Assessing cortical synchronization during transcranial direct current stimulation: A graph-theoretical analysis

• Published in: NeuroImage (Orlando, Fla.) Vol. 140; pp. 57 - 65
• Main Authors: Mancini, Matteo, Brignani, Debora, Conforto, Silvia, Mauri, Piercarlo, Miniussi, Carlo, Pellicciari, Maria Concetta
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.10.2016; Elsevier Limited
• Subjects: Adult; Algorithms; Brain; Brain Mapping - methods; Cerebral Cortex - physiology; Computer Simulation; Cortical activity; Cortical Excitability - physiology; Cortical Synchronization - physiology; EEG; Experiments; Female; Functional connectivity; Graph theory; Humans; Male; Models, Neurological; Nerve Net - physiology; Reproducibility of Results; Sensitivity and Specificity; Studies; Synchronization likelihood; tDCS; Time series; Transcranial Direct Current Stimulation - methods; Functional connectivity; tDCS; EEG; ICA; SL; Synchronization likelihood; Cortical activity; Graph theory
• ISSN: 1053-8119; 1095-9572; 1095-9572
• DOI: 10.1016/j.neuroimage.2016.06.003

Transcranial direct current stimulation (tDCS) is a neuromodulation technique that can alter cortical excitability and modulate behaviour in a polarity-dependent way. Despite the widespread use of this method in the neuroscience field, its effects on ongoing local or global (network level) neuronal activity are still not foreseeable. A way to shed light on the neuronal mechanisms underlying the cortical connectivity changes induced by tDCS is provided by the combination of tDCS with electroencephalography (EEG). In this study, twelve healthy subjects underwent online tDCS-EEG recording (i.e., simultaneous), during resting-state, using 19 EEG channels. The protocol involved anodal, cathodal and sham stimulation conditions, with the active and the reference electrodes in the left frontocentral area (FC3) and on the forehead over the right eyebrow, respectively. The data were processed using a network model, based on graph theory and the synchronization likelihood. The resulting graphs were analysed for four frequency bands (theta, alpha, beta and gamma) to evaluate the presence of tDCS-induced differences in synchronization patterns and graph theory measures. The resting state network connectivity resulted altered during tDCS, in a polarity-specific manner for theta and alpha bands. Anodal tDCS weakened synchronization with respect to the baseline over the fronto-central areas in the left hemisphere, for theta band (p<0.05). In contrast, during cathodal tDCS a significant increase in inter-hemispheric synchronization connectivity was observed over the centro-parietal, centro-occipital and parieto-occipital areas for the alpha band (p<0.05). Local graph measures showed a tDCS-induced polarity-specific differences that regarded modifications of network activities rather than specific region properties. Our results show that applying tDCS during the resting state modulates local synchronization as well as network properties in slow frequency bands, in a polarity-specific manner. •tDCS affects in a polarity specific manner the online resting state functional brain networks.•Graph theoretical approach can be used to evaluate and quantify the ongoing cortical connectivity changes induced by tDCS.•Local synchronization and connectivity patterns are modulated by tDCS, in a polarity specific manner.