Part I : Experimental results obtained on cats

The rhombencephalic phase of sleep Results

V. Ontogenesis of the RPS

The study of sleep in kittens (Jouvet et al. 1961b) shows that RPS is the first pattern of sleep observed after birth and confirms the duality of the neural structures responsible for the fast cortical activity during RPS and arousal. Indeed, during the first week after birth, behavioral RPS with total disappearance of the EMG of the neck, rapid eye movements, acceleration and irregularity of respiration and decrease of the heart rate appears during approximately 40 per cent of the record and represents almost the totality of behavioral sleep. At this time, there is no alteration of the cortical activity which remains the same whatever may be the state of wakefulness (very low voltage flat EEG with some regular 12-15/sec spindling activity; see Fig. 12).

Around the end of the second week, low voltage fast EEG activity appears during the RPS. However, at this stage the cortical activity remains slow (6-8/sec) during arousal and some short periods of slow EEG sleep (without EMG activity but also without rapid eye movements) begin to appear.

During the 3rd week only, tonic cortical arousal appears, almost at the same time that a typical slow phase of sleep (with EMG activity) begins to be recorded.

At the end of the 2nd month, the EEG activity of the kitten is similar to the adult cat with its three classical patterns: arousal, SPS with EMG activity and RPS.

Thus, during maturation and the progression of synaptic neuronal and glial organization of the cortex, the cortical EEG activity is modified at first by the ponto limbic system during the periodical RPS and secondly only by the reticular activating system whereas a phase of slow sleep without EMG activity, which is very exceptional in the adult cat, develops before giving way to the telencephalic phase of sleep ( Fig. 13).

The assembling of these results permits us to conclude that RPS depends on the periodical activity of a system whose structural organization may be summarized as follows: the integrity of a neuronal pool situated at the level of the nucleus reticularis pontis caudalis is necessary for the periodical appearance of RPS. This "center" is connected with the cortex through ascending pathways different from the reticular activating system. These pathways, going through the ventral mesencephalon, the subthalamic region, probably at the level of the midbrain limbic circuit, are specially connected with the limbic system. The descending pathways, coming from the nucleus reticularis pontis caudalis and responsible for the behavioral aspects of RPS, are probably related with the ponto-bulbar inhibitory reticular formation. The mechanisms of the physiological triggering of RPS are still unknown, but some results suggest that this phase depends upon a neurohumoral mechanism.

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