1 84 BRAINS OF RATS AND MEN 



These experiments seem to show that no other spe- 

 cific region of the cortex takes up the visual function 

 vicariously after loss of the visual area. Complete de- 

 cortication has not been successfully done in the rat, 

 so that we do not know whether such an animal can 

 reacquire the brightness-discrimination habit. Judg- 

 ing by what is known of the results of decortication 

 in other species, this would probably be difficult but 

 perhaps not impossible. Lashley says, "data now be- 

 ing accumulated indicate that the destruction of large 

 cerebral areas (more than 60 per cent of the cortex) 

 greatly retards or abolishes the power to form visual 

 habits" (1922, p. 64). And other inconclusive experi- 

 ments lead him to think "that complete destruction 

 of the cortex abolishes a vicarious function which may 

 survive lesser injuries, and that the cortex is the es- 

 sential structure in this vicarious function." 



If in these cases the surviving portion of the cortex 

 (any surviving part, not some specific area) plays 

 some role in the retention of the reacquired habit, it 

 would seem that the process of relearning and reten- 

 tion is not wholly a subcortical matter. But there is 

 no evidence of localization of this aspect of cortical 

 function, and the exact function served by this surviv- 

 ing cortex has not been determined. This is a very in- 

 teresting question to which we must return after ex- 

 amining the additional data on cortical participation 

 in learning. 



Turning now from these brightness-discrimination 



