P300 to high intensity stimuli during REM sleep

Objectives: The P300 component of the auditory event-related potential (ERP) is a large amplitude positive wave peaking at approximately 300 ms following detection of a rare significant stimulus. Although P300 is typically only evoked when the subject attends to the stimulus, it may also be elicited in an awake, inattentive subject if the stimulus is sufficiently intrusive. We therefore employed an oddball task to determine if high intensity stimuli would elicit the P300 during sleep. Methods: A loud 90 dB SPL tone pip was presented infrequently (P=0.05) in a train of lower intensity 70 dB SPL standard stimuli. A multiple channel EEG was recorded from 8 good sleepers during a single night. Results: A large amplitude parieto-central P300, peaking at 321 ms, was apparent in REM sleep to the loud deviant stimulus. In stage two non-REM sleep, a later positive wave, peaking at 446 ms, was apparent even after K-Complexes were removed from the average. This non-REM P450 was however maximum over occipito-parietal areas of the scalp. Conclusion: The presence of a P300 in REM sleep following a loud, rare stimulus indicates that sensory discrimination capabilities remain intact during this state. This may be associated with either pre- or conscious processing of relevant stimuli.