The ontogeny of sleep in kittens and young rabbits

Abstract

1. 1. The development of sleep in thirty-eight kittens (from 1 to 87 days of age) and in thirty-two rabbits (from 1 to 47 days of age) was studied by means of recording of the EEG, EMG of the posterior neck muscles, respiration as well as observations of gross behavior. 2. 2. The similarities between sleep with jerks in very young animals (kittens 1–12 days of age, rabbits 1–3 days of age) and “activated” sleep in the older animals (kittens up to 87 days, rabbits 47 days) were confirmed. 3. 3. The episodes of “activated” sleep (sleep with jerks) as well as those of slow wave sleep (calm sleep) were short lasting and occurred very frequently at birth. They became longer but less frequent with growth. At certain ages, earlier in rabbits (4–6 days) than in kittens (22–27 days), the lengthenings of single episodes of “ractivated” sleep reached their plateaus. Almost at the same respective ages as above for each species, the decrease of incidences of slow wave sleep episodes attained their plateaus. Thereafter, “activated” sleep episodes occurred with rather constant durations but their incidences continued to decrease with further growth. In contrast, slow wave sleep episodes were observed in faily constant incidences but each single episode kept lenghtening in durations with growth. As a consequence of these changes, the percent durations of “activated” sleep in total sleep time had decreased with age. Accordingly, those of slow wave sleep increased. 4. 4. All of these changes with age; i.e., diminution of percent durations of “activated” sleep, lengthening of single episodes of both phases of sleep and decrease in the incidences of both phases of sleep, were practically completed by 22–24 days of age in rabbits and 65–67 days in kittens. It is also shown that sleep patterns of rabbits matured much earlier than those of kittens in every respect.