THE EXTRAPYRAMIDAL MOTOR SYSTEM 



877 



by stimulating the anterior pallidum. However, some 

 of the areas giving this effect are located within the 

 nucleus entopeduncularis. 



Following low-voltage threshold stimulation of the 

 external pallidum with the Hess technique in cats, 

 movements of the contralateral extremities were 

 obtained with violent backward movements of the 

 shoulder combined with rhythmical facial twitches 

 [Hess (106)]. Some of the stimulated points located 

 in the medial entopeduncular nucleus and in the 

 internal capsule produce contraversive turning 

 movements with transition to circling movements 

 [Hassler (89)]. 



pallidum: studies in man. The effects of pallidum 

 stimulation in man have been studied for the first 

 time in the course of stereotaxic operations. These 

 findings have so far been communicated only briefly 

 [Hassler (85, 86, 90)]. Bipolar stimulation of the 

 internal or external pallidum with higher voltages 

 at 20 per sec. produces arousal both in shallow and 

 in deep anesthesia. The patient opens his eyes, tries 

 to orient himself and shows a dilatation of the pupils. 

 In one case of Huntington's chorea the arousal effect 

 following stimulation of the area between external 

 and internal pallidum was so pronounced, in spite of 

 deep general anesthesia, that the patient became 

 reactive to his environment and was able to say a few 

 words; he relapsed into deep anesthesia after the end 

 of the stimulation Repeatedly, stimulation caused 

 respiratory inhibition and e\en arrest, briefly out- 

 lasting the end of the stimulation. During external 

 pallidum stimulation the EEG shows periodical 

 high-\oltage activity which de\elops all over the 

 cerebral cortex in both hemispheres. Only occasionally 

 does it show the desynchronization typical of the 

 electrographic arousal response in animals. Conscious 

 patients, operated upon under local anesthesia, lose 

 contact with their environment during pallidum 

 stimulation and are unable to perform complex 

 movements or to speak accurately. To and fro move- 

 ments, which the patient had previously been in- 

 structed to carry out during stimulation, are dis- 

 continued or markedly slowed and become jerky as 

 long as the stimulation lasts. Low frequency stimu- 

 lation at 4 and 8 per sec. has no definite arousal effect 

 but induces high voltage recruiting responses in the 

 cortex (fig. 18). During stimulation most of the 

 patients consistently showed a tendency (as the head 

 was immobilized) to look to the contralateral side 

 which could l)e overcome however by visual fixation. 

 Some of the patients displayed anxiety and restlessness 



during stimulation of the internal pallidum at higher 

 frequency or at voltages above threshold, described 

 a constricting or hot feeling in the chest and oc- 

 casionally a feeling of vital anxiety in the left chest; 

 some of the patients even screamed anxiously as the 

 stiinulation was repeated. 



When the internal pallidum is stimulated in patients 

 with athetotic, torsion-dystonic or choreiform dis- 

 orders, even single electrical shocks may sometimes 

 trigger a hyperkinetic reaction of prolonged duration. 

 This is not always the case. Stimulation with fre- 

 quencies higher than 8 per sec. regularly activates 

 hyperkinetic reactions if they had disappeared during 

 the operation, or definitely enhances them if they con- 

 tinue during the operation. Even convulsive contrac- 

 tions of the muscles of the neck and of the sterno- 

 cleidomastoid muscle, comparable to spasmodic 

 torticollis, can be produced by pallidum stimulation, 

 but only in patients showing this kind of disorder spon- 

 taneously. The resting tremor in parkinsonian patients 

 can be both enhanced or transitorily blocked by 

 stimulation of the pallidum. Following stimulation at 

 higher frequency it can also be inhibited by synergic 

 flexion of the contralateral arm. 



Riechert, Hassler and Mundinger have also carried 

 out destruction of the internal pallidum in man. In 

 contrast to expectations, this operation, performed 

 unilaterally in more than 180 patients with extra- 

 pyramidal disorders, does not cause parkinsonian 

 symptoms on the contralateral side. Parkinsonism is 

 thus not attributable to a pallidum lesion and is not 

 a pallidum syndrome. The only detectable immediate 

 effect of unilateral destruction of the pallidum in 

 parkinsonism is suppression of the rigidity and reduc- 

 tion of the tremor. During; gradual coagulation of 

 the pallidum (especially of the internal pallidum) in 

 unanesthetized patients it is possible to observe a 

 gradual decrease of muscular rigidity. Tremor may be 

 transitorily enhanced on the contralateral side during 

 high frequency coagulation but is decreased after 

 destruction has taken place. In various hyperkinetic 

 diseases, such as chorea, athetosis and torsion dystonia, 

 hyperkinetic motor activity is also reduced even 

 during the course of the stereota.xic operation, es- 

 pecially by destruction of the internal pallidum. 



Following almost complete unilateral destruction 

 by coagulation of the pallidum, especially of the 

 internal pallidum, yawning, increasing drowsiness, 

 closing of the eyes, impairment of contact with the 

 environment, arrest of spontaneous speaking, sleep 

 or even an acute brief state of disorientation or 

 amentia are ob.served, but later disappear. Transitory 



