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HANDBOOK OF I•H^•SIOLOf;V 



NEUROPHYSIOLOGY II 



'extrapyramidal system' was defined anatomically 

 and, worse still, this anatomical definition was a 

 negative one — the central motor mechanisms ex- 

 cluding only those of the pyramidal tract. Second, our 

 knowledge concerning extrapyramidal functions 

 stems mainly from neurological observations in man. 

 The contribution of animal experiments to this field 

 has Ijeen relatively small. Third, a 'motor system' 

 without sensory control is a fiction, not even a useful 

 fiction. Therefore, sensorimotor integration and 

 dynamic interpretation must be considered here. Thus 

 some overlap with the other chapters on the central 

 organization of motor functions in this work will be 

 inevitable. 



Literally the 'nonpyramidal motor system' would 

 include all motor functions that are not mediated 

 through the pyramidal tract. The anatomical defi- 

 nition as a 'nonpyramidal motor system' leads to the 

 difficulty that, as lower vertebrates have no pyramidal 

 system, evidently their entire motor regulation would 

 of necessity be 'extrapyramidal.' Our subject has to be 

 narrowed down to the physiology of the basal ganglia 

 and some general principles of their motor functions 

 in man and in some laboratory animals. Among the 

 functions of the basal ganglia, only motor eflfects and 

 their afferent control are described. For this reason 

 the contributions of neuroanatomy and clinical 

 neurology have to be considered on an unusually 

 large scale. This may be an excuse for the contribution 

 of two neurologists, one working mainly as a neuro- 

 anatomist (R. H.), the other as a neurophysiologist 

 (R. J.), and for the rather extensive space which 

 neurological details occupy in this chapter. 



In the following we deal only with those basal 

 ganglia conventionally considered part of the so-called 

 extrapyramidal motor system. We will not treat the 

 amygdala and other rhinencephalic parts of the basal 

 ganglia nor the thalamus, except those nuclei con- 

 nected with the striatal system. The nonspecific 

 thalamoreticular system will he only briefly mentioned 

 insofar as auxiliary motor functions in the regulation 

 of sleep, wakefulness and attention are concerned. The 

 lower brain-stem mechanisms related to the vestibular 

 system are treated in other chapters of this work. 



The term 'center' is used in the following approxi- 

 mately in the sense of Winterstein (296) as a structure 

 in the central nervous system without which a certain 

 function cannot be carried out normally and, in the 

 sense of Hess (108), as a device in the central nervous 

 system to establish connections, dependent upon the 

 peripheral milieu situation, the organization of which 

 is directed towards a definite functional result. Centers 



need not always be anatomically circumscribed struc- 

 tures defined as 'nuclei' of the central nervous system. 

 Although we try not to imply that specific motor 

 functions can be 'localized' in certain nuclei, some 

 correlations seem to be well established. Thus in 

 general one may quite safely call the extrapyramidal 

 structures centers for the integration and regulation 

 of motor behavior. 



Dcvelopniint (if Concept of Extrapyramidal Motor System 



With the exception of the cortical extrapyramidal 

 areas and pathways, the concept of the extrapyramidal 

 system has its origin in the findings of human pa- 

 thology. The 'extrapyramidal motor system in the 

 narrow sense' of Spatz {237) corresponds approxi- 

 mately to the 'striatal system' of Vogt & Vogt {266, 

 269) with the exception of the dentate nucleus. 

 Systematic investigation of this system started in 191 1 

 with the observations of Oppenheim & Vogt (204) 

 and Wilson (294), although a particularly con- 

 spicuous disease of the striatal system, the 'status 

 marmoratus,' had already been described by Anton in 

 1896 (7) who proposed that this system be regarded 

 as comprising the structures responsible for choreo- 

 athetotic movements. 



The existence of corticospinal pathways other than 

 the pyramidal tracts was first described in 1895 by 

 Starlinger (245, 246); in 1898 Prus (214) called them 

 'extrapyramidal' on the basis of other findings. These 

 pathways run through the tegmental midbrain and 

 can produce movements following stimulation of the 

 motor cortex even after transection of the pyramids 

 at the medullary level as was ascertained by Roth- 

 mann (222). In numerous experiments Vogt & Vogt 

 (267, 268) then delimited the e.xtrapyramidal motor 

 areas by determining the effects of cortical stimulation 

 before and after isolation of the stimulated areas from 

 the primary motor cortex. 



Attempts to produce symptoms of extrapyramidal 

 diseases by means of lesions have failed until recently. 

 More recent physiological research dealing with the 

 extrapyramidal motor system has been based upon the 

 findings of Hines (113-115) and Fulton (64) and his 

 school concerning the origin of spasticity, as well as 

 the studies of Tower (254-256) concerning the results 

 of 'pure' pyramidal lesions, that is, lesions at the 

 medullary level. Thus it became clear that, contrary 

 to previous concepts, it was erroneous to consider all 

 pyramidal fibers as coming from area 4 gamma and 

 all extrapyramidal motor fibers as originating in the 

 other cortical areas. It was shown that many cortico- 



