A natural reduction of consciousness during sleep alters the correlation between components of the default-mode network (DMN), particularly reducing the involvement of frontal cortex. This suggests the DMN may play an important role in sustaining conscious awareness. The finding contrasts with a recent study in anesthetized primates that proposed DMN activity reflects general network dynamics rather than conscious mentation.
REM sleep is a distinct state of consciousness with brain activity levels similar to wakefulness but radically different conscious awareness. Using fMRI, researchers observed that the default mode network (DMN), which reflects level of consciousness, becomes functionally uncoupled during deep sleep but recouples during REM sleep, resembling wakefulness. Unlike deep sleep or wakefulness, REM shows widespread, temporally dynamic interactions between unimodal sensorimotor areas and higher-order association cortices, including the DMN. These two systems become anticorrelated and fluctuate rhythmically in alternating multisecond epochs at 0.1 to 0.01 Hz, suggesting a model relevant to dream formation and memory consolidation.