The impact of prestimulus EEG frequency on auditory evoked potentials during sleep onset

Auditory evoked potentials were recorded during wakefulness, Stage 1, and S tage 2 non-REM sleep using a three-tone auditory oddball paradigm. Stage 1 sleep was divided into trials preceded by alpha and those preceded by theta . A negative wave peaking at about 100 ms, N1, displayed a significant decr ease in amplitude with the onset of Stage 2 sleep. A later N2 peaked at abo ut 250 ms in the waking state. This changed into a sleep-specific negative wave peaking at 300 ms (N300) at the alpha-theta transition within Stage 1. The P300 displayed a similar shift to become a P450 in Stage 2 sleep. N550 was specific to Stage 2, and was larger in response to rare, rather than f requent stimuli. There was no evidence of any enhancement to relevant rare stimuli compared with irrelevant rare stimuli.