Local phase synchronization of event-related activity modulated by visual attention

In a visual task using 12 healthy subjects, spread of evoked phase-synchronized activity was studied in local cortical areas. The areas were identified in a previous study of the same data set using event-related potentials (ERP). Chains of closely spaced (∼2 cm) scalp electrodes covering these areas were selected for phase synchronization analysis in which task and control conditions were compared. Phase synchronization spreading in the task condition at 20 Hz reached a maximum about 180 ms post-stimulus in the right occipital area. This maximum coincides with the attention-related negative peak N180 in the corresponding ERP study. Intervals of evoked phase synchronization were longer in the task than in control condition. It was concluded that attention-related modulation of evoked activity is reflected not only in enhanced amplitude of low-frequency ERP, but also in phase synchronization of high-frequency ongoing rhythms in local brain areas.