Independent component analysis of resting brain activity reveals transient modulation of local cortical processing by transcranial direct current stimulation.

Neuroplasticity induced by transcranial direct current stimulation (tDCS) contributes to motor learning although the underlying mechanisms are incompletely understood. Here, we investigated the effects of tDCS on resting brain dynamics recorded by whole-head magnetoencephalography (MEG) pre- and up to 35 minutes post-tDCS or sham over the left primary motor cortex (M1) in healthy adults. Owing to superior temporal and spatial resolution of MEG, we sought to apply a robust, blind and data-driven analytic approach such as independent component analysis (ICA) and statistical clustering to these data to investigate potential neuroplastic effects of tDCS during resting state conditions. We found decreased alpha and increased gamma band power that outlasted the real tDCS stimulation period in a fronto-parietal motor network relative to sham. However, this method could not find differences between anodal and cathodal polarities of tDCS. These results suggest that tDCS over M1 modulates resting brain dynamics in a fronto-parietal motor network (that includes the stimulated location), indicative of within-network enhanced localized cortical processing.