552 



BRAIN MECHANISMS AND LEARNING 



(CRs) ill dogs, and our results are in many respects similar to those obtained by Dr 

 Buser, it would be relevant to summarize them at this point. 



The general method of our experiments was such, that we trained the animals to 

 perform a motor act consisting in lifting the right foreleg and putting it on the 

 food-tray to given conditioned stimuli (CSs); each such movement pertormed to a 

 CS was reinforced by food. After the motor CR was firmly established, particular 

 parts of the scnsori-motor cortex, or the whole of it, were removed and the effects 

 of these lesions examined. I shall speak here only on the results of bilateral ablations. 



Fig. I 

 The dorsal and lateral surface of the cerebral cortex of dog represented on the plan. 

 I, sensory cortex; II, motor cortex; III, pre-motor cortex, a, sulcus ansatus; c, sulcus 

 centralis; cr, sulcus cruciatus; pr, sulcus prcsylvius. 



\n the course of our study it appeared to be useful to divide the scnsori-motor 

 cortex into three roughly parallel belts (Fig. i): i. 'sensory cortex', situated be- 

 tween the line of sulcus ansatus and of sulcus centralis and corresponding to the 

 zone described recently by Hamuy, Broniiley and Woolsey; 2. 'motor cortex', 

 situated between the line of sulcus centralis and of sulcus cruciatus; 3. 'premotor 

 cortex', situated between sulcus cruciatus and its prolongation and sulcus pres)'lvius. 



After ablation of the first strip — sensory area — the instrumental CR is lost for 

 several weeks, but the general behaviour of the animal is quite adequate, and he 

 reacts correctly to CSs, although he seems unable to perform the trained movement. 

 After some time the instrumental reaction returns without additional training 

 (Stepieii and Stepieii, 1959). 



