MECHANISMS OF LEARNING 187 



more complex habit of the inclined plane box the pres- 

 ence of some portion of the frontal pole is evidently 

 a condition for the performance of the habit where 

 this has been acquired with the frontal pole intact'* 



(P- 131)- 



If the frontal poles were almost completely de- 

 troyed the habit was impaired but not totally lost. In 

 some cases of total loss of the habit it was reacquired 

 more or less perfectly after additional training; in 

 other cases it was not relearned, these probably in all 

 instances having injuries to the corpus striatum in ad- 

 dition to the cortex. 



In these experiments, as in those on the brightness- 

 discrimination habit, we have clear evidence of corti- 

 cal participation in the retention of the habit acquired 

 by a normal animal. In the one case, the occipital cor- 

 tex is necessary; in the other case, the frontal pole. In 

 both cases, only a small part of the specific cortex is 

 necessary and that need not always be the same part. 

 In both cases, the habit may be learned by an animal 

 from which any third of the cortex has been removed 

 as readily as by normal rats. No particular part of the 

 cortex is essential for learning, though the preserva- 

 tion of some cortex in a special region may be neces- 

 sary for the preservation of a habit previously learned 

 while the cortex was intact. Before further considera- 

 tion of the significance of this very interesting situa- 

 tion, attention should be called to some further ex- 

 periments upon problem-box learning. 



