Cognitive activity in sleep and responsiveness to external stimuli.

The relationship between responsiveness to auditory stimuli presented during sleep and cognitive activity during sleep was assessed. Sixteen college-aged women were instructed while awake to turn off a tone by taking a deep breath. The tone was then presented during Stage 2 and REM sleep. Subjects were awakened after select trials to assess the relationship between responding and reports of ongoing cognitive activity. Consistent with the view that cognitive activity reduces responsiveness, significantly fewer responses were found on report (cognitive activity) trials relative to no-report (no cognitive activity) trials in analyses involving all trials and Stage 2 trials alone. Trained judges then rated the subjects' reports of cognitive activity as indicating incorporation or not indicating incorporation of the tone and/or the breathing response. Incorporation was associated with a reduced likelihood of responding relative to no incorporation in analyses involving all trials. No difference in responding was found between no-incorporation trials and no-report trials, suggesting that reduced responsiveness is associated with cognitive activity only when incorporation occurs. These findings support hypotheses that the reduced responsiveness to external stimulation during sleep is at least in part due to ongoing cognitive activity.