THE MOTOR AREAS 643 



Since the excitation in cortical epilepsy spreads to different muscle groups 

 just the same after extirpation of the motor zone on the opposite side from the 

 one stimulated, and since a single group of muscles is not absolved from the effect 

 by extirpation of its own particular field in the cortex when the stimulus is applied 

 to another, it is probable that the actual irradiation takes place through the 

 mediation of subcortical centers. This is borne out also by the fact that once an 

 attack is well advanced extirpation of the motor zone does not stop it. 



F. SUPPRESSION OF THE MOTOR CORTICAL FIELDS 



As the observations given in the preceding chapter have shown, the entire 

 cerebrum can be removed not only from the lower vertebrates but from the 

 rabbit and dog as well, without destroying the ability of the animal to carry 

 out coordinated movements of locomotion. This proves at once that in these 

 animals the motor regions of the cerebral cortex are not indispensable for 

 movements of this kind. However, in the decerebrated dog there were notice- 

 able disturbances in motion, which might not have been caused by removal 

 of the motor region alone but also by the absence of other parts of the cere- 

 brum. In order to establish the physiological importance of the motor areas, 

 it is necessary therefore to study the behavior of animals from which these 

 fields only have been extirpated. 



When the motor fields of one hemisphere have been completely or mainly 

 removed from a dog, for a time immediately following the operation there 

 is a more or less profound disturbance in the movements of the opposite side ; 

 but this effect is only temporary. The animal gradually recovers its ability 

 to move the opposite muscles, and after some time the motor defects become 

 quite minimal. A dog from which Goltz removed the left hemisphere became 

 " silly " ; he was not so lively as before ; did not play with other dogs, etc. 

 But none of his muscles were entirely paralyzed. When he was called he 

 came wagging his tail and let himself be stroked. When one started to go 

 the dog followed. He fought off other dogs that displeased him. He held 

 a piece of bread just as skillfully as a normal dog, but did not hold a bone 

 so well with the opposite foot (the right) as with the other. He could stand 

 up on his hind legs, although the right leg was somewhat weak. He ran 

 here and there of his own accord, but turned oftener to the left than to the 

 right. He could turn to the right, though less skillfully and less quickly. 



It is therefore unquestionably true that a dog which has lost the motor 

 zone of one side can still move those muscles which respond to stimulation 

 of that cortical zone. It has been supposed that such an animal could not 

 perform intentional movements with these muscles. But this view is con- 

 troverted by the following observations on a dog whose entire cerebral cortex 

 on the left side had been removed. 



A bowl was placed before the animal containing bits of meat scattered in 

 some coarse gravel. In scratching for the meat he used his left fore paw. But 

 when this one was held fast he immediately made the same movement with the 

 right fore paw (Goltz). 



In a well-trained dog Gaule trimmed off on both sides all the cortex which 

 could be visibly excited with a weak constant current. After the usual phenom- 

 ena of paralysis had passed off, Gaule trained the dog again and was able to 

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