A Comparison between Uni- and Bilateral tDCS Effects on Functional Connectivity of the Human Motor Cortex

Bernhard Sehm,Patrick Ragert,Alexander Schäfer,Arno Villringer,Judy Kipping

doi:10.3389/fnhum.2013.00183

Abstract

Transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) has been shown to induce changes in motor performance and learning. Recent studies indicate that tDCS is capable of modulating widespread neural network properties within the brain. However the temporal evolution of online- and after-effects of tDCS on functional connectivity (FC) within and across the stimulated motor cortices (M1) still remain elusive. In the present study, two different tDCS setups were investigated: (i) unilateral M1 tDCS (anode over right M1, cathode over the contralateral supraorbital region) and (ii) bilateral M1 tDCS (anode over right M1, cathode over left M1). In a randomized single-blinded cross-over design, 12 healthy subjects underwent functional magnetic resonance imaging at rest before, during and after 20 min of either bi-, unilateral, or sham M1 tDCS. Seed-based FC analysis was used to investigate tDCS-induced changes across and within M1. We found that bilateral M1 tDCS induced (a) a decrease in interhemispheric FC during stimulation and (b) an increase in intracortical FC within right M1 after termination of the intervention. While unilateral M1 tDCS also resulted in similar effects during stimulation, no such changes could be observed after termination of tDCS. Our results provide evidence that depending on the electrode montage, tDCS acts upon a modulation of either intracortical and/or interhemispheric processing of M1.

Highlights

Over the past decades, non-invasive brain stimulation techniques have been used to investigate mechanisms of motor control and motor learning
We found that bilateral M1 Transcranial direct current stimulation (tDCS) induced (a) a decrease in interhemispheric functional connectivity (FC) during stimulation and (b) an increase in intracortical FC within right M1 after termination of the intervention
TDCS-INDUCED FUNCTIONAL CONNECTIVITY CHANGES OF THE MOTOR CORTEX (RIGHT M1 SEED) Bilateral M1 tDCS Bilateral M1 tDCS as compared to sham resulted in a decrease in interhemispheric FC (IHFC) between right and left M1 during the last block of stimulation

Summary

Introduction

Non-invasive brain stimulation techniques have been used to investigate mechanisms of motor control and motor learning. In line with the capability of modulating excitability, anodal tDCS applied over M1 is capable of facilitating motor behavior and learning of the contralateral hand (Nitsche et al, 2003b; Reis et al, 2009). In addition to excitatory anodal stimulation of M1 contralateral to a hand exerting a motor task, the inhibitory cathode is placed over ipsilateral M1. Two studies directly compared the effects of both approaches in healthy subjects on performance or learning of unilateral sequential finger movements and yielded somewhat diverging results: while one study found an improvement in task performance only during bilateral M1 tDCS (Vines et al, 2008) another study did not find differences in implicit motor learning during bilateral as compared to unilateral M1 tDCS (Kang and Paik, 2011)

Methods

Results

Discussion

Conclusion