598 



BRAIN MECHANISMS AND LEARNING 



flicker response. Girden ct al. (1936) were able to install ni a decorticated 

 dog, CRs to thermal, auditory and tactile stimuli, but were unable to do 

 so with light. 



It is possible that the easier establishment of CRs to auditory stimuli in 

 comparison with light signals is related to the fact reported by Bernhaut 

 er ^/. (1953) that auditory stimuh are in general more effective activators of 

 the reticular formation and thus of the cortical projection areas. On the 

 other hand, the assumed facihtatory activity of the cortex would be more 

 essential for the establishment of a visual memory trace on sub-cortical 

 structures. 



NORMAL RATS 



uj 100 



to 80 



o 40 



N = I5 



A visuol codifioned reflex 

 o auditory conditioned reflex 



-T — I — I — I — r— 



5 10 15 20 



TEN TRIAL UNITS 



25 



Fig. 8 

 Learning curves of one ACR and a VCR in two groups of 

 normal rats. 



The Study of other possible variables depending on the experimental 

 situation are under way. 



(f) Another point investigated was the influence of preoperative training 

 on the capacity of decorticated rats to acquire a VCR. 



Seven animals were trained in this avoidance CR before decortication. 

 Decortication determined a loss of the habit, which could be, however, 

 relearned up to a certain level (Fig. 9). They scored a level of 70 per cent of 

 CR at the twenty-fourth session, which normal rats had already reached 

 at the tenth. 



We were also interested in finding out the degree of specifity that this 

 previous experience required: that is, if the training in the pre-operative 

 period should be conducted with the same CS used post-operatively. With 

 this idea in mind, we trained eight animals to respond to an auditory 



