EEG and slow cortical potentials in anticipation of mental tasks with different hemispheric involvement.

Mental arithmetic is supposed to be processed by the left hemisphere, while pattern matching has been considered to be processed by the right hemisphere. These different mental tasks were presented to 16 right-handed male subjects. As a variable task difficulty was varied for the two task categories. The task presentations were preceded by 6 sec warning stimuli which indicated the level of difficulty of the task. EEG and slow cortical potentials (SCPs) were recorded from temporal and precentral leads of both hemispheres. The reference was noncephalic. During the anticipation interval beta-activity was enhanced above the hemisphere primarily involved in the particular task. SCPs failed to show a comparable clear pattern. A late negative component showed task-dependent asymmetries prior to easy tasks, but not prior to difficult tasks.