Sleep maturation during the first two years of life: structure, quantitative approach and circadian organization.

This study presents results on sleep maturation during the first two years of life, based on a longitudinal study of 15 normal children recorded at ho me over 24 hours at the ages of 3, 6, 9, 12, 18 and 24 months. The developm ent of the different stages and parameters of sleep was studied in quantita tive, structural and circadian terms. To do so, various analyses were perfo rmed on the polygraphic recording data interpreted using the "adult" criter ia suggested by Rechtschaffen et Kales in 1968 [54]. Results show the very early presence of some adult sleep parameters, such as the stable mean dura tion of episodes of paradoxical sleep (PS), the rapid decrease in the amoun t of this sleep stage, which reaches adult levels by the age of 9 months, t he large amount of slow wave sleep in the first sleep cycle from the age of 3 months and the stability of the acrophase of the PS circadian rhythm The position of the acrophase corresponds to the period of high PS density at the end of the night in adults. Other parameters, such as the increase in s tages 1 and 2 of slow wave sleep, the increase in the latency of PS with th e disappearance at 9 months of PS onset, and the increase in stability of s leep with a decrease in nocturnal waking and body movements, are related to the maturation of the central nervous system structures implicated in the mechanisms of sleep (maturation of the thalamo-cortical pathways and the ro stro-caudal pons-thalamus connections). These maturation processes may be m arkedly influenced by the environment. Finally, the increase with age in th e amplitude of the sleep circadian rhythm may lead to both lengthening of t he sleep cycle at the age of 12 months and development of the homeostatic p rocess of sleep analysed by temporal changes in slow wave sleep. (C) 1998 E lsevier, Paris.