It is well known that total sleep deprivation leads by unavoidable death of animals.Multiple visceral disorders, and first of all in the gastrointestinal system, follow sleep disturbances also in humans.However, basic studies of sleep were mainly focused on various aspects of cerebral functions.It is recognized that during slow wave sleep (SWS) cortical neurons change their firing mode to synchronized burst-pause pattern reflected in slow waves in EEG.It is recognized that propagation of sensory information to the cerebral cortex is strongly suppressed during sleep as well as the propagation of signals from the cortical motor areas to muscles-sleep atonia.However, it stayed unclear how all those changes in cortical neuronal activity associated with sleep could be related to visceral health, and why sleep deprivation leads to severe visceral disorders.To combine these contradictive effects in a single theory we proposed that during sleep the same cortical areas (and the same neurons), which during wakefulness are involved in processing of the exteroceptive information (visual, auditory, somatosensory), switch to the processing of interoceptive information, coming from the various visceral systems.Within the frame of this theory rhythmic cortical activity during SWS can be defined by periodic activity of various visceral systems (heart beats, respiration, gastro-intestinal peristaltic activity and so on).To check this theory relationship between the gastrointestinal system and cortical sensory areas was studied in sleepwake cycle.Experiments were performed in cats, rabbits and monkeys.It was shown that during SWS electrical and magnetic stimulations of the area of stomach and small intestine lead to neuronal and EEG evoked responses in various cortical sensory areas, including primary visual area V 1.All these responses disappeared immediately in wakefulness.It was demonstrated that during SWS natural myoelectrical activity of duodenum and stomach reflects in neuronal activity in cortical visual areas, and that some cortical neurons demonstrated selectivity to particular types of intestinal rhythms.It was shown that cortical neuronal firing during SWS depends on gastric content.All those observations gave strong support to the idea that during sleep the brain switches to the processing of the visceral information.This study was supported by RFBR grant No.10-04-00844.