Interactions of endogenous rhythms during postnatal development. Observations of behaviour and polygraphic studies in one normal infant.

The spontaneous sleep-waking behaviour of a male infant, normal with respect to pregnancy, delivery and Apgar score, was observed continuously from birth till the first four months of life. Additionally sleep stages were registered polygraphically during several weeks. The infant was allowed to sleep and awake according to his own schedule. It could be demonstrated that the spontaneous sleep-waking behaviour was mainly driven by 3 endogenous rhythms : The Basic rest activity cycle with a period of about 50 minutes, a 4-hour cycle already established during the first 2 weeks of life and a circadian rhythm which developed during the second month of life. So far the presented results support earlier studies of Kleitman and Engelmann, Sterman and Hoppenbrouwers, Hellbrugge etc. The present study, however, gives further evidence, that these rhythms do not run independently, but constitute a system of interacting oscillators.