Functions and sources of event-related EEG alpha oscillations studied with the Wavelet Transform

Objectives: By using the Wavelet Transform, a time frequency representation with nearly optimal resolution, we studied responses to stimulation in the ‘alpha’ range (10 Hz). Methods: Visual evoked responses of 10 healthy subjects were studied with 3 different stimulus types (no-task VEP, non-target and target stimulus). Results: Upon all the stimulus types, event-related responses in the 10 Hz (‘alpha’) range were distributed in the whole scalp, best defined in the occipital locations, the responses on the anterior electrodes being less pronounced and delayed. In some subjects, these event-related responses were prolonged upon target stimulation in posterior locations. Conclusions: These results point towards a distributed origin of event-related alpha oscillations with functional relation to sensory processing, and possibly to further processes.