Electrographic correlates of sleep behavior in a primitive mammal, the armadillo Dasypus novemcinctus

Abstract

Sleep behavior in 5 armadillos was studied over a continuous 24-hr period in order to evaluate certain hypotheses concerning the relation of life style and phylogenetic rank to sleep. The physical security of a sleeping armadillo, according to a life style hypothesis, should allow it to sleep extensively and to have a high proportion of paradoxical sleep (PS). In this study armadillos slept an average of over 77% of the day. Armadillos apparently are phylogenetically advanced enough to display PS and, depending on criteria and data interpretation, were observed to spend approximately 8.9%–21.5% of their sleep time in PS. During the short and scattered wakefulness periods armadillos were vigorously active, with no periods of awake quiescence lasting more than 2 min. Sleep onset was unusually sudden, occurring in 11–19 episodes per day. Rectal temperatures varied erratically over a wide range and did not correlate with behavioral state. The typical slow wave EEG pattern occurred about 50% of the total sleep time, with durations of a given period ranging from 0.75–375 min. Activated EEGs during sleep were associated with 4 different categories of rapid eye movement and neck muscle activity. Activated EEG episodes ranged from 0.8–1.6 min and were interspersed with abrupt transitions among the slow wave periods. Analysis of PS was confounded by the short periods of activated EEGs and by the absence of nuchal atonia. At least some of the categories of activated EEG could have reflected shivering or transient arousal from slow wave sleep, rather than PS.