EVENT-RELATED GAMMA-BAND ACTIVITY DURING PASSIVE AND ACTIVE ODDBALL TASKS

THE EEG was recorded during passive listening and active attending to tone pips of an oddball stimulus sequence, and the time course of even t-related gamma band activity (30-60 Hz) was compared with event-relat ed potential (ERP) components. In the conventional frequency range (0. 1-43 Hz) mismatch negativity (MMN) was produced in the passive listeni ng condition. Concurrent with MMN, the power of event-related gamma ac tivity to the deviant stimulus was higher than gamma activity elicited by the preceding standard stimulus. The transition from the N2b to th e P3 wave, produced during active attention, was associated with a dec rease in gamma band power upon the deviant tone. The results show the differential generation of gamma band power depending on preattentive and attentive stimulus processing.