Transient Modulation of Working Memory Performance and Event-Related Potentials by Transcranial Static Magnetic Field Stimulation over the Dorsolateral Prefrontal Cortex

Xiaoxiao Chen,Tatsuya Mima,Tatsunori Watanabe,Shota Date,Toru Sunagawa,Takayuki Kuwabara,Keisuke Yunoki,Nami Kubo,Takuya Matsumoto,Hikari Kirimoto

doi:10.3390/brainsci11060739

Abstract

Transcranial static magnetic field stimulation (tSMS) can modulate human cortical excitability and behavior. To better understand the neuromodulatory effect of tSMS, this study investigates whether tSMS applied over the left dorsolateral prefrontal cortex (DLPFC) modulates working memory (WM) performance and its associated event-related potentials (ERPs). Thirteen healthy participants received tSMS or sham stimulation over the left DLPFC for 26 min on different days. The participants performed a 2-back version of the n-back task before, during (20 min after the start of stimulation), immediately after, and 15 min after the stimulation. We examine reaction time for correct responses, d-prime reflecting WM performance, and the N2 and P3 components of ERPs. Our results show that there was no effect of tSMS on reaction time. The d-prime was reduced, and the N2 latency was prolonged immediately after tSMS. These findings indicate that tSMS over the left DLPFC affects WM performance and its associated electrophysiological signals, which can be considered an important step toward a greater understanding of tSMS and its use in studies of higher-order cognitive processes.

Highlights

Non-invasive brain stimulation (NIBS) is an important subject of study in the field of clinical neuroscience, due to its modulatory effects on human brain excitability
As N2 and P3 have been estimated to originate from the anterior cingulate cortex (ACC) and its related networks [37,40], they were observed in all the frontal positions; we focused on the average of F3, Fz, and F4 positions, similar to a previous study [50]
The reason we observed a reduction in working memory (WM) performance only after transcranial static magnetic field stimulation (tSMS) removal and not during the tSMS is hard to interpret; we propose two possibilities: First, since the stimulation duration was longer at the post-0 session than at the during-20 session (20 min), a longer stimulation duration may have been necessary to induce the effect on WM performance

Summary

Introduction

Non-invasive brain stimulation (NIBS) is an important subject of study in the field of clinical neuroscience, due to its modulatory effects on human brain excitability. The effectiveness of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) in the treatment of clinical conditions has been studied extensively over several decades [1,2] In addition to these two techniques, transcranial static magnetic field stimulation (tSMS), which uses a neodymium magnet (NdFeB; diameter, 45 mm; height, 30 mm; maximal strength, 765N) [3], has received much attention recently as a less costly and potentially safer alternative. Several studies report non-significant effects by tSMS [4,5,6], an accumulating body of evidence suggests that tSMS is a powerful NIBS technique that can modulate human functions [7]. To our best knowledge, at present, there exists no study investigating the effect of tSMS on working memory (WM) performance

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