Abstract
The echidna, an egg-laying mammal with alow (31–33 °C) body temperature, does not show paradoxical sleep (PS). The purpose of this study was to determine whether PS can occur at low body temperatures in a placental mammal. The nine-banded armadillo is a species reputed to have a low body temperature and poor temperature regulation. However, we found that at moderate (22–26 °C) ambient temperatures, brain temperature ranged from 34 to 36 °C, higher than in the echidna. Reduction of body temperature was therefore attempted in four animals during long-term recordings at low (10–15 °C) ambient temperature. PS was clearly seen in two animals whose brain temperatures dropped below 33 °C. We conclude that low brain temperature per se does not prevent the occurrence of PS and is not causally related to its absence in the echidna. Normative sleep characteristics were also determined. Polygraphic characteristics of waking, slow wave sleep, and PS were in general typically mammalian. The armadillo is a behaviorally deep sleeper, spending over 17 h per day asleep, of which about 18% is spent in PS.