The effect of sleep onset on event related potentials with rapid rates of stimulus presentation

Amplitude changes to the auditory P1-N1-P2-N2 event-related potential (ERP) complex were measured during sleep onset (SO). A rapid rate of stimulus presentation (every 600 ms) was employed. Eight young adults were tested during alert wakefulness, relaxed wakefulness, and during Stages 1, 2, 3 and 4 of sleep. Subjects were repeatedly awakened and the procedure replicated to ensure a sufficient number of trials were presented within each of the sub-intervals. A large fronto-central P1-N1-P2-N2 complex was observed in the Alert Wakefulness condition. A negative slow wave that overlapped the P1-N1-P2 complex became increasingly attenuated as the subject became more drowsy and finally entered sleep. N1 thus became increasingly attenuated and P1 and P2 increasingly augmented during sleep onset. This difference attained statistical significance during Stage 1 of sleep. N2 did not increase in amplitude at SO, as has been reported in other studies.