THE EXTRAPYRAMIDAL MOTOR SYSTEM 



879 



in restrained animals. Apparently the nucleus has 

 not yet been stimulated in monkeys or human subjects. 



It was interestins; but not understandable without 

 the results obtained by the Hess method that lesions 

 in the same area in cats produce persistent locomotor 

 movements in the horizontal plane (Mella, Waller) 

 which in freely moving cats are directed toward the 

 side of the coagulation. Thus they are mirror images 

 of the stimulation effect. This disorder is a conse- 

 quence of destruction of a tonic (contraversive) 

 turning mechanism in one hemisphere. Rotation of 

 the head alone to the side of stimulation can also be 

 elicited by stimulating in the vicinity of the sub- 

 thalamic nucleus. In these cases the stimulating 

 current reached the ansa mesencephalica ascendens 

 which carries fibers from the nucleus interstitialis 

 [Hassler & Hess (91)] 



In cats destruction of the nucleus subthalamicus 

 together with a part of the surrounding fiber tracts 

 produces nothing but a rhythmic locomotor turning 

 movement to the ipsilateral side as a result of destruc- 

 tion of the tonically active mechanism in this hemi- 

 sphere responsible for contraversive turning, accord- 

 ing to Hassler (89). 



Choreiform movements following lesions in the sub- 

 thalamic nuclei were first observed in lower animals 

 by Lafora (155) and D'Abundo (37). Since 1949 

 Whittier & Mettler (293) have succeeded regularly 

 in producing a 'choreoid hyperkinesia' in the macaque 

 by destruction of the subthalamic nucleus. For this 

 at least 20 per cent of the nucleus must be destroyed 

 without too extensive damage to the neighboring 

 structures. Neither the force nor the duration of the 

 hyperkinesia depends directly upon the percentage of 

 tissue destroyed in the nucleus. A somatotopic or- 

 ganization of the subthalamic nucleus could not be 

 demonstrated [Carpenter & Carpenter (31)]. The 

 hyperkinetic symptoms appear as soon as the subject 

 recovers from anesthesia but reach their maximum 

 2 to 3 days after the operation. They disappear during 

 sleep and in narcosis and may last until death. Usually 

 the contralateral hind leg is involved; less frequently 

 the lower trunk muscles and the anterior limbs also 

 show hyperkinetic movements. The face, neck, 

 pharynx and tongue are not involved with the excep- 

 tion of a random head tremor. In most of the cases the 

 involuntary movements occur in irregular sequences 

 as persisting movements with varying amplitudes and 

 durations (typical choreiform activity). Some of the 

 monkeys show aimless and slow movements of 

 athetoid character, a few a ballistic hyperkinesia 

 characterized by particularly \iolent flinging move- 



ments. During quiet intervals \oluntary movements 

 may initiate the hyperkinetic phenomena, as may 

 emotional stress. In many cases the motor hyper- 

 activity is only intermittently present and normal 

 activity is restored within a few days. In other experi- 

 ments hyperkinesia is combined with a paresis. 



These hyperkineses, chiefly choreiform in nature, 

 are interpreted as a "disorganization of pallidum ac- 

 tivity,' the pallidum receiving afferents from the 

 nucleus subthalamicus. The excess impulses from the 

 pallidum are, according to the authors, conveyed to 

 the midbrain reticular formation or the ventral 

 tegmental area of Tsai through the pallidosubrubral 

 fascicle. 



Relative to stereotaxic therapy, it is important to 

 know that, according to the oi:)servations of Carpenter 

 et al. (33, 34), additional interruption of the lenticular 

 fascicle (H^) or the pallidum will suppress or very 

 markedly decrease choreoid hyperkinesia while 

 simultaneous lesions of the internal capsule do not 

 have the same favorable effect. Hyperkinesia experi- 

 mentally produced in macaques can also be reduced 

 by other procedures: a) bilateral lesions in the lenticu- 

 lar fascicle; b) destruction of more than 8 per cent of 

 the internal pallidum which, however, produces 

 serious disorders (anorexia, somnolence and very 

 much reduced spontaneous motor activity) leading 

 to death within a few days. Normally, unilateral 

 lesions of the internal pallidum do not produce these 

 disorders but still have an excellent effect on the 

 contralateral hyperkinesia. Larger lesions even seem 

 to abolish hyperkinesia completely. Transection of 

 the rubrospinal tract and bilateral destruction of 

 nucleus cuneatus and gracilis had no effect [Orioli 

 & Mettler (205)]. Resection of area 6 contralateral 

 to the experimental hyperkinesia did not reduce 

 hyperkinetic activity. Lesions of the borders of area 4 

 caused both a slight paresis and a decrease in strength 

 of the hyperkinesia. However, if both area 4 and 6 

 were removed, as was done in a rhesus monkey, 

 hyperkinetic activity disappeared on the contralateral 

 side and was replaced by a nonhypertonic paresis 

 [Carpenter & Mettler (32)]. Lesions of the internal 

 capsule in the neighborhood of the subthalamic 

 nucleus do not seem to affect the hyperkinesia, even 

 if they cause pareses. 



NUCLEUS subthalamicus: human studies. Destruction 

 of this nucleus in man is followed by contralateral 

 hemiballism, pro\ided the neighboring structures 

 remain relatively uninjured [Fischer (56), Jakob 

 (129), von Santha (281)]. This, the most violent type 



