200 BRAIN MECHANISMS AND LEARNING 



This point of view undoubtedly fnids justification in the facihtating 

 effect which develops in the cortical cells for the excitations coming to the 

 cortex along the specific lemniscus system. This conclusion is also favoured 

 by the phenomenon of 'awakening' or desynchronization of the 

 cortical electrical activity which is always of a generalized nature and 

 seems to be independent oi the biological quality of the unfolding 

 reactions. 



However, along with these remarkable generalizations, our laboratory 

 has obtained tacts attesting that the non-specific activating effect of the 

 brain stem reticular formation on the cerebral cortex is or<^iviical]y connected 

 with the hioh\i^ical specificity of the (^ii'en conditioned reaction. It proved 

 possible to block by means of chlorpromazinc (amuiasinc) the activating 

 effect of the reticular formation for the conditioned defensive reaction, at 

 the same time retaining the activating effect on the cortex for the alinien- 

 tary reaction, i.e. for a reaction of another biological quality. At this 

 moment the animal can greedily eat the food offered to it (Gavlichck, 

 1958) (Fig. 5). 



Similarly blocking the defensive activation of cortical electrical activity 

 by chlorpromazinc fails to eliminate the animal's waking state which, as is 

 well known, is also maintained by the activating effect of the brain stem 

 reticular formation on the cerebral cortex (Fig. 6). 



Thus it was demonstrated beyond all doubt that there arc several 

 activating influences on the cerebral cortex and that each of theni may he 

 hhuked indii'idnally because of the different chemical specificity of the nerrous 

 substrate on iidiich each of these bioh-x^ically different reactions occur. 



What is the significance of this varying biological specificity of the 

 activating influences on the cerebral cortex occurring during the afferent 

 synthesis which precedes the formation of the conditioned reaction itself ■ 



In the first place it contributes to the sek-ctii'e rise in the excitability 

 ('facihtation') of the neural elements in the cerebral cortex, which in the 

 given animal were historically associated, by the principle of conditioned 

 coupling, with the inborn subcortical reaction of the given biological 

 quality (positive or negative). 



Owing to this selective involvement of the cortical elements the 

 mobilization of the numerous cortical systemic connections, which help 

 to complete the stage of afferent synthesis, proceeds much faster and more 

 efficiently. 



Our view of the specific, i.e. selective, activating influence of the 

 reticular formation on the cerebral cortex with the perceptibk oeiieralized 

 desynchronization of its eh'cfrical activity fits in with the remarkable experi- 



