Evidence of the duality of the states of sleep

(d) Functional findings

A technique of instrumental and selective deprivation of P.S. (D. Jouvet et al., 1964) was employed in order to dissociate the two states composing behavioural sleep in the adult cat. The animal is placed on a small support floating on water. It can stand or crouch, but the small surface of the support prevents it from Iying down completely and relaxing its muscular tonus without falling into the water. The EEG and EMG activity is recorded continuously or integrated by means of an Oneirograph (M. Jouvet, 1962b). The animal's behaviour is further recorded with the aid of photographs.

Four cats were subjected to successive periods of privation of 10, 24, 36, 48, 72 and 96 h, and 9 and 17 days. A minimum of a week was left between any two sessions to permit complete recuperation.

Results of deprivation:

(i) At the beginning of deprivation, behavioural and EEG arousal was slightly increased (40-60%) as a result of agitation, but phases of slow sleep reappeared within about twelve h. Spindles and even slow waves appeared in the cortex and subcortical structures, while the neck of the animal flexed. These phases of slow sleep were always followed by a sudden arousal caused by loss of balance as the neck bent more and more. Behavioural or EEG P.S. is thus impossible. Whilst deprivation of P.S. is absolute, deprivation of slow sleep is minimal (10-20% depending on the animal). Even during the longest of these periods of deprivation we never observed hallucinatory patterns like those occurring after lesions of the pontine reticular formation which suppress P.S. (M. Jouvet, 1962a). There was a marked increase in the pulse rate.

(ii) Recuperative phases were identical in all the animals. On leaving the tank, even after deprivation for as long as 17 days, the animals always indulged in a stereotyped act of grooming for 30 min to 1 h, after which they fell into a very deep sleep. On awakening their behaviour was reminiscent of asthenia. They were unable to jump onto a chair to obtain food and fell heavily to the ground. The first 6 h of recuperative sleep are represented in Fig. 9: after a deprivation of 72 h a plateau of 60% P.S. (in terms of behavioural sleep) was reached, and was not exceeded even when deprivation lasted for 17 days. This high percentage of P.S. is due to a slight increase in its average duration (8 min against 6 min 20 sec in controls) and especially to the shorter intervals between the phases of P.S. During the first episodes of recuperative P.S. the twitching of the animal's body, paws, tail, and whiskers, was so intense that the animal occasionally presented a picture of epileptic seizures. At these times the arousal threshold is very high and nociceptive stimuli are necessary to awaken the animal, while acoustic stimuli have no effect. The explosive return of P.S. after deprivation thus suggests a phenomenon of rebound and elective recuperation. The relative increase in P.S. during recuperative sleep is proportional to the duration of the deprivation period. It was 20, 60 and 200 h for periods of 2, 5 and 17 days of deprivation respectively. Another important finding was that after deprivation of more than 3 days P.S. can immediately follow the waking state without spindles or slow waves to characterize a transitory phase of slow sleep, as would be the case in the normal animal. Thus total deprivation of P.S. produces a large, lasting and selective increase in P.S. during recuperation. This also speaks in favour of the existence of specific mechanisms for P.S. distinct from those for slow sleep.

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