CEREBRAL FUNCTION IN THE RAT 105 



Frontal pole destroyed: animals in which the habit was lost but 

 reacquired after operation 



Experiment 27. The frontal poles of the cortex were incised 

 in a small female rat, 145 days old, through two trephine holes 

 at the frontal-parietal suture. The animal had been given 30 

 trials on the inclined-plane box. The average time required for 

 the first five trials was: to plane, 396 seconds; to door, 23 sec- 

 onds. The average time per trial for the last five trials was: 

 to plane, 24 seconds; to door, 4.0 seconds. The animal was 

 very weak from the operation and could not be tested for eight 

 days. On the ninth and tenth days she was very spastic and 

 remained motionless in the restraining cage. On the eleventh 

 day she first tripped the catch and on the following days im- 

 proved considerably in the directness of her approach to the 

 plane but never reached her previous efficiency. Throughout 

 the period of retraining she remained spastic and lost weight 

 rapidly. During the first trials of retraining there was ne,ver 

 any indication of the retention of any specific mode of reacting 

 to the problem box. The average time per trial for the first 

 five trials of the retention tests was: to plane, 599 seconds; to 

 door, 65 seconds. 



Lesion (plate III, fig. 27). Right hemisphere. There is a 

 transverse section passing over the anterior face of the gyrus 

 hippocampus, through the lateral ventricle to the base of the 

 hemisphere, separating all parts of the cortex in front of the an- 

 terior horn of the lateral ventricle. The corpus striatum is 

 completely destroyed and the lesion extends caudad from it 

 along the external capsule to the hippocampus, with degenera- 

 tion of all the cortex laterad to it. 



Left hemisphere. The lesion is less extensive, passing ven- 

 trad just behind the knee of the corpus callosum to the base of 

 the olfactory bulb and out diagonally through the anterior end 

 of the corpus striatum to the cortex, severing the anterior pole. 



The destruction of the anterior poles of both hemispheres, of 

 part of the orbital surface of one hemisphere, and of all of one and 

 part of the other corpus striatum was followed by a persistent spas- 



