The mismatch negativity during natural sleep: intensity deviants

Auditory event-related potentials (ERPs) were recorded from 7 subjects who slept for a single night in the laboratory. An 'oddball' sequence of brief tone pips, differing in intensity, was used. Frequently occurring 70 dB 'st andards' were presented with infrequent 80 dB intensity increment deviants and 60 dB intensity decrement deviants. The probability of each deviant was 0.1. Stimuli were presented in a random sequence every 600 ms while subjec ts were awake but inattentive and during stages 2 and REM of sleep. During wakefulness, the intensity increments elicited a broad fronto-central negat ivity with two discernable peaks. The first, peaking at approximately 120 m s, showed a polarity inversion at the mastoid and likely represented a summ ation of the N1 wave and the mismatch negativity (MMN). The second, peaking at approximately 330 ms, may have reflected an enhanced N2b component. In REM sleep, the increment deviants elicited a small amplitude 100-200 ms neg ativity but its amplitude was not significantly larger than the baseline le vel. It was followed by a larger and significant 300-450 ms negativity but this was considered too delayed to represent the MMN. The decrement deviant s elicited a small amplitude, but statistically non-significant, MMN-like w ave during both wakefulness and in REM sleep. A MMN-like wave was absent in stage 2 sleep. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.