Influence of tACS/tDCS on resting state effective connectivity in the frontal cortex: An functional near-infrared spectroscopy study

Bidirectional connectivity has been used to examine the influence of electrical or magnetic stimulations, using functional connectivity obtained from correlations in a time-averaged manner throughout a task or at rest. However, the resultant connectivity matrices may give high correlations in the case of brain imaging data and might miss the directional information. In this study, effective connectivity obtained from Granger Causality will be used to investigate the influence of stimulation. Functional near-infrared spectroscopy is used to obtain the resting state data from the prefrontal cortex of fifteen healthy participants with two stimulation techniques in this investigation. The network matrices were created using fNIRS data of pre, during, and post-stimulation phases. The impacts of stimulation were compared using temporal hemodynamics data and connectivity alterations. Both stimulation strategies were observed to boost hemodynamic responses, which remained elevated for a time after the stimulation halted. It was observed that a significant increase in effective (p < 0.05) but not functional (p > 0.05) connectivity between distinct areas of the prefrontal cortex. The findings of this study can be more enhanced and could be applicable in clinical trials for the treatment of patients with neurological diseases.