MICHEL JOUVET 473 



cortical activity has already been found in cats and human beings (Demcnt- 

 Kleitnian) and some arguments suggest that it could reflect a dream 

 activity. 



Since negative learning is concerned with the occurrence of sleep, its 

 aspects (habituation of the arousal in sleeping cats, and habituation of the 

 orientation reflex in awake cats) were studied in relation to the telen- 

 cephalic inhibitory slow waves (stage i) and the rhombencephalic spindle 

 activity (stage 2). 



II. THE HABITUATION OF THE AROUSAL 



Repetition of a specific tone which initially produces long lasting 

 arousal of a sleeping cat, fails to do so after several trials. A study of the 

 effects of variations of the stimulus and of the effects of total neodecortica- 

 tion and transscction of the brain stem upon this habituation phenomenon 

 has led to the following conclusions (Fig. 9) : 



(1) Habituation of the arousal docs not depend on changes (i.e. 'block- 

 age', 'inhibition') occurring in the specific auditory pathways or m the 

 non-specific ascending pathways (mesencephalic reticular formation) 

 since cochlear, reticular (Fig. 11) and cortical auditory potentials (Fig. 8) 

 of great amplitude were recorded during complete habituation of the 

 arousal. 



(2) Habituation of the arousal does not depend on some intrinsic 

 inhibitory reticular mechanism since it is not possible to obtain habituation 

 of arousal (as judged on the arousal from stage 2 of sleep) in chronic 

 mesencephalic or neodecorticated cats (Fig. 12). 



(3) Habituation of the arousal may be obtained in cats with subtotal 

 transscction of the brain stem cir in subtotally decorticated cats. The 

 smaller the cortical surface left intact, the longer is the process of habitua- 

 tion (Fig. 10). 



(4) These results suggest that the habituation of the arousal reaction 

 depends on the entry in action of a rostral inhibitory system (in which the 

 neocortex is an essential relay) which acts downwards upon the ascending 

 activating system. 



III. HABITUATION OF THE ORIENTATING REFLEX 



Novel indifferent stimuli (light and intermittent tone) evoke an orienta- 

 ting reflex in an awake cat. They rapidly tailed to do so if repeated 

 (habituation of the orientating reflex). If these stimuli were repeated still 

 further, a stage of behavioural sleep may be obtained (Pavlovian internal 

 inhibition). 



