872 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



mainly to the precentral motor area, and especially 

 to area 6aa in primates [Hassler (82)]. 



As mentioned above, the pallidum is the terminus 

 of an important inflow from the striatum, with fi- 

 bers from the caudate nucleus entering the dorsal 

 third or fourth of the external pallidum, and pro- 

 jections from the putamen entering the ventral two 

 thirds. The pallidal projections from the rostral 

 caudate nucleus are proportionately larger from the 

 expanded head of the nucleus. The putamen appears 

 to exercise control mainly over the anterior part of the 

 nucleus ventralis lateralis (nucleus ventralis oralis 

 anterior, ]'.o.a.) previously discussed, whereas the 

 caudate nucleus projects mainly to thalamic nuclei 

 further rostrally, especially to the nucleus ventralis 

 anterior (nucleus lateropolaris, L.po.}. Although the 

 theory of suppressor areas appears to have been re- 

 futed, it is possible that the strip region of Hines may 

 contain a mechanism inhibiting spinal motor activity. 

 Since Travis (257) has shown that a precentral lesion 

 causes spasticity only if the adjacent supplementary 

 motor area is damaged, a possible explanation of the 

 results of experiments on the strip region may lie in 

 concomitant damage to white matter with interruption 

 of fiber connections to the supplementary motor area 

 on the medial frontal surface. Thalamic projections 

 to this area are uncertain, but may arise in nuclei 

 dorsal to the anterior part of the nucleus ventralis 

 oralis mentioned above. It is suggested that the 

 supplementary motor area would receive mainly in- 

 direct afferents from the caudate nucleus via the 

 rostral pallidum and the nucleus ventralis anterior. 



The neuronal chains of the internal pallidum, the 

 caudal chains influenced by the putamen and the 

 rostral chains controlled b\- the caudate nucleus all 

 represent important afferent pathways to clearly de- 

 fined cortical fields. These cortical fields are major 

 contributors to the pyramidal tract. Thus, this part 

 of the extrapyramidal system i)ecomes an afferent 

 pathway to the pyramidal tract. The striatal system is 

 dependent in turn on cortical fields which utilize the 

 pyramidal tracts as efferent pathways, and in a re- 

 stricted sense the pyramidal tract may be regarded as 

 part of the mechanism of extrapyramidal activities. 



RED NUCLEUS. This nucleus receives its main influx \ia 

 the brachium conjunctivum from the magnocellular 

 part of the dentate nucleus [Hassler {83)]. Since most 

 cerebellar efferent fibers enter or traverse the red 

 nucleus, little is known about which of the deficiency 

 phenomena attributed to the nucleus result from 

 damage to it and which are rather the result of inter- 



ruption of fibers of passage. Fibers from the external 

 pallidum to the red nucleus are described above. 

 Direct \estibular afferents are doubtful. Many authors 

 have described cortical connections, especially from 

 Hines' suppressor strip, but their functional signifi- 

 cance is unknown. 



Two efferent pathways arise in the red nucleus. The 

 rubrospinal tract is composed of large fast-conducting 

 axons of the magnocellular part of the nucleus, but it 

 is poorly developed in primates and very small in man. 

 The central tegmental bundle leaves the dorsomedial 

 red nucleus from the smaller cells of the nucleus and 

 is fully developed only in primates. This bundle [the 

 ventrolateral Teilbiindel of Weisschedel (291)] is con- 

 nected partly with the reticular formation but 

 terminates to a greater extent in the inferior olives. 



NORM.AL .\NU P.\THOLOGIC.\L PHYSIOLOGY OF EXTRA- 

 PYRAMIDAL STRUCTURES: EFFECTS OF STIMUL.'\TION 

 AND ABLATION IN ANIMALS AND OF LESIONS IN MAN 



Up to a few years ago the physiology of the extra- 

 pyramidal motor system was rather sterile. Many 

 clinically established concepts could not be confirmed 

 physiologically. In the following section it therefore 

 appears necessary to discuss not only the results of 

 stimulation and destruction experiments, but also the 

 findings of human pathology. 



Telencephalic Siriutures 



striatum: ANIMAL EXPERIMENTS. The results of stimu- 

 lation and destruction within this highest extrapyrami- 

 dal motor center have long been controversial. In 

 spite of Ferrier's early findings (55) that faradic 

 stimulation of the corpus striatum causes movements 

 with pronounced bending of the head and the whole 

 body to the contralateral side, these and the locomotor 

 movements often observed were usually considered 

 to be the results of stimulation of the internal capsule 

 by escape current loops, particularly since von 

 Bechterew (273) and Rioch & Brenner (218) could 

 not ol^tain them after degeneration of the internal 

 capsule. Wilson (295), on the basis of stereotaxic 

 stimulation with faradic current, even considered the 

 putamen of monkeys as unexcitable. 



The first significant results were obtained with the 

 Hess technique by means of low frequency stimulation 

 of the caudate nucleus in unanesthetized freely mo\ing 

 cats. This procedure produces an apparently purpose- 



