CEREBRAL FUNCTION IN THE RAT 101 



the fact that he was too weak to jump the full distance readily 

 and usually jumped from near the side of the restraining cage, 

 catching its wires if he fell short. In the repeated failures to 

 open the door by jumping up at this place a new method of 

 working the plane was gradually evolved; he came to scramble 

 up over the lower end of the plane, turn and push down on its 

 free end until the door opened. 



The average time per trial for the first five trials of the re- 

 tention tests was: to plane, 176 seconds; to door, 13 seconds. 

 The relations of the practice curves of learning and retention 

 are practically the same as for those shown in experiments 20, 

 21, and 22. 



Lesion (plate III, fig. 23). Right hemisphere. There is a 

 transverse incision extending cephalad from above the hippo- 

 campus through the lateral ventricle and caudal end of the 

 corpus striatum to the peduncle. The internal capsule and the 

 fibers of the peduncle are uninjured, so that the lesion probably 

 involves little more than the superficial areas through which the 

 knife passed. This includes the greater part of the cortex above 

 the corpus callosum and a narrower band extending down over 

 the orbital surface. 



Left hemisphere. There is a transverse lesion extending 

 from above the anterior border of the hippocampus to the base 

 of the olfactory lobe, transecting the corpus striatum and 

 completely severing the portion of the cortex lying cephalad 

 to it. 



Destruction of all of the left frontal region and the temporal 

 region of the right was followed by the retention of the stereotyped 

 mode of reacting to the problem box but with inaccuracies of ad- 

 justment which resulted in the acquirement of a new mode of 

 response. 



Experiment 24. The frontal poles of both hemispheres of a 

 medium sized female rat, 147 days old, were incised through 

 large trephine holes, well back of the fronto-parietal suture. 

 She had been trained previously for 75 trials on the inclined- 

 plane box. The average time per trial required for the first 

 five trials of training was: to plane, 2422 seconds; to door, 23 



