270 ARCHIVES OF NEUROLOGY AND PSYCHIATRY 



Nanagas 46 found a few islands of large pyramidal cells in the postcen- 

 tral gyrus, but the great mass of them was restricted to the precentral. 

 Finally, Brown 36 reported that the destruction of the postcentral gyrus 

 did not abolish learning ability or interfere seriously with habits formed 

 before the operation in the chimpanzee. 



4. The only remaining possibility seems to be that the electro- 

 stimulable areas do not include the centrifugal elements of conditioned 

 reflex arcs of any sort. ( It is of course possible that they contain 

 some such elements, but these cannot comprise any significant propor- 

 tion of the total number of centrifugal cells, since their destruction 

 leaves the habits completely unaffected.) In this, the experiments con- 

 firm for primates the results previously reported for the rat. The 

 neural impulses involved in conditioned reactions do not pass from 

 sensory projection areas to the precentral gyrus and thence to lower 

 centers, but must be conducted by centrifugal cells lying outside of the 

 pyramidal system. In the rat. the evidence points to the view that the 

 centrifugal fibers of the sensory projection area itself are primarily 

 involved in this motor function, since the destruction of any fourth of the 

 cerebrum exclusive of the visual areas does not affect the performance 

 of visual habits. 47 Whether or not the same lack of important tran>- 

 cortical conduction holds true for the monkey is questionable in view of 

 the greater proportionate development of the transcortical association 

 tracts in this animal, but it seems established that the "motor areas" are 

 not concerned in the initiation of habitual movements. 



THE CORPUS STRIATUM AND VICARIOUS FUNCTION 



All recent students of the question agree that recovery from cerebral 

 paralysis is not due to the assumption of the function of the destroyed 

 motor cortex by the corresponding area of the opposite side. On the 

 contrary, the simultaneous destruction of the areas in both hemispheres 

 seems to be followed by a rather more rapid recovery than follows the 

 destruction of either alone. The fact has been noted by Grunbaum and 

 Sherrington 20 and by Wagner -\ It was apparent in the slower recov- 

 ery of Number 2 from the first operation than from the second. The 



46. Nanagas, J. C. : Anatomical Studies on the Motor Cortex of Macacus 

 rhesus, J. Comp. Neurol. 35:67-96. 1922. 



47. Experiments now in progress, which indicate that extensive fronto- 

 parieto-temporal lesions may also abolish visual habits without producing 

 a general deterioriation of learning ability, indicate that a mass action of the 

 cerebrum is also somehow involved, but they do not seem to invalidate the con- 

 clusion that the efferent fibers of the sensory projection area are primarilv 

 concerned in the subcortical initiation of movements associated with the receptor 

 for that area. 



