THE EXTRAPYRAMIDAL MOTOR SYSTEM 



9" 



arousal and sleep seems to be particularly evident. 

 However, similar evidence in animals came rather 

 late. Anatomical connections of the extrapyramidal 

 nuclei with the medial thalamus and the reticular 

 formation were known long ago, but their functional 

 significance became evident only when the general 

 importance of the nonspecific thalamoreticular system 

 was recognized after the pioneer work of Hess, of 

 Morison & Dempsey and of Magoun & Moruzzi 



A sleeplike syndrome can be induced by caudate 

 stimulation and pallidal destruction. Early experi- 

 ments of Hess had shown that stimulation not only 

 of the medial thalamus but also of the caudate caused 

 sleep or sleeplike behavior in cats. Later observations 

 of Akert and co-workers (3, 4, 5) in Hess' laboratory 

 have shown that weak repeated stimulation of the 

 caudate by low frequencies causes diminution of 

 motor readiness in cats that can be distinguished from 

 sleep {stridres Inaktivierungssyndrom) (fig. 5, right side). 

 Heath & Hodes (94) have induced sleep by caudate 

 stimulation in monkeys and man. 



Hess has interpreted his and .Akert's stimulation 

 experiments on the caudate as an inhibition of motor 

 mechanisms irradiating to the whole sensorimotor 

 system because proprioceptive correction of posture 

 is also affected, mainly on the contralateral limbs. 

 Hess (107) believes that the caudate nucleus plays a 

 part in the regulation of somatomotor readiness. In 

 contrast to the general diminution of activity and of 

 readiness caused by stimulation of the hypnogenic 

 zone in the medial thalamus, exteroceptive and 

 vegetative mechanisms seem to be less affected by 

 caudate stimulation. In Hess' opinion stimulation of 

 the caudate elicits only a part of the integrated mecha- 

 nism for sleep causing a state similar to the Partial- 

 schlaf observed in man, particularly in some neu- 

 rological disturbances of sleep and muscular tone 

 (narcolepsy and cataplexy). 



Electrophysiological observations of brain poten- 

 tials with implanted electrodes corroborate these 

 findings. Subcortical leads in patients [Knott et al. 

 (151), Meyers et al. (189)] and in monkeys [Hodes et 

 al. (116)] have demonstrated that the earliest elec- 

 trical changes in drowsiness appear in the caudate 

 nucleus. This was true for both natural and bar- 

 biturate-induced sleep. Electrical activity character- 

 istic of sleep (bursts of i to 3 per sec. high voltage 

 waves with occasional 8 to 10 per sec. waves and 

 later 15 to 20 per sec. spindles) occurred earlier in the 

 subcortical structures than in the cortex. Hodes and 

 co-workers discuss the possibility of subcortical driving 

 of the cortex, but they are cautious enough not to 



locate the primary action in any particular nucleus. 

 However, the induction of sleep by stimulation of the 

 caudate by Heath & Hodes and sleeplike behavior by 

 Hess, Akert and co-workers seem to indicate that the 

 caudate is an important center for inactivation of the 

 cortex. The results of electrical stimulation of the 

 caudate in cats, monkeys and men and their bio- 

 electrical effects have been discussed previously in 

 the section on the striatum. 



The effects of pallidotomy in human extrapyram- 

 idal hyperkinesis also indicate a role for the pallidum 

 in sleep regulation, since a constant result following 

 immediately after its extensive destruction is drowsi- 

 ness often progressing to real sleep. (See also the 

 earlier section in this chapter on the pallidum.) 



Further indications of the close coordination be- 

 tween extrapyramidal motor functions and the non- 

 specific reticular system may be seen in the inhibition 

 of vestibular nystagmus during sleep noted by Keser 

 (148) and Jung (134), and the parallel between the 



Fio. 17. .Adynamia after a large coagulation lesion of the 

 posterior hypothalamus. Upper left: Electrical stimulation 

 before coagulation causes raising of head and pupil dilatation. 

 Upper right: After coagulation head and foretrunk are lowered, 

 and muscle tone weakened in the legs. Lower: Coagulation 

 destroys the dynamogenic zone of posterior hypothalamus and 

 the praestitial nucleus. (From Hassler, in Hess" unpublished 

 collection.) 



