Event-related alpha oscillations in task processing

Objectives: Recent findings substantiate the view that electroencephalographic (EEG) alpha rhythm (7-13 Hz) is functionally involved in information processing. However, the association of alpha rhythms with cognitive brain processes is less well understood because both augmentation and suppression of alpha oscillations have been observed to accompany task performance. The present study evaluates the effect of task processing on event-related alpha oscillations at the level of single-sweep analysis. Methods: EEG was recorded from Fz, Cz and Pz electrodes in 10 subjects participating in two experimental sessions, in which auditory stimuli with equal physical parameters were presented under different instructions (passive and task). Separate measurements of single-sweep amplitude and phase-locking were performed and statistically analyzed for consecutive time windows in the poststimulus epoch. Results: Major results show that, during the cognitive task, the phase-locking of alpha oscillations at the frontal site is significantly increased for the time window of 500-1000 ms after stimulation. Conclusions: The involvement of enhanced and synchronized frontal alpha activity in higher brain processes is strongly emphasized. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.