ROLE OF THE CEREBRAL CORTEX IN THE LEARNING 

 OF AN INSTRUMENTAL CONDITIONAL RESPONSE 



T. Pinto Hamuy 



Because of its complex structure and the degree of development it 

 reaches in the more highly evolved species, the cerebral cortex has been 

 thought in the past to be the seat of all learning. At present, however, 

 there is a tendency to accept that cortical function is not necessarily 

 connected w^ith all levels of learning and that as far as learning processes 

 arc concerned, cortical and subcortical functions are interdependent. 



Pavlov (1942) held that for the learning of a conditioned response (CR) 

 the cerebral cortex is essential. He assumed that the neuronal association 

 between conditioned and unconditioned stimuli developed intracortically. 



Pavlov's assumptions have been challenged by others. Thus, in de- 

 corticated dogs, Zeliony and Kadykov (1938) observed conditioned 

 responses to visual and auditory stimulation. Girden and his associates 

 (1936) in the same preparation obtained conditioning with thermal, 

 tactile and auditory stimuli. 



The results achieved by ablation of specific sensory areas corresponding 

 to the sensory modality of the conditioned stimulus are still more con- 

 clusive. Wing (1947) found it possible in dogs deprived of visual cortex to 

 obtain a CR to a luminous stimulus. Marquis and Hilgard (1937) obtained 

 in monkeys with a similar ablation a conditioned palpebral occlusion to light. 



The evidence quoted above suggests that the integrity of the cerebral 

 cortex is not essential for the acquisition of certain simple types of CR. 

 We assumed that the more flexible the behaviour, the more important 

 becomes the integrity oi the cerebral cortex for its performance. To test 

 this assumption, we decided to study in decorticated rats an instrumental 

 CR (ICR) which, involving an alternative, is an experimental situation oi 

 a higher degree of complexity than that employed by Pavlov. We defined 

 the degree of complexity by the number of alternatives of reaction open to 

 the animal. 



In our experiments, the animals received an electric shock as uncondi- 

 tioned stimulus (US). The animal could avoid it by escaping to another 

 compartment of the chamber (Fig. i). In the classical Pavlovian experi- 

 mental set-up for the establishment of a CR, this stimulus avoidance 

 alternative is not provided. 



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