RESTING STATE FMRI: A TOOL TO INVESTIGATE FUNCTIONAL CONNECTIVITY MODULATION INDUCED BY TRANSCRANIAL DIRECT CURRENT STIMULATION OF THE MOTOR NETWORK

Abstract

Introduction: Resting-state functional connectivity (fcMRI) represents a novel fMRI approach that allows detection of temporal correlations in spontaneous BOLD signal oscillations while subjects rest quietly in the scanner. Under resting conditions the brain is engaged in spontaneous activity that causes a low frequencies (<0.1 Hz) BOLD signal fluctuations. Functional connectivity (FC) can be defined as the synchrony of neural activity among spatially distant regions. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that is known to modulate cortical activity and FC among brain regions, as measured by functional magnetic resonance imaging. This study is aimed at measuring the variation of functional connectivity between cortical brain regions after tDCS along time. Materials and Methods: For this purpose we enrolled 20 healthy righthanded subjects. All subjects underwent 4 sessions RS-fMRI (10’ each, TR 2’’, 300 volumes, 1.5 T scanner): 2 immediately before and 2 after 20’ tDCS over leftM1. 10 of them received real (anodal) tDCS, 10 received sham stimulation. We analyzed FC between left and right M1 with two different statistical analyses: Seed-based correlation analysis (SCA) and the temporal concatenation group ICA (TC-GICA). Results: Seed-based correlation analysis showed a significant decrease of FC during the first fMRI acquisition immediately after anodal tDCS stimulation (p = 0.005) that reaches back to baseline during the last fMRI session. This behavior was not found in subjects who underwent sham stimulation (p = 0.12). The temporal concatenation group ICA showed that immediately after anodal stimulation the average value of voxels decreases significantly (p < 0.05) whereas there is no significant decrease in the case of sham tDCS stimulation. Conclusions: Our results show that anodal tDCS is able to induce connectivity changes within motor network, that is, reversible in a period lasting between 10’ and 20’ after stimulation.