Evoked phase synchronization between adjacent high-density electrodes in human scalp EEG: Duration and time course related to behavior

Objective Data from a previous event-related potential (ERP) study in visual-perceptual grouping [Nikolaev AR, van Leeuwen C. Flexibility in spatial and non-spatial feature grouping: an event-related potentials study. Brain Res Cogn Brain Res 2004;22:13–25] were re-analyzed to identify event-related dynamics of phase-synchronization. Methods In 20 Hz activity, uniform spreading of phase synchronization in closely spaced ( 2 cm) scalp electrodes appears and disappears spontaneously. The lengths of synchronized activity intervals and how they vary as a function of stimulus presentation were compared between task and control conditions. Results Synchronization reached a maximum in the task condition about 180 ms post-stimulus onset, coinciding with the peak N180 ERP marking the deployment of task-specific attention. Synchronized intervals were longer in the task than in the control condition. Long (above 80 ms) intervals occurred at a stable rate before and just after stimulus onset, but steeply decreased 200–400 ms afterwards. Conclusions Perceptual tasks lead to longer synchronized intervals in early visual areas. Attention deployment resets the ongoing synchronization. Event-related activity, besides low-frequency ERP, consists of high-frequency short and long synchronized intervals corresponding to evoked bursts and ongoing oscillations, respectively. Significance High-density scalp recorded EEG revealed synchronization dynamics in a local, early visual area of cortex that can be interpreted as modulation of spontaneous ongoing task-related processes by attention.