M. PALESTINI AND W. LIFSCHITZ 419 



In short, the midpoiitinc animal develops a persistent desynchronized 

 EEG, in correlation with seemingly wakeful behaviour. In no case can it 

 be stated that the alert state is higher than the normal, as could be concluded 

 from the EEG pattern. 



Anatomical analysis of the midpontine section shows that it leaves the 

 extreme anterior region of the reticular pontis oralis nucleus intact. This is 

 considered to be one of the areas containing the largest nuniber of cortico- 

 reticular projections (Rossi and Brodal, 1956). The possible participation 

 of these projections in the maintenance of wakefulness, after total de- 

 aft'erentation, needs further experimental demonstration (Batini, Moruzzi, 

 Palcstini, Rossi and Zanchctti, 1959). 



On the other hand, it is suggestive to remember that the lower brain 

 stem, which would exert a synchronizing nifluence, is also the region 

 where the long axon reticular neurones are located. These reticular 

 neurones are connected with thalamic nuclei (Nauta and Kuypers, 1958) 

 from which synchronizing and hypnogenic effects are obtained by electric 

 stimulation. With regard to these anatomo-functional relationships 

 hypothetical consideratitMis have already been made (Batini, Magni, 

 Palestini, Rossi and Zanchetti, 1959; Cordcau and Mancia, 1959). Finally, 

 the possible anatomo-functional interrelations of structures posterior to 

 the midpontine lesion also seem to be interesting. The fact that sleep is 

 followed by a decrease in the muscular tone is well known. Therefore, 

 the origin in the medulla of an ascending synchronizing influence and a 

 descending inhibitory effect on reflex activity is a suggestive fact that 

 needs to be studied. 



D. HABITUATION IN THE MIDPONTINE PREPARATION 



We have already remarked that the pretrigeminal cat is able to follow 

 with vertical eye movements an object passing across its visual field. This 

 is suggestive of the condition of 'purposeful attention' which together 

 with the desynchronized EEG might indicate a possible vigilant state. 

 Eye movements are maintained as long as the object is made to pass to 

 and fro in the visual field, while a normal cat shows a rapid habituation. 



The above observation led us to study habituation in the MPP (Palestini, 

 Lifschitz and Armengol, 1959). Since in this preparation the animal has 

 only two sensory afferences, visual and olfactory, we chose the visual 

 cortex to analyse the behaviour of evoked potentials caused by repetitive 

 stimulation from a flash given at a frequency of i per second. We have 

 considered as habituation the decrease and even disappearance of an evoked 



EE 



