MICHEL JOUVET 475 



that this caudal inhibitory system could be responsible for any negative 

 learning in mesencephalic and ncodccorticated cats. 



(3) Habituation of the arousal reaction and of the orientating reHex 

 necessitates the intervention of an active telcncephalic inliibitory system. 



GROUP DISCUSSION 



Magoun. I wonder if Dr Jouvct's findings resemble those of Hugelin and 

 lionvallct, who have proposed the existence of a negative feedback from the cortex 

 to the lower brain which checks the latter's ficilitating effects upon motor activity. 



They proposed that EEG arousal, evoked by reticulo-cortical stimulation, in- 

 duced a recurrent inhibition of brain stem activity. Can the inability of your 

 decorticate animal to display slow waves in the thalamus in sleep, be attributed to 

 elimination of such corticifugal inhibition ; Have you, or have the group in Pisa, in 

 studies of the slow wave activity of the 'cerveau isole', ever stimulated the cortex to 

 sec whether it is possible to block slow wave activity in the thalamus ? Can reduction 

 of spindle activity in the thalamus of the 'cerveau isole' be used to test the cortici- 

 fugal inhibition oi brain stem activity proposed by Hugelin and Bonvallet? 



JouvET. I am aware of the experiments oi Hugelin and Bonvallet and of their 

 hypothetic negative feed back. But I consider, for the following reasons, that the 

 mechanism which would act during the first stage of sleep is quite different: 



(i) The time course oi these two inhibitory mechanisms is very different. 



In Hugelin and Bonvallet's experiments the inhibitory action of the cortex takes 

 place in a very short time (several milliseconds), hi our chronic experiments, 

 recording directly at the reticular level, we could usually observe the appearance 

 of the slow waves manv minutes after the beginning; ot slow activity at the cortical 

 level. 



(2) But the main objection is this: according to Hugelin and Bonvallet, one 

 may get inhibition ot the reticular formation by stimulation of the reticular 

 formation itself (negative feed back). In our cases, when we stimulated the reticular 

 formation at the beginning or during sleep, we always got arousal, as is well 

 known. If the inhibitory action of the cortex was driven by the reticular formation 

 (as suggested by Hugelin and Bonvallet) we would have expected an augmentation 

 of slow waves. 



I cannot answer you, concerning the stimulation of the cortex in the 'cerveau 

 isole' preparation, because we have not done it. 



Naquet. This winter while doing some experiments on anoxia in the decere- 

 brate cat with Fernandez-Guardiola I found during the recover\' period after 

 anoxia some spindles on the anterior lobe of the cerebellum. 



JouvET. I also recorded on the cerebellum and I found this spindle activity, but 

 with much lower voltage. 



Naquet. Don't you think they come from the cerebellum = 



JouvET. I don't think so, but I have no definite proof up to now. 



Naquet. Have you tried to explore the habituation for click stimuli in the 

 cochlear nucleus in your mesencephalic cat? 



JouvET. I could never obtain, even in a series of intact animals, a consistent decrease 

 of acoustic evoked potentials at the cochlear nucleus level bv repetition of clicks 



