How ‘REM sleep’ is paradoxical in human

Abstract

Although brain activity has some similarity during paradoxical sleep and wakefulness, it differs in many aspects. Thalamic and cortical activities, time-locked throughout wakefulness and slow wave sleep, are different during paradoxical sleep, that of the thalamus being in the delta range while that of the cortex being rapid. This decoupling of thalamo-cortical activity may participate to phenomena such as altered experience during dream or hypnagogic hallucinations in narcolepsy. Detection of verbal discordance is preserved during PS, but with a different process that of waking, responses to pseudo-words being similar to those to congruous words. Linguistic absurdity appears to be accepted in a different manner during paradoxical sleep than during waking, and this might explain why absurd contents are so naturally incorporated into otherwise plausible dream stories. In responses to nociceptive stimuli, while the lateral operculo-insular system subserving sensory analysis of the stimuli remained active during paradoxical sleep, mid-anterior cingulate processes related to orienting and avoidance behavior are suppressed. Dissociation between sensory and orienting-motor networks might explain why nociceptive stimuli can be either neglected or incorporated into dreams without awakening the subject.