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BRAIN MECHANISMS AND LEARNING 



A learning situation of still higher complexity may be obtained through 

 two successive stages of conditioning, as follows: 



I. First stage (electric shock — light): the shock was associated with a 

 luminous stimulus — CS — intended to condition the animal to escape in 

 order to avoid the shock. 



Fig. I 

 Test situation. 



2. Second stage (light — sound) : once the avoidance CR to light was 

 established, the conditioning to sound, by associating it with the light, 

 would be attempted. 



Decorticated rats did not learn to react to the light signal, i.e. they 

 failed to acquire an instrumental avoidance conditional response (lACR) 

 to this stimulus (Pinto-Hamuy, Santibanez, Rojas and Hoffmann, 1957) 

 (Fig. 2). The extent of the decortication in these animals averaged 62 per 

 cent of the total cortex (Fig. 3). 



The failure of these rats to acquire this CR was contrary to the results 

 obtained by other authors, as mentioned (Girden, Mettler, Finch and 

 Culler, T936; Zeliony and Kadykov, 1938). We decided to investigate the 



