Development of sleep state patterns in the kitten

Abstract

In the present study the maturation of states of sleep in kittens from birth to 6 weeks of age was evaluated in terms of the developmental emergence of temporal concordance between defining physiological parameters. In addition, periodicity of the earliest alternation of states, the REM-non-REM (rapid eye movement-nonrapid eye movement) or “basic rest activity cycle”, was traced during this same interval. Parameters studied included EEG, eye movements, neck EMG, gross motor activity, and respiration patterns. Kittens were monitored in isolation for periods of 2–6 hr, providing for collection of both longitudinal and cross-sectional data. Statistical and computer analyses were performed on these data. The most outstanding feature of polygraphic data from kittens between birth and 4 weeks of age was the gradual coalescence of initially discordant physiological measures of sleep state. Prior to 3 weeks of age, polygraphic patterns differed significantly from those of the adult cat, indicating that individual rates of maturation existed for each physiological system measured. Sleep state periodicity was weak at this time due to marked pattern fragmentation. Detectable cycles were clearly shorter than those observed in the adult cat. These findings suggest that the developmental assessment of polygraphic pattern concordance might be a more useful index of sleep state maturation than evaluation based upon attempted comparisons with stable adult patterns. They suggest further that sleep state development in the kitten consists of several different stages. The initial maturation of a basic rest activity cycle may begin during gestation, and be disrupted by the transition to extrauterine life. A postnatal period of approximately 3–6 weeks is required for maturation of sensorimotor and respiratory functions in the completion of this stage. It is proposed that from this time to approximately 3 months of age, forebrain maturation and environmental influences progressively mediate a mature sleep-wake cycle which is superimposed upon this more basic level of organization.