Causal modulation of right fronto-parietal phase synchrony with Transcranial Magnetic Stimulation during a conscious visual detection task

Correlational evidence in non-human primates has reported evidence of increased frontoparietal high-beta band (22-30 Hz) synchrony during the endogenous allocation of visuospatial attention. But may the engagement of inter-regional synchrony at this specific frequency band provide the causal mechanism by which top-down processes are engaged and they facilitate visual perception in humans? Here we further analyzed electroencephalographic (EEG) signals from a group of healthy human participants who performed a conscious visual detection task, under the influence of brief rhythmic (30 Hz) or random bursts of Transcranial Magnetic Stimulation (TMS), with an identical number of pulses and duration, delivered to the right Frontal Eye Field (FEF) prior to the onset of a lateralized near-threshold target. We report increases of inter-regional synchronization in the high-beta band (25-35 Hz) between the electrode closest to the stimulated region (right FEF) and parietal leads, and increases of local inter-trial coherence in the same frequency band over parietal contacts, both driven by rhythmic but not random TMS patterns. Importantly, such increases were accompained by increases of visual sensitivity for left visual targets (contralateral to the stimulation) in the rhythmic but not the random TMS condition at the group level. These outcomes suggest that human high-beta synchrony between right frontal and parietal regions can be modulated non-invasively and that high-beta oscillatory activity across the right dorsal fronto-parietal network may contribute to the facilitation of conscious visual detection. Our study also supports future applications of non-invasive brain stimulation technologies for the manipulation of inter-regional synchrony, which could be administered to improve visual behaviors in healthy humans or neurological patients.