The Effects of Transcranial Electrical Stimulation on Human Motor Functions: A Comprehensive Review of Functional Neuroimaging Studies.

Yuanyuan Gao,Suvranu De,Lora Cavuoto,Jack E Norfleet,Xavier Intes,Steven Schwaitzberg

doi:10.3389/fnins.2020.00744

Abstract

Transcranial electrical stimulation (tES) is a promising tool to enhance human motor skills. However, the underlying physiological mechanisms are not fully understood. On the other hand, neuroimaging modalities provide powerful tools to map some of the neurophysiological biomarkers associated with tES. Here, a comprehensive review was undertaken to summarize the neuroimaging evidence of how tES affects human motor skills. A literature search has been done on the PubMed database, and 46 relative articles were selected. After reviewing these articles, we conclude that neuroimaging techniques are feasible to be coupled with tES and offer valuable information of cortical excitability, connectivity, and oscillations regarding the effects of tES on human motor behavior. The biomarkers derived from neuroimaging could also indicate the motor performance under tES conditions. This approach could advance the understanding of tES effects on motor skill and shed light on a new generation of adaptive stimulation models.

Highlights

Electric brain stimulation has been reported as early as the mid-1800s, and since, its utility for clinical applications, including electroconvulsive therapy (Rudorfer et al, 2003), electroanesthesia (Kuzin et al, 1965; Brown, 1975), electrosleep (Feighner et al, 1973), and intraoperative neuromonitoring (Szelényi et al, 2007), has been extensively explored
Before we reviewed the effects of transcranial electric stimulation (tES) on motor functions with neuroimaging evidences, we summarized its effects under resting state as the intrinsic effects
We further reviewed the neuroimaging studies related to motor performance

Summary

INTRODUCTION

Electric brain stimulation has been reported as early as the mid-1800s (von Helmholtz, 1925), and since, its utility for clinical applications, including electroconvulsive therapy (Rudorfer et al, 2003), electroanesthesia (Kuzin et al, 1965; Brown, 1975), electrosleep (Feighner et al, 1973), and intraoperative neuromonitoring (Szelényi et al, 2007), has been extensively explored. Based on this finding from animal models, Nitsche and Paulus (2000) tested transcranial direct current stimulation (tDCS) on humans They found that anodal stimulation could increase, whereas cathodal could decrease, motor cortical excitability. Both cortical activation and connectivity were enhanced by tES under resting state Based on this understanding, we further reviewed the neuroimaging studies related to motor performance . The keywords used during the search included the following: “transcranial electrical stimulation (tES)” OR “transcranial direct current stimulation (tDCS)” OR “transcranial alternating current stimulation (tACS)” OR “transcranial random noise stimulation (tRNS)” AND “neuroimaging” OR “functional magnetic resonance imaging (fMRI)” OR “positron-emission tomography (PET)” OR “electroencephalogram (EEG)” OR “Magnetoencephalography (MEG)” OR “functional near-infrared spectroscopy (fNIRS)” AND “motor.” The articles were filtered by article types: “Clinical trial” OR “Journal article,” species: “Human study” and languages: “English,” resulting in 163 articles. Connectivity Functional connectivity could be derived from the fMRI technique by defining regional cross-correlations of the time iM1-cSO iM1-shoulder iM1-cM1 cSO-iM1 iSO-cM1 cM1-iM1 Cz-FCz I (mA) J (mA/cm2) t (min) f (Hz) Days SMA M1 PFC Pre-motor S1 Insula, frontoparietal

Reduced coherence from

Significantly modulated

Findings

Summary of the Review

CONCLUSION