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

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.

Non-Invasive Brain Stimulation Improves Paretic Limb Force Production: A Systematic Review and Meta-Analysis

“…tDCS and rTMS administered on M1 are known to facilitate local changes in M1 as well as distant changes in interconnected brain regions (i.e., premotor cortex and supplementary motor area) [22]. Given that an increased interconnectivity between M1 and other brain regions improved paretic limb functions [74], one promising stroke motor rehabilitation approach would be investigating the effects of anodal tDCS or high frequency rTMS stimulation on multiple motor areas (i.e., M1, premotor cortex, and supplementary motor area) within the ipsilesional hemisphere.…”

Imaging human brain networks to improve the clinical efficacy of non-invasive brain stimulation

“…Several studies have also investigated the effect of tDCS on whole-brain network activity (Polania et al, 2011;Pena-Gomez et al, 2012;Sehm et al, 2013). These studies have A c c e p t e d M a n u s c r i p t Sale et al,19 shown that tDCS has profound yet predictable effects on widespread functional connectivity.…”

“…It appears the position of the stimulating pads is important in mediating the network effects of tDCS. When the primary sensorimotor cortex (SM1) was stimulated with tDCS, the position of the return electrode had a significant impact on patterns of functional connectivity (Sehm et al, 2013). With the return electrode located over the homologous SM1 region of the contralateral cortex, the induced neural changes were restricted to primary and secondary motor areas (i.e., within the sensorimotor network; e.g., Fig.…”

“…Studies suggest that the global effect induced by NIBS is dependent on several factors including electrode placement (Sehm et al, 2013), connectedness of the targeted brain region to other regions (e.g., Rounis et al, 2006vs. Cocchi et al, 2015, and whether the participant is concurrently undertaking a task (Nitsche et al, 2003;Fregni et al, 2005;Hummel et al, 2005;Kujirai et al, 2006;Andrews et al, 2011).…”

Does transcranial direct current stimulation enhance cognitive and motor functions in the ageing brain? A systematic review and meta- analysis

“…Furthermore, this research has largely focussed on local changes underneath an electrode, but there is clear evidence from neuroimaging studies that standard tDCS protocols produce widespread changes in cortical activity across a number of connected brain regions (Zheng et al, 2011). These studies have shown that tDCS can modulate both inter-hemispheric and corticospinal functional connectivity (Polania et al, 2012;Sehm et al, 2013). Age-related differences in connectivity patterns that relate to memory performance have also been reported (Sala-Llonch et al, 2014).…”