Figure 1.

(a) Photograph of the first brown-throated three-toed sloth (B. variegatus) with an EEG/EMG recorder attached to its head. Three representative 90 s recordings of the EEG and EMG activity from a sloth showing (b) a transition (black arrowhead) from non-REM sleep to wakefulness, (c) a transition (black arrowhead) from non-REM to REM sleep and (d) a period of stable REM sleep. In contrast to wakefulness and REM sleep, the EEG during non-REM sleep exhibits high-amplitude, low-frequency activity. REM sleep is distinguished from wakefulness by the low-amplitude EMG activity, intermittently interrupted by brief high-amplitude twitches. The respective amplitude scales for the EEG and EMG recordings are the same in (b)–(d).