LOCALIZATION OF LEARNING PROCESS 199 



animals which normally lack cerebral cortex entirely. 

 On the other hand, cortical participation is not ex- 

 cluded when cortex is available. In what fashion the 

 cortex participates, if at all, is of course the problem 

 before us. So far as published observations go there 

 is nothing to indicate that in rats the cortex partici- 

 pates in any way in learning, retention, or recall of the 

 simple maze habit. But we do not know whether the 

 completely decorticated rat with no injury to subcor- 

 tical structures can master or retain this habit. 



The part played by the cortex in habit formation 

 in rats is best revealed by the brightness-discrimina- 

 tion experiments to which reference has already been 

 made (p. 178). In order to clarify the discussion I 

 have ventured a hypothetical schematization of this 

 process as illustrated in Figure 50. The first diagram 

 (I) illustrates the case of the untrained animal. The 

 first presentation of the maze to a hungry rat acts as 

 a stimulus (S) whose "natural" result is exploration 

 of the maze, either in random search for food or per- 

 haps because in previous experience the maze has been 

 associated with feeding. The two alleys F and F^ are 

 ahke. During the course of training (diagram II) food 

 is always presented in an illuminated alley, F, never 

 in a dark alley, 0, so that the simultaneous presence 

 of two stimuli, the maze, 6*, and the light in one alley, 

 S\ is associated with the lighted alley. The neuro- 

 logic connections involved in the thalamus are indi- 

 cated at C. 



