STUDIES OF CEREBRAL FUNCTION IN LEARNING 283 



the vicarious functioning of the motor cortex of the opposite side. 

 Kothinann [16] showed that in monkeys the extra-pyramidal paths 

 are able to mediate learned activities. Thus it is certain that what- 

 ever the normal function of the stimulable cortex in higher mammals 

 it is not absolutely necessary for the performance of voluntary acts. 



The chief evidence for the voluntary function of the motor areas 

 comes from the cerebral paralyses in monkeys and man. In them finer 

 manipulative movements are greatly affected and the paralysis is much 

 more severe than in lower mammals, yet even so it is rarely complete. 

 The condition has been characterized as an enormous difficulty rather 

 than an inability to move the paralysed limbs, and there is some 

 evidence that the degree of paralysis varies with the general tonic 

 condition of the organism. 



Thus after cauterization of the stimulable cortex on one side the 

 rhesus monkey may show a well-marked hemiplegia. But if he is 

 badly frightened and chased about the room, he uses the limbs of both 

 sides in an apparently normal manner. Left undisturbed, he again 

 lapses into the paralytic condition. Gierlich [6] summarizes other 

 examples of this sort. Similar incidents are occasionally reported for 

 man. A girl with hemiplegia of fourteen years' standing, following 

 diphtheria, with paralysis of the right limbs and marked contractures, 

 tells me that when her brother pushed her from the wharf into a lake 

 recently she used her paralysed limbs actively in climbing out. This 

 patient is mentally retarded and perhaps not reliable. I know of no 

 well-authenticated case of the sort, but evidence of less pronounced 

 effects of emotional disturbance upon paralyses is frequently encoun- 

 tered. Depressing stimuli, such as discussion of the above patient's 

 very distressing home conditions, increase the extent of contracture 

 and limit the power of voluntary movement. Exciting stimuli, on the 

 other hand, will sometimes increase the extent of voluntary movement, 

 and have been used to advantage in re-education (personal communica- 

 tion from Dr. S. I. Franz). 



All these facts point to the conclusion that, even in primates, it is 

 not so much the mechanism of voluntary movement which is affected in 

 cerebral paralysis, as some facilitating mechanism whose action is usually 

 essential to the movement, yet is not a part of the direct conditioned- 

 reflex arc. Graham Brown's study of facilitation after section of the 

 connections between pre- and post-rolandic areas [3] shows that the 

 descending fibres from both areas act upon the same final common paths, 

 and that transcortical connections are not necessary for the mutual 



