[Ontogenesis and organization of sleep]

The newborn infant spends three quarters of his time asleep, while at adulthood his sleep will occupy only 8 hours out of 24. The development of sleep and wakefulness is continuous from before to after birth, and follows a progressive pattern: first rapid in the perinatal period and until one year of age, then much slower until puberty. Schematically, the ontogenetic organization of the states of vigilance consists of: 1. the building up of a circadian sleep-wake rhythm and the lengthening of the ultradian Basic Rest-Activity Cycle, 2. the specific development of each physiological variable which is linked to the states, 3. the synchronization of these variables, and 4. the reduction of REM sleep time and the relative increase of non-REM sleep proportion. This ontogenetic scheme applies by in large to all mammals. It raises the fascinating question of the role of REM sleep and of dreaming in the evolution of the organism and of the species.