Discussion

Moruzzi : I should like to report some experiments which have been performed in Genoa by G. F. Rossi and his colleagues, T. Hara, E. Favale and G. Sacco. These experiments also concern the stage of sleep which is characterized, in the cat, by a flat EEG record. Hara, Favale, Rossi and Sacco (1960. Boll. Soc. Ital. Biol. sper., 36, 1203) have fully confirmed the observation by Jouvet, Michel and Courjon that the electromyogram of neck muscles is silent during this stage of sleep. They have also confirmed that the reticular responses to clicks are greatly decreased and even abolished, and that the threshold for behavioural arousal elicited by reticular stimulation is much higher. Hence they agree with the view that the sleep is deeper in these stages than when high voltage slow waves are present on the EEG record. The following observations, however, point out that there are also striking electrophysiological similarities with the conditions occurring during wakefulness: (1) the recruiting responses are abolished or strongly decreased; (2) the EEG synchronization elicited by low-rate stimulation of the brain stem reticular formation is also abolished; finally (3) an intravenous injection of thiopentone sodium (10-20 mg./kg.) will synchronize the EEG, while the electromyogram of neck muscles remains silent and the threshold for behavioural arousal is further increased. The same EEG synchronization occurs when barbiturates are injected on the background of low voltage fast activity that characterizes the pretrigeminal midpontine preparation (Batini, C., Moruzzi, G., Palestini, M., Rossi, G. F., and Zanchetti, A. [1959]. Arch. Ital. Biol., 97, 1). Dr. Jouvet, can you suggest an explanation for the effect of thiopentone sodium during the deep stage of sleep characterized by a flat EEG record ?

Jouvet : Sometimes during the paradoxical phase if you make a noise the cat will not wake up but will get to the slow wave stage of sleep (i.e. it will go back to a lighter stage of sleep).

Moruzzi : The doses of thiopentone sodium used by Rossi and his colleagues would produce typical spindles, when injected in an awake cat. When injected during deep sleep they still have a depressant influence, as shown by behavioural tests. Moreover the EMG of the neck muscles remains silent. It is puzzling that the EEG reverts to patterns that are regarded as typical of lighter stages of sleep following injection of thiopentone sodium.

Jouvet : But this is narcosis and not sleep

Bradley : You mentioned using atropine and eserine, Dr. Jouvet. It would be interesting to know what their effects are. I would suspect that they modify the electrical record without altering the behavioural pattern.

Jouvet : Yes, under atropine there is no fast activity during sleep and also there is no total disappearance of EMG activity, so that it looks as though atropine would block this mechanism, and that this mechanism is somewhat cholinergic in nature. With eserine the duration of the paradoxical stage of sleep is much longer but the periodicity remains the same. There was no behavioural change in sleep with atropine but with eserine the eye movements were very much more enhanced.

Bremer : I have very great appreciation of your work, Dr. Jouvet, and the only reservation I should like to make is: are we compelled to admit that this flat desynchronized tracing necessarily means a great activation of the cortex ? Could we not assume that the tracing is flat for other reasons but that it is not the same flattening as in arousal ? In the figure published by W. Dement (I958. Electroenceph. Clin. Neurophysiol., 10, 291) there is a distinct difference between the awakening tracing and the "activated sleep" one. Therefore it would be a relief if we could decide that the so-called paradoxical or activated sleep is not activation of the cortex, which would be a really paradoxical affair.

Jouvet : From the EEG record it is not possible to decide whether the cat is awake or in deep sleep. You are obliged to look at the EMG activity.

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