Reduction of somatosensory functional connectivity by transcranial alternating current stimulation at endogenous mu-frequency

Alpha, the most prominent human brain rhythm, might reflect a mechanism of functional inhibition for gating neural processing. This concept has been derived predominantly from local measures of inhibition, while large-scale network mechanisms to guide information flow are largely unknown. Here, we investigated functional connectivity changes on a whole-brain level by concurrent transcranial alternating current stimulation (tACS) and resting-state functional MRI in humans. We specifically focused on somatosensory alpha-band oscillations by adjusting the tACS frequency to each individual´s somatosensory (mu-) alpha peak frequency (mu-tACS). Potential differences of Eigenvector Centrality of primary somatosensory cortex (S1) as well as on a whole brain level between mu-tACS and sham were analyzed. Our results demonstrate that mu-tACS induces a locally-specific decrease in whole-brain functional connectivity of left S1. An additional exploratory analysis revealed that this effect primarily depends on a decrease in functional connectivity between S1 and a network of regions that are crucially involved in somatosensory processing. Furthermore, the decrease in functional centrality was specific to mu-tACS and was not observed when tACS was applied in the gamma-range in an independent study. Our findings provide evidence that modulated somatosensory (mu-) alpha-activity may affect whole-brain network level activity by decoupling primary sensory areas from other hubs involved in sensory processing.