USING an oddball paradigm with two tones differing in pitch and probab
ility, event-related potentials (ERPs) were compared during wake and t
wo sleep stages. REM and NREM sleep stages were identified in nine sub
jects using the Nightcap which continuously records eye and body movem
ents. The N1 occurred later and the P2 was larger during sleep than wh
en awake. The NT to the infrequent tones was larger during both sleep
stages. A fate negative wave was significantly larger to infrequent to
nes during REM sleep. It is concluded that representations of auditory
, during the REM phase. The prolonged latency of the ERP components in
dicates that processing of external sensory stimuli may be delayed.