Influence of Concurrent Finger Movements on Transcranial Direct Current Stimulation (tDCS)-Induced Aftereffects.

Yuichiro Shirota,Walter Paulus,Daniella Terney,Andrea Antal

doi:10.3389/fnbeh.2017.00169

Abstract

Transcranial direct current stimulation (tDCS) has been reported to have bidirectional influence on the amplitude of motor-evoked potentials (MEPs) in resting participants in a polarity-specific manner: anodal tDCS increased and cathodal tDCS decreased them. More recently, the effects of tDCS have been shown to depend on a number of additional factors. We investigated whether a small variety of movements involving target and non-target muscles could differentially modify the efficacy of tDCS. MEPs were elicited from the right first dorsal interosseous muscle, defined as the target muscle, by single pulse transcranial magnetic stimulation (TMS) over the primary motor cortex (M1). During M1 tDCS, which lasted for 10 min applying anodal, cathodal, or sham condition, the participants were instructed to squeeze a ball with their right hand (Task 1), to move their right index finger only in the medial (Task 2), in the lateral direction (Task 3), or in medial and lateral direction alternatively (Task 4). Anodal tDCS reduced MEP amplitudes measured in Task 1 and Task 2, but to a lesser extent in the latter. In Task 3, anodal tDCS led to greater MEP amplitudes than cathodal stimulation. Alternating movements resulted in no effect of tDCS on MEP amplitude (Task 4). The results are congruent with the current notion that the aftereffects of tDCS are highly variable relying on a number of factors including the type of movements executed during stimulation.

Highlights

Transcranial direct current stimulation was originally introduced as a powerful tool to modulate cortical excitability bidirectionally, depending on the polarity with which it was applied
RMT, AMT, SI1mV, and baseline motor evoked potential (MEP) amplitudes were compared between anodal, cathodal and sham conditions within each task
In this study we found that different hand and finger movements during Transcranial direct current stimulation (tDCS) resulted in different modulations of mean MEP amplitudes, indicating that the brain status during tDCS is one of the key factors in determining its effect

Summary

Introduction

Transcranial direct current stimulation (tDCS) was originally introduced as a powerful tool to modulate cortical excitability bidirectionally, depending on the polarity with which it was applied. The first studies reported that anodal tDCS increased the amplitude of the motor evoked potentials (MEPs), probably by increasing the excitability of the primary motor cortex (M1) (Nitsche and Paulus, 2000, 2001) while cathodal tDCS diminished it (Nitsche and Paulus, 2000; Nitsche et al, 2003). Pharmacological evidence suggested that altered membrane potential and synaptic plasticity contributed to the polarityspecific aftereffects of tDCS (Liebetanz et al, 2002; Nitsche et al, 2003a). The positive influence of tDCS on learning (Nitsche et al, 2003b; Galea and Celnik, 2009; Reis et al, 2009) promoted its therapeutic applications, including those for stroke rehabilitation (Kang et al, 2016; Meinzer et al, 2016).

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