A QUANTITATIVE STUDY OF ELECTROENCEPHALOGRAPHY, EYE-MOVEMENTS AND NECK ELECTROMYOGRAPHY CHARACTERIZING THE SLEEP-WAKE CYCLE OF THE GUINEA-PIG

The qualitative and quantitative characteristics of cerebral cortex el ectrical activity, ocular motility and muscular activity were studied in six head-restrained guinea-pigs during wakefulness, slow-wave and p aradoxical sleep. Animals were chronically implanted with bipolar elec trodes in the obliquus capitis muscle for electromyographic recordings and epidurally through the parietal bones for electroencephalographic (EEG) recordings. Eye movements were recorded using the scleral searc h-coil technique. After postoperative recovery and a short period of h abituation to immobilization, head-restrained animals exhibited a poly phasic sleep-wake cycle similar to what has already been described in the unrestrained guinea-pig. Paradoxical sleep periods of mean duratio n 110 +/- 42 s occurred at a mean interval of 32.2 +/- 7.2 min. Amplit ude and frequency components of EEG activity were different for each s tate of vigilance. EEG amplitude was highest and frequency range lowes t-with two well-defined peaks at 4 and 10 Hz-during slow-wave sleep. D uring paradoxical sleep, frequencies were higher and amplitudes lower than during wakefulness. Three types of eye movement intermingled with periods of ocular fixation were recorded: saccadic movements during w akefulness and paradoxical sleep, slow drifts during slow-wave sleep a nd paradoxical sleep, and a new type of eye movement-bursts of high-ve locity eye oscillations during paradoxical sleep. Saccadic eye movemen ts during paradoxical sleep were more frequent and showed higher veloc ities and amplitudes than during wakefulness. During paradoxical sleep the episodes of eye oscillation (8-14 Hz) occurred quite regularly ev ery 1.6 s and had a mean duration of 1.4 s. During wakefulness, the ob liquus muscle activity displayed a burst-tonic pattern. Bursting compo nents were closely related to saccadic eye movements directed to the s ide of the recorded muscle. The muscle activity was predominantly toni c during slow-wave sleep and was completely absent during paradoxical sleep except for small bursts or twitches. These twitches were tightly synchronized with the occurrence of the rapid eye movements oriented towards the side of the recorded obliquus muscle, as during wakefulnes s. These results strongly suggest that paradoxical sleep is characteri zed by the oscillatory discharge of at least two neuronal populations: the brainstem saccadic generators and the tecto-reticular spinal netw ork which underlies gaze-orienting behaviour during wakefulness. The o ccurrence of rhythmic discharges at similar to 11 Hz may explain the s pinal motoneurons' inhibition during paradoxical sleep in order to avo id anarchic motor behaviour. Whether these neuronal oscillations are s imply an epiphenomenon or have functional implications remains to be d etermined.