Alpha power dependent light stimulation: dynamics of event-related (de)synchronization in human electroencephalogram.

The desynchronization and resynchronization of alpha oscillations was studied in 10 normal subjects after visual stimulation of both eyes under two experimental conditions, "eyes opened" and "eyes closed". The electroencephalogram (EEG) was recorded bipolarly over the occipital area and sampled at 200 Hz. The data was processed in real time and evaluated online. In accordance with the alpha power in the 7 to 13 Hz band, short red light flashes of 10 ms duration were presented at intervals of at least 2 s. This stimulation resulted in an event-related desynchronization (ERD) followed by resynchronization. Trials were controlled for artifacts, averaged offline, and the amount of event-related (de)synchronization was calculated. The event-related desynchronization was significantly larger in the eyes open paradigm. In addition, the latencies of event-related desynchronization and resynchronization maxima were larger in the eyes open paradigm compared to the eyes closed one.