Dynamic modulation of intrinsic functional connectivity by transcranial direct current stimulation

Abstract

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique capable of modulating cortical excitability and thereby influencing behavior and learning. Recent evidence suggests that bilateral tDCS over both primary sensorimotor cortices (SM1) yields more prominent effects on motor performance in both healthy subjects and chronic stroke patients than unilateral tDCS over SM1. To better characterize the underlying neural mechanisms of this effect, we aimed to explore changes in resting-state functional connectivity during both stimulation types. In a randomized single-blind crossover design, 12 healthy subjects underwent functional magnetic resonance imaging at rest before, during, and after 20 min of unilateral, bilateral, and sham tDCS stimulation over SM1. Eigenvector centrality mapping (ECM) was used to investigate tDCS-induced changes in functional connectivity patterns across the whole brain. Uni- and bilateral tDCS over SM1 resulted in functional connectivity changes in widespread brain areas compared with sham stimulation both during and after stimulation. Whereas bilateral tDCS predominantly modulated changes in primary and secondary motor as well as prefrontal regions, unilateral tDCS affected prefrontal, parietal, and cerebellar areas. No direct effect was seen under the stimulating electrode in the unilateral condition. The time course of changes in functional connectivity in the respective brain areas was nonlinear and temporally dispersed. These findings provide evidence toward a network-based understanding regarding the underpinnings of specific tDCS interventions.

Baseline effects of transcranial direct current stimulation on glutamatergic neurotransmission and large-scale network connectivity

“…This is an important finding because tDCS-induced increases in inter-hemispheric functional connectivity are thought to be largely dependent on the contributions of the cathode electrode (Sehm et al, 2012; 2013; Park et al, 2013). In the present study, network connectivity was increased predominantly in the left lateral inferior parietal regions of the bilateral inferior parietal and the left frontal-parietal networks.…”

“…Research is underway to examine ways to harness neuroplasticity in order to promote healing and recovery (see Peled, 2004; 2005; Spedding et al, 2003; and Kays et al, 2012 for review). Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that modulates the excitability of functional brain networks (Polania et al, 2011; Keeser et al, 2011; Sehm et al, 2012; Peña-Gómez et al, 2012). It is thought to increase the spontaneous firing of cortical neurons near the anodal electrode (with positive polarity) while decreasing it near the cathode (with negative polarity) (Nitsche and Paulus, 2000; Dieckhöfer et al, 2006).…”

“…Increases in ICA-generated functional connectivity in the cerebellum, medial occipital, sensorimotor, right frontal parietal, and superior frontal gyrus were observed, while decreases were found in the right putamen and lateral occipital areas. Furthermore, active tDCS has also contributed to both inter-hemispheric (Sehm et al, 2012; 2013; Park et al, 2013) and corticostriatal functional connectivity (Polania et al, 2012; Clemens et al, 2014). Overall, studies that combine fMRI and tDCS show widespread changes in functional connectivity at both local and distant brain regions relative to the area of stimulation (Polania et al, 2011; Keeser et al, 201; Amadi et al, 2014).…”

Non-Invasive Brain Stimulation in Dementia: A Complex Network Story

“…Increased functional connectivity (FC) was found both in regions proximal to the electrode [30, 34, 38] and in distal regions belonging to the sensorimotor network [31, 36, 39]. Similarly, studies using graph theory, an approach taking into account network topology and synchronization between brain hubs [64], suggested a network-specific enhancement of connectivity following atDCS [32, 33, 35, 37]. Taken together, these results suggest that atDCS targeting the motor cortex induce increased connectivity, exerting both local and distal effects within the sensorimotor network.…”

Non-invasive brain stimulation in neurorehabilitation: local and distant effects for motor recovery

“…A direct comparison of the effects of bilateral (with the anode over right M1 and cathode over left M1) vs. unilateral tDCS (with the anode over over right M1 and cathode over left supraorbital region) with fMRI was done in healthy volunteers (Sehm et al, 2012). Bilateral tDCS resulted in resting state changes in both primary and secondary motor areas, as well as in the prefrontal cortex, while unilateral M1 stimulation (with the anode over right M1 and cathode over the left supraorbital region) only influenced prefrontal, parietal, and cerebellar areas.…”