Dissociation of alpha and theta activity as a function of verbal and visuospatial tasks.

EEG was recorded from P3 and P4 in 12 male subjects during a rest condition and while they performed a verbal and a visuospatial task. Power in the alpha and theta bands was derived from EEG epochs associated with task-related cognitive activity uncontaminated by response activity. Alpha power was significantly lower during performance on both tasks compared to the rest condition, but did not differ between tasks or hemispheres. Conversely, theta power was significantly higher during task performance, and, in the right hemisphere only, was higher in epochs recorded during the visuospatial as opposed to the verbal task. This difference between the tasks in right hemisphere theta correlated significantly with level of visuospatial performance as, to a lesser extent, did differences in left hemisphere theta. These results are discussed in terms of the sensitivity of different regions of the EEG spectrum to cognitive activity underlying performance on different types of task.