600 BRAIN MECHANISMS AND LEARNING 



In Other words, and in order to draw conclusions concerning the role 

 of the cerebral cortex in the learning of conditioned responses, the follow- 

 ing factors must be taken into consideration: 



I. The kind of CR that is employed, whether a classical Pavlovian or 

 instrumental response. 



3. The nature of the conditioned stimulus. 



3. The type of motor response involved in the experimental situation. 



4. The previous experience of the animal. 



5. The amount of cerebral cortex remaining intact, and 



6. The locus of the lesion. 



In spite of these limitations, some of our results may be considered 

 conclusive in the sense that: ((7) the specific cortex of the CS is essential for 

 the acquisition of this visual habit (posterior group); (h) a lesion of about 

 41 per cent (anterior group) placed outside the specific cortex, may also 

 determine a serious deficit. Nevertheless the 'CS specific cortex' would be 

 more important in the sense that, of two lesions of the same size, the one 

 placed in the visual cortex should cause the greater deficit. 



Neurologically, the learning of an lACR which implies a general 

 motor response, may be regarded as sharing characteristics with both 

 sensory discrimination learning and serial learning. In our experimental 

 situation, as it also occurs in discrihiination learning, the specific cortex is 

 more important than the rest of the cortex; on the other hand, as in maze 

 learning, the participation of other cortical areas is necessary. 



Another important possibility is that the integrity of the cerebral cortex 

 is perhaps essential only for the acquisition of a certain habit and not when 

 preoperative training has taken place. We think that the importance of the 

 cortex in the learning of conditioned reflexes has been minimized because 

 research has been mainly concerned, not with acquisition of a habit, but 

 with postoperative retention and relearning. Another source of mis- 

 interpretations is the tendency to overlook the fact that conditioned 

 responses obtained m decorticated dogs are deeply modified (Girden et al, 

 1936). It seems that, in general, deficits are considered as such only when 

 they appear in their maximal expression. 



GROUP DISCUSSION 



Chow. I wanted to ask Dr Pinto how she interprets her results in the light of 

 Lashley's old study, and his conclusions on the equipotentiality ot the neocortex in 

 the rat. 



Pinto-Hamuy. We have come to an intermediate opinion regarding the impor- 

 tance of the cortex in this kind of learning; we consider its function to some extent 



