268 ARCHIVES OF NEUROLOGY AND PSYCHIATRY 



the lesion included the upper half of the operculum. At most, only the lateral 

 facial area escaped destruction. 



Left Hemisphere: The lesion was almost coextensive with that on the right. 

 More of the paracentral gyrus was destroyed and somewhat less of the 

 i iperculum. 



After practically complete destruction of both precentral gyri, this 

 animal gave evidence of perfect retention of visual habits and habits 

 of manipulation. Direct adaptive changes in behavior were made to 

 compensate for weakness of the left arm. 



DISCUSSION OF EXPERIMENTS 



After extensive lesions to the precentral gyri of both hemispheres, 

 each of tbe animals studied gave clear evidence of the retention of 

 patterns of movement which had been acquired before the operative 

 destructions. Evidence of this retention was obtained from a com- 

 parison of the time required for opening the problem boxes in initial 

 training with that for the postoperative retention tests, from the restric- 

 tion of reactions in the postoperative retention tests to the catches of the 

 problem boxes, and from the persistence of individual peculiarities of 

 opening the boxes. 



The average time required by all animals for opening each box in 

 the first five trials of training was 584 43 seconds. An average of only 

 30.7 seconds was required in the first rive trials of the postoperative 

 tests. The animals all failed the hasp box in the preliminary training 

 until first trained without the plug in the staple. In the postoperative 

 tests, they all opened this box promptly with the hasp closed by the 

 plug. At the beginning of the postoperative tests, each animal (except 

 Number 3 with the hasp box) used the same hand or hands for each 

 part of the manipulation as he had before the operation, and attacked 

 the latches in his former manner, although the methods of attack were 

 modified rapidly to compensate for the persistent motor difficulties. All 

 the animals showed perfect retention in the visual discrimination test. 



These results establish conclusively that the cerebral areas destroyed 

 were not essential to the performance of the habits studied, and observa- 

 tions on the general behavior of the animals following recovery from 

 the paralysis justify the further conclusion that the areas are not essen- 

 tial to the performance of any type of complex adaptive or habitual 

 activity. 



Four possible explanations of the results must be considered: 



1. In no case did the operation destroy the entire precentral gyrus 

 of both sides. The parts remaining intact may have contained a suffi- 



-13. This does not include the failures with the has]) box or the times when 

 Number 1 was left in the case over night. 



