Sleep: Implications for Theories of Dreaming and Consciousness

Sleep is composed of two main stages, rapid eye movement (REM) sleep and non-REM sleep, each of them generated by specific cerebral networks. REM sleep is the behavioral state that produces the greatest recall and intensity of dreaming. Moreover, correlations between functional patterns of brain activity during REM sleep and specific properties of dream content have been emphasized, in an attempt to characterize the neural basis of dreaming. Fading of consciousness occurs in non-REM sleep, in parallel with a breakdown in cortical connectivity, but does not prevent external sensory information to be processed in the sleeping brain.