CEREBRAL FUNCTION IN THE RAT 95 



During the first days of the retention tests she frequently 

 leaped into the air, whirled through 180 degrees, and snapped 

 her jaws repeatedly, or at other times spun about in a similar 

 manner and bit her own tail. Another movement which oc- 

 curred frequently was a sort of scampering, a series of short 

 leaps which did not carry her forward more than a few 

 inches. These movements, as well as the inexactness of the 

 reactions to the plane served to prolong the time and make 

 it less comparable with the time of learning. Training was 

 continued for 45 trials after the operation. The average time 

 for the first five trials of the retention tests was: to plane, 63 

 seconds; to door, 23 seconds. The rate of improvement was 

 more uniform and at first more rapid than that observed during 

 learning, but the time required for springing the catch was not 

 reduced so low as it had been before the operation. The rate of 

 learning and of improvement in the retention tests are shown in 

 figure 8, where the total time required for successive groups of 

 five trials is plotted. 



Lesions (plate III, fig. 20). Right hemisphere. There is a 

 transverse lesion on the anterior covexity, passing forward along 

 the fibers of the callosum and through the end of the forceps of 

 the callosum to the base of the olfactory bulb, completely sep- 

 arating the frontal pole. 



Left hemisphere. The lesion is quite similar to that on the 

 right but does not extend quite to the olfactory bulb and pre- 

 serves the greater part of the mesial face of the frontal pole. 



After nearly complete destruction of the frontal poles of both 

 hemispheres this rat retained her previous method of tripping the 

 catch. There ivas, however, some inaccuracy of movement indicat- 

 ing a partial loss of the habit. 



Experiment 21. The frontal pole of the cortex was destroyed 

 in a small female, 130 days old. She had been trained for 40 

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

 the first five trials was: to plane, 618 seconds; to door, 74 sec- 

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

 to plane, 5.2 seconds; to door, 1.8 seconds. 



Retention was first tested on the day following the operation. 



