Sleep patterns in the bird Aratinga canicularis.

Behavioral and electrophysiological features of sleep and wakefulness were studied in chronically implanted adult parakeets, Aratinga canicularis. Four states of vigilance were observed: (1) Wakefulness. It is divided into active and passive. During this state there are generalized motor manifestations which are more frequent and intense in active wakefulness. Cerebral activity is fast and of low amplitude. (2) Drowsiness. Motor activity is notably lower. Blinkings become progressively less frequent. Electroencephalographic patterns are constituted by waves of variable amplitude and frequency. It constitutes 40.7% of the nychthemeral cycle. (3) Slow Wave Sleep (SWS). Animals remain immobile with eyes closed and eye movements are at their lowest frequency. Cerebral activity is slow and of high amplitude. It constitutes 14.7% of the nychthemeral cycle. No sleep spindles are present. (4) Paradoxical sleep (PS). The bird's head tends to drop due to additional muscular relaxation; its eyes remain closed but there are bursts of ocular movements. The EEG is similar to that of wakefulness. This state lasts 7.14 sec on average and occupies 1.98% of the nychthemeral cycle. It is always preceded by SWS. The absence of sleep spindles could be due to the differences in cerebral development compared with mammals.