M. PALESTINI AND W. LIFSCHITZ 4I5 



The EEG observations at hourly intervals for no less than 24 consecutive 

 hours showed that cats suffering midpontine lesions present a desyn- 

 chronized activity significantly more persistent than normal animals. 



Such an experimental hnding makes it necessary to verify some variables 

 and only thus can an hypothesis about the probable mechanism underlying 

 this lasting electrocortical dcsynchronization be postulated. 



In fact, the desychronizcd EEG in the MPP could be due to an irritative 

 action, while the low voltage pattern could be the result of a depressed 

 cortical activity. Different controls effected in the animals during the post- 

 operative survival time (1-9 days) made the first possibility unlikely while 

 the second one was completely dismissed (Batiiii, Moruzzi, Palestini, 

 Rossi anci Zanchetti, 1959). 



Some humoral factors arc known to play a role in EEG activation. For 

 instance, the eiicct of adrenaline on the cortical arousal is widely known. 

 Nevertheless, it must be noted that adrenaline does not act directly on the 

 cerebral cortex, but through the reticular formation. Its desynchronizing 

 efiect is not disclosed in the 'cerveau isolc' but is found in transsections 

 similar to the midpontine (Bonvallet, Dell, Hiebel, 1953). On the other 

 hand, there is some evidence of increased adrenaline secretion in decere- 

 brated animals (Anderson, Bates, Hawthorne, Haymaker, Knowlton, 

 Riosch, Spence, Wilson, 1957) which drops below normal levels in the 

 spinal dogs. The above circumstances made it necessary to establish the 

 role of adrenaline 111 the EEG activation of the MPP (Batini, Magni, 

 Palestini, Rossi and Zanchetti, 1959). 



Midpontine cats were observed for 24 hours following which a section 

 at Cj was performed in order to eliminate any brain stem influence on the 

 adrenal gland. In these cases, the EEG remained desynchronized (Batini, 

 Magni, Palestini, Rossi and Zanchetti, 1959). 



The COo blood increase must not be neglected either especially since 

 the MPP sometimes presents periodic breathing. In a group of cats, the 

 gaseous composition of the arterial blood was measured before and after 

 the midpontine operation. This experiment demonstrated that the EEG 

 activating pattern in the MPP does not depend on blood CO.^ pressure 

 changes. 



Summing up, the authors of these experiments stated: 'Irritative 

 phenomena or humoral factors may occasionally contribute to, but are 

 not likely to be responsible for the EEG activation' (Batini, Magni, 

 Palestini, Rossi and Zanchetti, 1959). 



All these experimental results support the hypothesis of a possible 

 synchronizing structure, placed behind the midpontine section in the 



