Figure 2.

The effects of stimulus intensity level and differences across waking and sleeping states on the late auditory ERPs. These data are from the Cz electrode placement. The ERPs in NREM (stages N2 and N3) are now traced at the same scale as those in stages Wake and REM. The high amplitude N350 is therefore clipped when elicited by the 45 dB nHL stimulus. In the waking state, as stimulus intensity level was lowered, the amplitude of N1 (peaking at about 100 ms) gradually decreased. During NREM sleep, N1 was at baseline level while during REM sleep, a significant, but much reduced N1 was elicited, but only for the 45 dB nHL intensity level stimulus. On the other hand, a large amplitude P2 was apparent during NREM sleep and this deflection became gradually attenuated as stimulus intensity was reduced. A smaller amplitude P2 was apparent during REM sleep, while the P2 was much reduced during wakefulness. A very large amplitude N350 was apparent for the 35 and 45 dB nHL stimuli during NREM sleep. It was markedly attenuated during REM sleep. During all sleep stages, N350 rapidly declined in amplitude as the intensity level of the stimulus was reduced. N350 was not elicited in the waking state.