Figure 1.

Grand averaged (n = 10) ERPs following presentation of the 45 dB nHL intensity level stimulus during the waking (left column) and sleeping states. ERPs elicited during NREM sleep (stages N2 and N3) are traced in the middle columns. Stage N2 is divided into its early (solid line) and late (dashed line) halves, based on time of night. ERPs elicited during REM sleep are traced in the right column. In this and all other figures, negativity at the scalp relative to the mastoid reference is indicated by a downward deflection. Note the differences in the calibration signal in stages Wake and REM compared to stages N2 and N3. This is to allow visualization of large ERP deflections elicited during stages N2 and N3. A large centro-frontal N1 was apparent in the waking state, when subjects were asked to ignore the auditory stimuli. N1 was much reduced during REM sleep and was at pre-stimulus baseline level during NREM sleep. On the other hand, only a small amplitude P2 was elicited during wakefulness but a much larger P2 was apparent during NREM sleep. A very large amplitude central negativity, peaking at about 350 ms was apparent during stages N2 and N3. The amplitude of this N350 was much reduced during stage REM. N350 was not apparent in the waking state.