Increased frontal phase-locking of event-related alpha oscillations duringtask processing

Recent findings substantiate the view that electroencephalographic (EEG) al pha rhythm (7-13 Hz) is functionally involved in cognitive stimulus process ing. Our previous results have shown that enhanced alpha responses to audit ory task stimuli can be well synchronized with stimulus until 800-1000 ms. The present study analyzed the effect of perceptual uncertainty and difficu lty in decision making on event-related alpha oscillations in single audito ry event-related brain potentials (ERPs). EEG was recorded from Fz, Ct and Pt electrodes in 10 subjects participating in two experimental sessions, in which auditory stimuli with equal physical parameters were presented under passive and task instructions. Separate measurements of single alpha respo nse amplitude and phase-locking were performed and statistically analyzed f or consecutive time windows in the post-stimulus epoch. Major results show that, during the cognitive task, the phase-locking of alpha oscillations at the frontal site is significantly increased in the time window of 500-1000 ms after stimulation. Thus, the involvement of enhanced and synchronized f rontal alpha activity in higher brain processes is strongly emphasized. (C) 2001 Elsevier Science B.V. All rights reserved.