Cerebral cortical activity is continuous during the day and night and throughout the individual’s life. During the day, attention is directed to the outside, forming a brain-environment relationship, necessary to procure an adaptive reaction to the environment. During the night, all the cerebral force turns inside, configuring a cerebral-cerebral relation, in which sleep and dreams emerge, thus generating a virtual reality. The intestinal brain is the functional state of the brain in which it ignores external information and is attentive to the interior, to the cerebral cortex itself. In REM (rapid eye movement) state, the most vivid dreams and internal attention are developed. The REM state is the neurophysiological substrate of the intestinal brain. REM sleep is probably a specialized vigil inserted between the NOREM sleep primitive cycles.