CEREBRAL FUNCTION IN THE RAT 131 



the operations upon retention can not be looked upon as the 

 result of a motor insufficiency, nor, probably, as primarily the 

 result of the destruction of the excitable area. 



Previous work (10) on the function of the frontal portion of 

 the cortex in higher mammals (cat and monkey) has given 

 evidence that this part of the cortex is normally utilized in 

 habit-formation, but that in its absence some other portion of 

 the brain may usurp its function. Further, there is evidence 

 that when the habits have been practiced for a long time by 

 normal animals the preservation of the frontal lobes is no longer 

 a condition of their correct functioning; they come to be carried 

 out, probably, at a lower level of nervous organization. It was 

 the primary purpose of this study to determine the amount of 

 practice necessary for retention of a habit after ablation of the 

 part of the cortex originally functional in its performance. This 

 purpose has been largely defeated by the great variation in 

 the extent of destruction in different animals. The results, how- 

 ever, verify for the rat the findings for higher mammals and 

 suggest some additional possibilities of interest. The experi- 

 ments of series I, II, and V indicate either that very simple 

 habits such as that of turning in the simple maze may be ac- 

 quired by normal animals without the utilization of the frontal 

 portion of the cortex at any time during learning, or that the 

 cortex very rapidly ceases to function in the performance of the 

 habit. There is a little evidence, noted in the first paper, that 

 the animals of series I which have been long overtrained retained 

 the habit a little more perfectly than those which were trained 

 to perfect performance. The irregular conditions of training 

 incident to the use of the animals in other experiments and the 

 great variation in the extent of the lesions makes the justice of 

 such a conclusion questionable. 



In the more complex habit of the inclined plane box the presence 

 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. Again, owing to the small number of 

 animals tested and the variation in extent of the lesions the 

 data on the relation of the amount of practice to the functions 



