 2019
Citations: 13	License type: open-access

Affiliation: Université de Sherbrooke

Abstract

Static magnetic fields (SMFs) are known to alter neural activity, but evidence of their ability to modify learning-related neuroplasticity is lacking. The present study tested the hypothesis that application of static magnetic stimulation (SMS), an SMF applied transcranially via a neodymium magnet, over the primary motor cortex (M1) would alter learning of a serial reaction time task (SRTT). Thirty-nine participants took part in two experimental sessions separated by 24 h where they had to learn the SRTT with their right hand. During the first session, two groups received SMS either over contralateral (i.e., left) or ipsilateral (i.e., right) M1 while a third group received sham stimulation. SMS was not applied during the second session. Results of the first session showed that application of SMS over contralateral M1 impaired online learning as compared to both ipsilateral and sham groups, which did not differ. Results further revealed that application of SMS did not impair offline learning or relearning. Overall, these results are in line with those obtained using other neuromodulatory techniques believed to reduce cortical excitability in the context of motor learning and suggest that the ability of SMS to alter learning-related neuroplasticity is temporally circumscribed to the duration of its application.

Highlights

Exposure to strong static magnetic fields (SMFs) is known to bear an influence on biological systems[1,2]
Initial studies suggested that the effects of static magnetic stimulation (SMS) on the brain were relatively short-lived (i.e., ~10 minutes)[3,6,16], but recent transcranial magnetic stimulation (TMS) evidence shows that a 30-minute exposure to SMS over the primary motor cortex (M1) could induce enduring neurophysiological changes consistent with long-term depression (LTD)-like effects[8]
Low-frequency repetitive TMS and continuous theta-burst TMS applied to the contralateral M1, which are believed to induce LTD-like plasticity, appear to interfere with the consolidation processes involved in offline learning of SRTT29–31

Summary

Introduction

Exposure to strong static magnetic fields (SMFs) is known to bear an influence on biological systems[1,2]. Initial studies suggested that the effects of SMS on the brain were relatively short-lived (i.e., ~10 minutes)[3,6,16], but recent transcranial magnetic stimulation (TMS) evidence shows that a 30-minute exposure to SMS over the primary motor cortex (M1) could induce enduring neurophysiological changes consistent with long-term depression (LTD)-like effects[8]. Whether these lasting LTD-like changes are strong enough to modify behaviour after the stimulation period (i.e. offline effects), or whether the behavioural effects of SMS are temporally circumscribed to the duration of its application, remains to be clarified. In the eventuality that SMS induced lasting LTD-like effects[8], we would expect contralateral SMS to decrease offline learning as compared to the other stimulation conditions

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