Neurophysiological Evidence for the Detection of External Stimuli During Sleep

STUDY

Objectives: A cognitive evoked potential, labelled "P300," is elicited when an observer attends to and detects an infrequently delivered "target" stimulus. It is not typically present if the target is ignored or undetected. P300 is therefore thought to reflect some aspect of consciousness of the stimulus. There has been much controversy concerning whether P300 can be recorded in sleep, a state in which information processing of external events is presumably reduced. The present study investigated the effects of both pitch and intensity stimuli on information processing, in order to determine whether a more salient stimulus might elicit a P300 in sleep that is comparable to the waking P300.

Design: A true P300 will have a parietal maximum peak following a rare stimulus, and its amplitude will vary inversely with the probability of stimulus delivery. Participants were thus randomly assigned to one of three probability groups, in which the deviant was presented on 20%, 10%, or 5% of trials.

Setting: Data were collected in the Human Neurophysiology Laboratory at the University of Ottawa.

Participants: Twenty-four young adults.

Interventions: N/A.

Measurements: AND

Results: During wakefulness, a parietal P300 was apparent following both pitch and intensity deviants when participants were asked to detect deviant stimuli. A P300 was also apparent following the intensity deviant when participants were instructed to ignore the stimuli. During non-REM sleep, no P300 could be identified. In REM sleep, very rare (p=.05) loud deviants elicited a parietal P300. This P300 was attenuated relative to the waking ignore condition. Moreover, the frontal dispersion of the peak was absent.

Conclusions: These data provide evidence that participants are conscious (parietal P300) of very rare and intrusive stimuli during REM sleep, although the frontal aspects associated with this consciousness may be absent.