[The ontogeny and physiology confirms the dual nature of sleep states].

In the Jouvet's laboratory, as early as 1960 the study of the ontogenesis of paradoxical sleep (PS) named "sleep 'with jerks" began in the kitten and led to the first publication in 1961. Then, several species were studied, lamb, rat, human neonates, etc. These works showed that at birth sleep with jerks was preponderant in altricial (immature) species (cat, rat) and the first to appear during the second half of gestation in precocious species (guinea pig). For Jouvet, sleep with jerks is a immature form of PS. Why PS is so important at birth? The maturation of the central nervous system, based on the myelinization, starts in the spinal cord then forwards to the brainstem and forebrain. So, PS mechanisms located in the brainstem are the first to mature and the only one to function. Then the slow wave sleep (SWS) and waking structures become mature. Phylogenetic studies showed that in mammals and birds PS was present even in marsupials and monotremes. Until now only the one exception is the dolphin with a voluntary breathing. To sleep and breath, dolphin has developed an unilateral sleep without classical PS. In other animals, reptiles, amphibians, fishes, PS was not observed with the parameters used in mammals. The study at birth (not yet done) of reptiles would allow perhaps the observation of a temporary PS. Based on these findings, a schematic model of the sleep regulation can be elaborated. Haeckel's aphorism "Ontogeny recapitulates phylogeny" seems true for PS which appears in birds and mammals i.e. at the end of evolution as it appears at the end of gestation when PS cerebral structures are present and mature.