CEREBEAL FUNCTION IN LEARNING 81 



Group 3. Occipital regions destroyed. In these tests the at- 

 tempt was made to destroy the posterior third of the cortex of 

 both hemispheres. Autopsies showed from 18 to 40 per cent of 

 the cortex destroyed. Accounts of individual experiments follow. 



Number 7. Large female, about 100 days old. The occipital lobes 

 were destroyed by passing a scalpel through two trephine openings about 

 5 mm. in front of the cerebro-cerebellar junction. Recovery was rapid 

 without observable sensory or motor disturbance. Training was be- 

 gun 27 days after the operation. The first three trials were made in 

 very slow time, but thereafter reactions were prompt. Platform a 

 was learned much more quickly than platform b; a marked exception 

 to the usual rule. 



FIG. 3. THE TOTAL EXTENT OF THE LESIONS IN ANIMALS OF GROUP 2 AFTER 

 OPERATIONS ON ONE HEMISPHERE 



Number of trials required for learning 107 



Per cent of total cortex destroyed 32 . 1 



Lesion: Plate I, figure 7. Both occipital regions were completely 

 destroyed above and caudad to the hippocampal lobes, except for a 

 small area on the mesial surface of the left hemisphere at the level of 

 the thalamus. The right hippocampal lobe was degenerated and the 

 external capsules in the occipital lobes of both hemispheres were filled 

 by large cysts. 



Number 8. Large, vigorous male, about 120 days old. The occipi- 

 tal regions were destroyed with a thermo-cautery inserted through 

 two trephine openings situated as in the foregoing case. Recovery 

 was normal. Training was begun 18 days after operation. His reac- 

 tions were prompt from the first: the position of the door was learned 

 by the tenth trial. 



P8YCHOBIOLOGT, VOL. II, NO. 1 



