A biological oscillator system and the development of sleep-waking behavior during early infancy.

The sleep-waking behavior of a male infant, normal with respect to pregnancy, delivery and Apgar score, was observed continuously from birth till the first 4 months of life. The infant was allowed to sleep and awake according to his own schedule and was fed only if his behavior could be judged as a feeding demand. Using several methods of computerized analysis it could be demonstrated that the spontaneous sleep-waking behavior was mainly driven by two endogenous rhythms, an ultradian cycle and a circadian one. While the ultradian rhythm was already established at term showing a mean period of 4 h, the circadian variation developed during the first 3 months of life. So far our results support earlier studies (KLEITMAN and ENGELMANN; PARMELEE; HELLBRUGGE,). The present paper, however, gives further evidence that both rhythms do not run independently, but seem to constitute a system of connected oscillators. As soon as the circadian rhythm is manifestly developed, the period of the ultradian rhythm seems to be modulated according to circadian variations. More specifically, during the nocturnal phase of the circadian rhythm the ultradian rhythm decelerated. By contrast, during the diurnal phase the ultradian cycle was accelerated. Using circadian frequency modulation of the ultradian cycle as the underlying principle, a computerized model of both connected oscillators was developed. The theoretically predicted sleep-waking behavior was compared to the behavior actually observed in the infant of this study. During postnatal development the coupled rhythms cause characteristic periodicities of the sleep-waking pattern. Since the infant experiences his world within a basic framework of sleep and waking spans, the different periodicities may be considered as a structure timing the information process in the developing brain.