Polygraphic and behavioral study of sleep in geese: existence of nuchal atonia during paradoxical sleep.

In adult geese, chronic polygraphic recordings of EEG, EOG, EMG, ECG and respiratory rate completed with behavioral observations allowed the characterization of four states of vigilance: wakefulness (W), drowsiness (D), slow wave sleep (SWS) and paradoxical sleep (PS). The EEG, EOG, EMG general patterns observed during W, D, SWS and PS episodes with nuchal isotonia or hypotonia were similar to those reported in other birds. The characteristic brevity of avian PS was confirmed since this sleep state occupied only 2.8% of the nycthemere in geese. For the first time in an adult bird it was shown that numerous PS episodes were accompanied, as in mammals, by a total disappearance of nuchal EMG activity. These observations made in a bird species with a stable head support when sleeping, suggest that, as in mammals, inhibitory mechanisms leading to a PS related nuchal atonia do exist and that head falling is not the cause of PS episodes brevity in birds.