The mismatch negativity during natural sleep: Intensity deviants.

Evaluated the sensitivity of the intensity mismatch negativity (MMN) to attention by recording event-related potentials (ERPs) to auditory intensity changes during sleep. Auditory ERPs were recorded from 7 Ss (aged 19-31 yrs) over a single night in the laboratory. An "oddball" sequence of brief tone pips, differing in intensity, was used. Frequently occurring 70 dB "standards" were presented with infrequent 80 dB intensity increment deviants and 60 dB intensity decrement deviants. Stimuli were presented in a random sequence every 600 ms while Ss were awake but inattentive and during stages 2 and REM of sleep. During wakefulness, the intensity increments elicited a broad fronto-central negativity with 2 discernable peaks. The first, peaking at approximately 120 ms, showed a polarity inversion at the mastoid and likely represented a summation of the N1 wave and the 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 negativity but its amplitude was not significantly larger than the baseline level. It was followed by a larger and significant 300-450 ms negativity but this was considered too delayed to represent the MMN