The mismatch negativity to frequency deviants during the transition from wakefulness to sleep

This study examines the changes in the Mismatch Negativity during the trans ition from a waking conscious state to one of sleep and unconsciousness. Au ditory event-related potentials were recorded from eight participants durin g the sleep onset period. A 1,000 Hz-standard stimulus was presented every 600 ms. At random, on 20% of the trials, the standard was changed to either a large 2,000-Hz or a small 1,100-Hz deviant. During wakefulness, the larg e deviant elicited a larger, long-lasting MMN than the small deviant. Follo wing the large deviant during relaxed wakefulness and Stage 2 sleep, the MM N continued to be elicited although it was reduced in amplitude. No signifi cant MMN was recorded for either deviant in Stages 1 and slow wave sleep. T he loss of consciousness therefore appears to have a marked effect on the M MN.