Several 24-hour recordings of EMG,EKG, EOG, and EEG as well as behavioral observations were made on 7 adult tortoises (Testudo denticulata), Two distinct electrophysiological states were observed: (1) high tonic and phasic EMG associated with low voltage fast frequency (predominantly 6–10 cps, <40 µV) EEG activity and a heart rate of20–30 beats/min; (2) reduced tonic EMG, an EEG of high voltage (60–150 µV) spikes superimposed upon LVF activity and a decreased heart rate (10–20 beats/min). Spikes were present in the olfactory bulb, cerebral hemispheres and/or optic lobes and were manifested singly or in irregular multiphasic bursts or as a single saw-tooth-shaped wave usually associated with a spike in another region of the brain. EEG spiking was present during behaviorally inactive periods and disappeared upon arousal. Thresholds of arousal did not differ between these two electrophysiological states. Rate of EEG spiking and to some extent heart rate and EMG activity were directly related to the ambient temperature. All spiking disappeared when the temperature was lowered to 16 °C; spikes over the optic lobes exhibiting the greatest persistence. Behavioral postures of heliothermic reptiles such as the tortoise are known to be contingent upon thermal conditions. Therefore, it appears that, to a large extent, both electrophysiological and behavioral activity are passive reflections of changes in ambient temperature. It is concluded that the behavior of the tortoise is best characterized as an activity-inactivity cycle. The absence of electrophysiological signs of sleep in the tortoise conforms with the hypothesis that the complete physiological and behavioral manifestations of sleep are unique to homeotherms.

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