Modulation of large-scale brain networks by transcranial direct current stimulation evidenced by resting-state functional MRI

Abstract

Background Brain areas interact mutually to perform particular complex brain functions such as memory or language. Furthermore, under resting-state conditions several spatial patterns have been identified that resemble functional systems involved in cognitive functions. Among these, the default-mode network (DMN), which is consistently deactivated during task periods and is related to a variety of cognitive functions, has attracted most attention. In addition, in resting-state conditions some brain areas engaged in focused attention (such as the anticorrelated network, AN) show a strong negative correlation with DMN; as task demand increases, AN activity rises, and DMN activity falls. Objective We combined transcranial direct current stimulation (tDCS) with functional magnetic resonance imaging (fMRI) to investigate these brain network dynamics. Methods Ten healthy young volunteers underwent four blocks of resting-state fMRI (10-minutes), each of them immediately after 20 minutes of sham or active tDCS (2 mA), on two different days. On the first day the anodal electrode was placed over the left dorsolateral prefrontal cortex (DLPFC) (part of the AN) with the cathode over the contralateral supraorbital area, and on the second day, the electrode arrangement was reversed (anode right-DLPFC, cathode left-supraorbital). Results After active stimulation, functional network connectivity revealed increased synchrony within the AN components and reduced synchrony in the DMN components. Conclusions Our study reveals a reconfiguration of intrinsic brain activity networks after active tDCS. These effects may help to explain earlier reports of improvements in cognitive functions after anodal-tDCS, where increasing cortical excitability may have facilitated reconfiguration of functional brain networks to address upcoming cognitive demands.

Excitability modulation of the motor system induced by transcranial direct current stimulation: A multimodal approach

“…This result is consistent with a recent study (Zheng et al, 2011) that reports a positive correlation between the stimulated motor cortex and the contralateral one, supporting a possible coupling of neuroactivity between motor regions (although in our study, the stimulated hemisphere was more strongly activated than the contralateral region). We suppose that the mechanisms responsible for this widespread and bihemispheric anodal effect Pena-Gomez et al, 2011;Polania et al, 2010b) could involve current flowing in subcortical regions such as the thalamus (Bindman et al, 1962), which is the principal subcortical mediator of the TMS-contralateral response (Komssi et al, 2002). A tDCS-induced effect on the cortico-subcortical networks is supported also by recent evidence of a functional coupling increase on the thalamo-cortical circuits following anodal stimulation over the motor cortex (Polania et al, 2012).…”

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

“…Of particular interest will be how tDCS-induced changes in localised connectivity patterns affect large-scale brain dynamics. For example, Sstimulating the motor cortex has been shown to increase functional connectivity within that structure (Polania et al, 2012), and increased connectivity within the default mode network and attention network has been reported from stimulation of the DLPFC (Keeser et al, 2011;Pena-Gomez et al, 2012). The application of graph theory to network organisation has also identified the presence of hubs that have a large number of connections and appear essential for brain communication.…”

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.…”