41 6 BRAIN MECHANISMS AND LEARNING 



brain stem, wliosc exclusion would provoke an EEG activation. It is 

 evident also, that the structures rostral to the midpontine lesion are in- 

 dispensable for a desynchronized EEG since a little more rostral pontine 

 transsection to the MPP (rostropontine preparation) produces EEG 

 synchronization. 



B. SENSORY DEAFFERENTATION IN THE MIDPONTINE PRETRIGEMINAL 



PREPARATION 



Bremer (1935) observed that sensory affercnces play an important role 

 in the electric cortical activity of the 'encephale isole' and 'cerveau isolc' 

 animals. Results obtained by Moruzzi and Magoun (1949) permitted a 

 new interpretation of the influences that sensory afterences have upon 

 cortical activity. They would act thrcnigh their activating action on 

 reticular formation. 



Roger, Rossi and Zirondoli (1956) have thrown more light on the same 

 experimental field. They established that the electrical activity of low 

 voltage and high frequency of the 'encephale isolc' is suddenly syn- 

 chronized by the elimination of the trigeminal afterences. 



The results observed in the MPP would seem to be at variance with the 

 above-mentioned facts. Both experimental conditions eliminate the 

 trigeminal afterences but, while Roger ct al. (1956) maintain in their 

 preparation the anatomical continuity of the brain stem, the MPP excludes 

 the ascending influence of the medulla and the caudal pontine region. 



Batini ct al. (1959) repeated and confirmed the results obtained by Roger 

 ct al. (1956). It was thus possible to state that gasserectomy in 'encephale 

 isole' cats determines EEG synchronization. But, if a midpontine trans- 

 section is performed in these animals, the EEG shows the characteristic 

 MPP desynchronization. 



These results permit us to establish another explanation of these facts 

 and to insist, as we shall see later, on a possible ascending synchronizing 

 influence coming from the bulbar reticular formation and from the caudal 

 pontine region. 



The MPP and its characteristic EEG pattern ofters a more satisfactory 

 way of studying the importance of sensory afterences on the electrical 

 activity during wakefulness. Batini, Palestini, Rossi and Zanchetti (1959) 

 eliminated on successive days the olfactory and visual afterences of 

 animals submitted to pretrigeminal section. Destruction o( the olfactory 

 bulbs m the MPP did not modify the EEG. But if these animals suftered a 

 lesion in their optic nerves, their cortical rhythms became synchronized. 



