Ontogenesis of the states of sleep in rat, cat, and guinea pig during the first postnatal month

The behavioral and polygraphic characteristics of wakefulness and sleep were studied in 20 infant rats, 26 kittens, and 25 infant guinea pigs during their first month of postnatal life. In the infant guinea pig, the electrocorticographic (ECoG) patterns of sleep were similar to those of the adult, except for the absence of spindles during the first 3 weeks. In the rat and the cat, states of vigilance were not clearly differentiated in ECoG patterns during the first week; near the 8th day a fast, high amplitude ECoG appeared during paradoxical sleep (PS). The first signs of slow‐wave sleep (SWS) appeared at 11 to 13 days of age in the rat and at 15 to 21 days in the cat. The greater the immaturity of the animal at birth, the greater was the amount of time spent in PS in the perinatal period. In the rat, which was born the most immature, the decrease in the percent time of PS was very rapid: 70 % at birth, it decreased to 12% on the 30th day. In the cat the decrease was slower. In the guinea pig, despite its relative maturity, the percent time of PS at birth was 7%, approximately double that in the adult. The length of extrauterine life as well as the degree of immaturity at birth, played a role in the development of the sleep‐wakefulness cycle.