Auditory-evoked responses influenced by presence or absence of EEG alpha activity and actual cognitive state.

The presence or absence of alpha activity in occipital EEG was detected automatically. Auditory-evoked responses (AERs) related to these two brain states and at the same time to different perceptual-cognitive situations (passive listening, discrimination between two tones and pressing the button accordingly similar discrimination without motor reaction) were analyzed and compared statistically. The main result was that during the alpha state (and not during the non-alpha state, when EEG was desynchronized), the amplitudes of N1, P1 waves and peak-to-peak amplitudes N1-P2 were higher during passive listening to stimuli in comparison with the active perceptual-cognitive states mentioned. No differences in latencies of AERs were found.