M. PALESTINI AND W. LIFSCHITZ 417 



However, one or two days after the completion of sensory deafterentation, 

 the low voltage and fast EEG rhythms reappeared and persisted unmodi- 

 fied through the survival period. 



To sum up, these facts show that the whole desynchronized EEG 

 activity following MPP might be due eitlier to the elimination of some 

 ascending synchronizing influences, and/or to the exaltation of a tonic 

 activity, rostral to the section. The latter would be able to sustain a 

 cortical desynchronization when total deafterentation was done. 



The hypothesis based on a 'synchronizing or possible sleep-inducing 

 influences exerted by a structure present in the caudal brain stem' (Batini, 

 Moruzzi, Palestini, Rossi and Zanchetti, lys-S) has been strongly reinforced 

 by recent experimental data. 



Chronic midpontine hemisections show desynchronization in the hemi- 

 sphere ipsilateral to the section, while the other hemisphere displays both 

 synchronized and desynchronized periods of EEG activity (Cordeau and 

 Mancia, 1959). These results can be explained by the presence of some 

 ascenciing synchronizing influence on the cerebral cortex ipsilateral to the 

 intact pontine region. 



We want to mention another observation here. In an ingenious experi- 

 ment performed in cats, the head circulation was split into two difterent 

 circuits by a ligature of the basilar artery at pontine level, one of the 

 circuits corresponding to the carotid arteries that irrigate the pontine 

 rostral region, midbrain anci cerebrum, and the other to the vertebral 

 arteries for the medulla and the caudal pontine region. In these conditions, 

 intravertebral administration of a low dose of Thiopental produced a 

 general arousal reaction in a previous EEG spontaneously synchronized. 

 These results can be interpreted as a functional and reversible inactivation 

 by the drug of a synchronizing mechanism originating in the lower brain 

 stem (Magni, Moruzzi, Rossi and Zanchetti, 1959). The experiments we 

 have mentioned support the idea of the functional diversity of the reticular 

 formation, to whose well-known desynchronizing influence is now added 

 its synchronizing eftcct upon the cortex. 



C. MIDPONTINE CATS AND WAKING BEHAVIOUR 



The psychophysiological correlation between wakefulness and cortical 

 desynchronization on one side and sleep and synchronization on the other 

 has been recently discussed. Thus, EEG of normal cats during sleep shows 

 periods of desynchronization (Dement, 1958). Observations made on 

 human beings also show this type of EEG during normal sleep (Dement 

 and Kleitman, 1957). 



