THE EXTRAPYRAMIDAL MOTOR SYSTEM 



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thalamus [Hassler (8i)] which correspond in part to 

 the hypnogenic zone of Hess (105) and which belong 

 to the ascending reticular system. This forms a non- 

 specific projection system for all major sensory path- 

 ways. Moreover, the external pallidum receives direct 



the thalamus, the lateropolaris {L.po), which has two way 

 connections with the strip region of Hines {.p). The efferent 

 path of area ./j gives collaterals to the caudatum (multineuronal 

 feed-back path) and terminates in the red nucleus (Rii) and the 

 reticular formation (F.rl). The putamen has two (main) 

 efferent pathways, a) One goes to the nucleus niger posterior 

 part (.-V;), where it converges with efferent fibers from the 

 motor corte.x (areas ^7 and 6aa)- From the nucleus niger 

 posterior arises the nigroreticulospinal tract, and from the 

 nucleus niger anterior the efferent fibers seem to go to the 

 pallidum internum from which fibers to the subthalamic nucleus 

 {S.lh) originate. The efferent path from this nucleus reaches 

 the pallidum internum and probably the magnocellular part of 

 the red nucleus (Rii'f or a subrubral region. The efferent fibers 

 of the pallidum externum reach the red nucleus and the reticu- 

 lar formation, b) The other neuronal chain passes through the 

 pallidum internum, the thalamic fascicle to the anterior part 

 of the ventrooral thalamic nucleus (V.o.a.) which has a two- 

 directional connection with area 6aa of the precentral motor 

 cortex. This area 6aa feeds back collaterals which reach the 

 putamen, the direct efferent path reaching the reticular forma- 

 tion and probably the nucleus niger and certainly the spinal 

 cord through the pyramidal tract. 



Pyramidal system. The connections of the large fiber part of the 

 pyramidal tract originate in the parvocellular dentate nucleus 

 (Dt) and reach the posterior ventro-oral nucleus (V.o.p) of the 

 thalamus which has a two-directional connection with area 

 ^y of the precentral motor cortex; this area is the origin of most 

 of the largest fibers of the pyramidal tract which gives collaterals 

 to the putamen and posterior part of the nucleus niger. 



Statokinetic systems. Ascending connections of the vestibular 

 and statokinetic systems arise in the vestibular nuclei (Ve) and 

 as vestibuloreticulothalamic fibers reach the ventrointermediate 

 (V.im) nucleus of the thalamus which has two-directional con- 

 nections with the central region of the cortex, probably with 

 area 3a. This ai'ea influences by efferent fibers the part of the 

 mesencephalic reticular formation which controls all horizontal 

 turning movements to the same side (see fig. 17). Another path, 

 the vestibulomesencephalic tract, runs to the interstitial nucleus 

 (Jst) which coordinates rotating movements. Its efferent path, 

 the interstitiospinal tract, reaches the cervical cord. Ascending 

 fibers go to the inner part or ventro-oral nucleus of thalamus 

 (V.o.i) which is in intimate two-directional connection with the 

 region of area 8, the frontal oculomotor field. Its efferent 

 fibers influence the reticular formation; here a medial part, 

 which controls the anterior gray column by the ventral reticulo- 

 spinal tract, and a lateral part, which operates mainly through 

 the lateral reticulospinal tract, can be distinguished. Whether 

 the efferent mechanism of the nucleus niger is also interrupted 

 in the reticular formation is uncertain. 



Efferent sy.ttems. Efferent mechanisms are the reticulospinal 

 tracts, the rubrospinal tract, the pyramidal tract and the 

 central tegmental tract to the inferior olive (01) which acts as 

 a feed-back mechanism through the cerebellum. 



connections from the medial lemniscus and the 

 spinothalamic tracts [Hassler (81)]. An additional 

 afferent pathway to the pallidum arises in the 

 nucleus interstitialis Hassler (88)]. 



PALLIDOFUGAL PATHS. Pallidothalamocortical and 

 descending pathways to the brain stem form the two 

 major efferent pathways from the external pallidum. 

 The most intimate reciprocal fiber connections exist 

 between the external pallidum, the only equivalent 

 of the pallidum of carnivores, and the subthalamic 

 nucleus of Luys {S.lh.}. There is, moreover, a large 

 afferent inflow to the subthalamic nucleus from the 

 opposite side and from the nucleus interstitialis and 

 praestitialis, but afferents from the brachium con- 

 junctivum are doubtful. The possibility of cortical 

 afferents to the subthalamic nucleus from regions 

 rostral to area 4 is supported by studies of degeneration 

 in human leucotomy material. Many efferent fibers 

 from the subthalamic nucleus return to the pallidum, 

 and particularly to its medial zones [VVhittier & 

 Mettler (293)]. Other efferent fibers descend to the 

 midbrain as the fiber tract Q of Sano, or as the 

 pallidosubrubral tract, and terminate in the midbrain 

 tegmentum caudal to the red nucleus (Ru), according 

 to our own ob.servations in partial agreement with 

 tho.se of Papez, W'hittier and Mettler. This activity 

 probably is con\eyed further caudally by reticulo- 

 spinal pathways and in part by fibers originating in 

 the large-celled caudal portion of the red nucleus and 

 entering the rubrospinal tract, .so inconspicuous in 

 man. 



Fibers from tlie external pallidum also break 

 through the internal capsule and field H2 (fasciculus 

 lenticularis) to terminate in the ventromedial hypo- 

 thalaiTiic nucleus and in the intercalated hypothalamic 

 nucleus. Other fibers from the external pallidum pass 

 in the bundle H2 of Forel to the red nucleus and 

 tegmental fiber systems. 



STRIOPALLIDOCORTICAL SYSTEMS. Many of the iinpulses 

 from the external pallidum are con\'eyed to the 

 internal pallidum. In contrast to older concepts, the 

 latter is not viewed as specifically an effector or motor 

 structure, but rather, by reason of its inajor pro- 

 jections to the thalamus, as an essential link in 

 afferent paths projecting to many cortical areas 

 [Ranson & Ranson (217), Hassler (82)]. Most of its 

 efferent fibers pass in the thalainic fasciculus (Hi of 

 Forel) to terminate in the oral part (V.o.a.) of the 

 nucleus ventralis lateralis of Walker, which projects 



