CEREBRAL FUNCTION IN LEARNING 107 



Lesion: Plate III, figure 6. The dorsal convexity of both frontal 

 poles was completely destroyed. 



Both these animals gave certain evidence of discrimination 

 within 24 hours after the operation. In both the frontal pole 

 was completely destroyed. They had not been overtrained, so 

 that there is no reason to believe that a once cortical habit had 

 been reduced by practice to lower levels. It is probable that the 

 frontal pole of the cerebrum is not functional either in the forma- 

 tion or the retention of the habit of visual discrimination. 



Group 2. Parietal regions destroyed. 



Number 7. Small male, 130 days old. Trained in brightness 

 discrimination. Was always erratic and given to exploration. 



Number of trials required for learning 220 



Preliminary retention tests, per cent error 7.5 



The parietal areas of both hemispheres were injured by incision through 

 two trephine holes extending backward from the fronto-parietal suture. 

 Retention was tested on the following day. He was then excited and 

 restless, his reactions were quick, but showed an exploratory character, 

 an exaggeration of his previous behavior. On the second day he was 

 stuporous and was not tested. On the third and later days he made 

 no error and gave secondary evidence of perfect discrimination. 



Postoperative retention tests, per cent error 



(After first day) 



Lesion: Plate III, figure 7. The central portion of the convexity 

 of both hemispheres was replaced by cysts. The degenerated cortex 

 extended from the knee of the corpus callosum caudad to the anterior 

 margin of the hippocampus, laterad from the longitudinal sinus to 

 the orbital surfaces. 



Number 8. Small male (castrated), 115 days old. Trained in 

 brightness discrimination. 



Number of trials required for learning 60 



Preliminary retention tests, per cent error 2.5 



Operation was as in the case of number 7. Retention was tested on 

 the day following operation. For several days after operation the rat's 



