88o 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



of involuntary motor activity in man, has been 

 described in a previous section (p. 865). In an ex- 

 tensive survey of the hterature Wliittier found lesions 

 to be reported in the contralateral nucleus suij- 

 thalamicus in 40 out of 56 cases of hemiballism which 

 came to necropsy. The remaining 16 cases had lesions 

 mostly in the striatum or pallidum, that is in a struc- 

 ture having a two-way connection with the sub- 

 thalamic nucleus. 



According to experiments in animals and to more 

 recent therapeutic observations in man, liemiballistic 

 symptoms do not necessarily appear even in the 

 presence of severe focalized lesions in the subthalamic 

 nucleus as long as there is serious damage to other 

 neighboring structures, such as the fasciculus lenticu- 

 laris (H:) and thalamicus (Hi), the pedunculus 

 cerebri, the internal capsule or the internal pallidum. 



On the basis of the.se ol)servations, Bucy & Case 

 (24) extensi\ely removed the contralateral arm region 

 in the precentral cortex of a patient with monoballism 

 of an arm and oijtained disappearance of the mo\'e- 

 ments; however, after a year slight insoluntary move- 

 ments reappeared whenever the patient thought hewas 

 observed. Later Meyers el al. (190) severed the white 

 matter between area 4 and area 6aa with a beneficial 

 and permanent effect in a case of hemiballism, as 

 did Walker (285) in another case following transec- 

 tion of the medial two quarters of the pcdunculvis 

 cerebri. 



Bipolar stimulation at 8 per sec. of the oral \entral 

 thalamic nucleus reproduced ballistic hyperkinesia 

 in the contralateral arm which had disappeared 

 during slight anesthesia, according to Hassler, 

 Riechert and Mundinger. Even extensive therapeutic 

 coagulation of the internal pallidum or the oral 

 ventral nuclei did not reliably relieve hemiballism. 

 Therefore lesions were made both in the pallidum 

 and in the medial and posterior parts of the internal 

 capsule close to the p\ramidal tract in a region where 

 bipolar stimulation with a current of very low in- 

 tensity elicited quick twitches in the contralateral 

 facial muscles and in the limbs at the frequency of 

 the stimulus. Contralateral spasms like those of a 

 Jacksonian seizure appeared during coagulation. 

 The very definite decrease or suppression of the 

 ballistic motor activity following the additional 

 coagulation of the efferent pathways of the extra- 

 pyramidal cortical fields seems to be a durable thera- 

 peutic effect. 



The efferent mechanisms of ballistic hyperkinesia 

 are not known at present, as the efferent pathway of 

 the subthalamic nucleus has not vet been definitelv 



located. Since this path is likely to end in the neighbor- 

 hood of the large cells of the nucleus ruijer, release 

 of this system reaching the anterior horn grey via 

 fibers of the rubrospinal tract now .seems probable. 

 In man the large cells of the nucleus ruijer, sending 

 their axons through the rubrospinal tract, appear 

 to convey impulses chiefly to the trunk and the 

 proximal limb muscles. This could explain the onset 

 of the hemiljallistic mo\ements in proximal parts. 

 Furthermore, impulses to the internal pallidum are 

 also suppressed after destruction of the sufjthalamic 

 nucleus, so that the pallidum also can emit uncon- 

 trolled impulses. These impulses are headed for the 

 precentral cortex \ia the anterior ventral oral thalamic 

 nucleus and nucleus lateropolaris of the thalamus. 

 This may account for the more distal components of 

 the athetotic motor disorder in the extremities. Coagu- 

 lation of the internal pallidum and the thalamic 

 nuclei receiving impulses from the pallidum can 

 interrupt these two pathways. However, the effect is 

 more efficient and of longer duration if efferent 

 cortical extrapyramidal or pyramidal systems, es- 

 pecially these coming from area Gaa, 6a/3 and 4s, 

 are interrupted by additional lesion at the capsular 

 or peduncular le\el. The resulting hemiparesis can 

 be very slight. 



In spite of the fact that the effects of lesions of 

 the subthalamic nucleus in man are in good agree- 

 ment with those in animals, it is particularly difficult 

 to define the functional role of the nucleus sub- 

 thalamicus in positi\"e terms. In contrast to numerous 

 observations from human pathology, the experiments 

 of Whittier, Carpenter and Mettler do not indicate 

 that in monkeys there is a somatotopic organization 

 of the nucleus subthalamicus from medial to lateral. 

 On the other hand, there is no doubt about the rather 

 frequent occurrence in man of monoballism of one 

 arm or one leg following a circumscribed lesion in 

 the subthalamic nucleus. 



The subthalamic nucleus seems to have overall 

 control of rhythmic movements of the contralateral 

 limbs, especialh' those for turning around the hori- 

 zontal, longitudinal and trans\erse axes. Bucy (21) 

 considers hemiballism as a release phenomenon follow- 

 ing suppression of cortical inhibitory mechanisms. 

 Whittier & Mettler (293) consider the subthalamic 

 nucleus as comprised of interneurons of the pallidum 

 system. They believe that its destruction is responsible 

 for an o\erall disorganization of the pallidum system 

 which leads to excess motor acti\itv. 



