SLEEP ONTOGENY REVISITED - A LONGITUDINAL 24-HOUR HOME POLYGRAPHIC STUDY ON 15 NORMAL INFANTS DURING THE FIRST 2 YEARS OF LIFE

The sleep organization of 15 normal infants (seven boys, eight girls) was studied at their homes during six 24-hour periods, i.e. at 3, 6, 9 , 12, 18, and 24 months of age, using the Oxford Medical System. Sleep states and stages were scored visually at 30-second intervals, accord ing to Rechtschaffen and Kales' criteria, adapted for children by Guil leminault. All sleep parameters were analyzed for the entire 24-hour p eriod, i.e. during both the nocturnal and the diurnal part of the nyct hemere. The results showed a continuous decrease in total sleep time, rapid eye movement (REM) sleep, and indeterminate sleep, and also an i ncrease in waking time, quiet sleep, and stages 1 and 2 sleep. Except for slow-wave sleep, which remained very stable for the different ages , analysis of variance applied to the data showed clear age and day-ni ght effects on sleep ontogenesis. Modifications with age were more pre cocious and more pronounced for the diurnal part of the nycthemere, es pecially as regards REM sleep. For the nocturnal part, there was a sig nificant increase in sleep efficiency and in the length of the REM per iod after 12 months of age, while total sleep duration and number of a wakenings decreased. In addition to normative data for clinical use, t his study provides three new interesting results related to the matura tion of sleep mechanisms and functions: 1) the high stability of the p ercentage of slow-wave sleep along these 2 years, 2) the presence (fro m 12 months of age) of a stage 2/REM sleep ratio equal to one, and a s leep change occuring earlier, during the diurnal rather than the noctu rnal part of the nycthemere. The first two points could be regarded as indexes of sleep maturation reflecting developmental and neurophysiol ogical changes in central nervous system structures. The third point u nderlines the importance of the circadian rhythm and the concept of '' experience'' in the maturation of sleep.