HOW DO RATS LEARN? 169 



conclusion, "the phylogenetic evidence is not suffi- 

 cient to prove that there has been any speciaHzation 

 of structure to facilitate learning," throws into the 

 discard an enormous mass of evidence, difficult to 

 evaluate, it is true, but in the aggregate very convinc- 

 ing, that the functional activity of the cerebral cortex 

 does facilitate learning, at least of the more complex 

 sorts, even though this holds no monopoly of the 

 capacity for learning. 



3. There is an opinion widely prevalent in psy- 

 chological and pedagogical circles that habits ac- 

 quired by cortical activity when thoroughly automa- 

 tized are short-circuited at subcortical levels. Lashley 

 finds very little actual evidence that this takes place. 

 This opinion "seems to be based chiefly on the desire 

 to hustle unconscious reactions out of the cerebrum 

 and there is no conclusive evidence that any habit 

 which may be performed at subcortical levels was 

 not acquired there in the first place" (1920, p. 65). 



His own experiments strengthen this conviction, 

 for overtraining of rats by more than ten times the 

 number of trials necessary to establish a habit pro- 

 duced no change in the relative parts played by cortex 

 and thalamus in the reaction. A simple brightness- 

 discrimination habit was used in these tests (1921). 

 Normal rats acquire this habit in less than one hun- 

 dred trials. It is totally lost after destruction of the 

 visual cortex in the occipital poles of the hemispheres. 

 After this operation it is reacquired in about the same 



