1 82 BRAINS OF RATS AND MEN 



the frontal third of the hemisphere does not interfere 

 with the acquisition of the habit (1920, p. 94; see Fig. 

 42). It is evident that the "motor cortex" and pyram- 

 idal tracts are not essential for the acquisition of 

 this habit. 



Other rats were first trained in the brightness-dis- 

 crimination habit and then various parts of the frontal 



Fig. 43. — ^The total extent of lesions in animals which retained the 

 habit of visual discrimination after operation. Not all of the darkened 

 field was destroyed in any one rat. After Lashley. 



and parietal cortex were removed. The total extent of 

 all of these injuries is shown in Figure 43, but not all 

 of the darkened field was destroyed in any one rat. 

 After the operation some of these animals showed im- 

 pairment of the habit but none of them showed total 

 loss. They all gave unmistakable evidence of some re- 

 tention of the habit. It may be concluded that no spe- 

 cific region of the cortex other than the occipital pole 

 is essential for the preservation of this habit. In a lat- 

 er communication (1922) report is made of a series of 

 experiments directed especially to this problem. The 

 question is this: Is there some specific cortical area 

 outside of the occipital pole which functions vicarious- 



