476 BRAIN MECHANISMS AND LEARNING 



(afferent neuronal habituation). So I considered that this phenomenon was not a 

 good index to objectivate negative learning in other types of preparation, such as 

 decorticated or chronic mesencephalic cats. 



Palestini. I would like to mention experimental data strongly suggesting the 

 presence of a hypnogenic structure in the caudal brain stem. I want to point out also 

 that slides showing the mesencephalic lesions done by Dr Jouvet suggested that 

 the connections with cerebellum and hippocampus are not severed and it is 

 possible that they may be in the brain stem reticular formation. Lastly, the increase 

 in the positive wave has been found in conditioning and also after pre-trcgiminal 

 section in cats. 



Jouvet. If I understood the work of the Moruzzi school, these authors postulate 

 the existence of both a group of tonically ascending excitatory cells in the upper 

 pons and an ascending synchronizing mechanism in the lower pons or behind. 



From our results, it seems that a lower pontine mechanism acts mostly caudally 

 (on the motor outflow) because wc observe a striking absence of EMG activity 

 during the 'paradoxal stage' of sleep. There must be some relationship between the 

 fact activity we observe during this stage of sleep and the rather continuous fast 

 activity shown by the MPP cat. Did someone record at the pontine level in this 

 type of preparation? 



BusER. How long after the decortication did you make your recording and ob- 

 serve the absence of slow waves ; Could there not be any secondary effect (degenera- 

 tion) which actually would be responsible for the disappearance of thalamic slow 

 patterns after decortication. 



Jouvet. There have been some papers about EEC in decorticate animals, mainly 

 those of Morison and Bassett (1945), and Kennard (1943)- These papers were 

 concerned with acute experiments. In sUch conditions these authors could record 

 spindles at the thalamic level immediately after the decortication. In our chronically 

 decorticate cats we could not get any spindles or slow waves when we began to 

 record (usually 6 to 12 hours after the decortication). This fact has been recently 

 confirmed by Sergio and Longo in Rome, working on chronic rabbits. 



In some cats, at the subcortical level, we could record slow waves and spindles 

 during sleep, but a careful anatomical and histological control shows us cortical 

 cells left in place. This fact eliminates, in part, the possibility of some degeneration 

 or hypcrsensitization effects. 



Segundo. The following observations illustrate the participation, as demon- 

 strated by the possibility of either 'habituating' or 'conditioning' the response, of 

 learned issues in the determination of arousal. 



(A) Habituation. Habituation of arousal from sleep was described by Sharpless 

 and Jasper and similar attenuation was shown recently to involve recovery from 

 animal 'hypnosis', a condition that behaviourally and clcctrographically resembles 

 natural sleep (Sharpless and Jasper, 1956; Silva, Esiable and Segundo, I959)- 

 Further studies by Apelbaum and collaborators on EEC 'arousal' habituation have 

 shown that, if a cat was primarily 'habituated' to a 'basic' tone of 200 c.p.s. and 

 then series of other tones (202-500 c.p.s.) were presented, the responsiveness of the 

 animal to the latter was modified in a characteristic manner. Initially, tones close to 

 200 (e.g. 202, 205, 210, 220 c.p.s.) did not induce EEG 'arousal', whereas tones 

 removed from 200 (230-500 c.p.s.) did. As more series were applied to each cat, the 

 remaining tones gradually became inoperant following a succession in which tones 



