SENSORIMOTOR CORTICAL ACTIVITIES 



815 



cortex results in a small but definite impairment in 

 this function in man. However, the essential participa- 

 tion of motor mechanisms cannot be excluded by 

 these studies. It would appear that any motor deficit 

 would interfere with the performance of the essential 

 observations necessary to such an anaylsis. 



Efferent fibers from the cortex duplicate the thala- 

 mocortical ones in many areas and terminate largely, 

 but not exclusively, in the same thalamic nuclei (364, 

 447; cf. 240, 353). Physiological data (125, 133, 342, 

 346), as well as recent anatomical studies concerning 

 areas 4 and 6 (240) and the parietal lobe (cf. 239, 

 353), are available. Numerous investigators have 

 advanced hypotheses concerning the functional role 

 of these fibers, called by Ramon y Cajal (371) 'de 

 I'attention expectante.' Reference should be made to 

 the work of Peele (353) in which these ideas are 

 reviewed. They tend to attribute to these fibers a 

 role in the processes of attention by regulating inputs 

 to the cortex. This problem will Ije discussed further 

 below. 



Slri(ijiaUid()tlwla7iiocnrtical Interrelationships 



An important role in cortical motor regulation has 

 been attributed (71, 72) to indirect afferents to the 

 precentral motor cortex from the globus pallidus 

 via the ventrolateral nuclei of the thalamus. De- 

 scending cortical influences to the pallidum may be 

 direct or may pass through the caudate nucleus. 

 These topics and the effects of interruption of certain 

 corticosubcorticocortical circuits in the production of 

 abnormal movement are discussed in Chapter XXXV 

 by Jung & Hassler. 



The pallidum is said to recei\c cerebellar afferents 

 directly \ia the brachium conjuncti\um (82) and 

 indirectly via the red nucleus (78), in addition to the 

 afferents from the putamen and caudate nucleus 

 (cf. 306, 350, 372). The caudate nucleus in turn may 

 be activated not only by cortical but also by thalamic 

 afferents. Afferent fibers to the caudate nucleus from 

 the so-called 'diffuse projection system' of the thalamus 

 (discussed by Jasper in Chapter LIII of this work) 

 have been described (102, 366), but their existence 

 has been disputed (344). Anatomical and physio- 

 logical data concerned with this problem have been 

 reviewed (410) with evidence for the existence of 

 thalamostriatal connections. 



Changes in the electrical activity of thalamic nuclei 

 and of the cerebral cortex have been observed during 

 stimulation of the caudate nucleus (195, 412, 434), 

 although some of these findings are still disputed 



(213). Since the existence of caudate-cortical connec- 

 tions is uncertain (309, 370, 412), it has been sug- 

 gested (412, 434) that the changes in cortical activity 

 from caudate stimulation take place via the pallidum 

 and thalamic and subthalamic nuclei through path- 

 ways including the ansa lenticularis (cf 306, 350, 

 372). These studies, however, do not shed any light 

 on the essential problem of the role of the striatum in 

 cortical motor mechanisms. Striatal effects are cer- 

 tainly capable of influencing 'motor' activities at 

 lower levels of the central nervous system as indicated 

 by the findings reviewed in Chapter XXXV by 

 Jung & Hassler in which the functions of the basal 

 ganglia, as gleaned from experiments of stimulation 

 and lesions of different nuclei, are discussed. 



Cerebellocerehral Interrelationships 



For a complete account of cerebral and cerebellar 

 interactions concerned with phasic and tonic inuscu- 

 lar activity, reference should be made to the chapters 

 by Brookhart, French, Jung & Hassler and Eldred 

 in this work.^ 



No specific role can as yet be assigned to the cere- 

 bellothalamic (82, 83, 104, 105) and rubrothalamic 

 (78, 447) streams of afferent volleys which relay in 

 the cerebellar nuclei and pass to the cortex via the 

 ventrolateral nucleus of the thalamus (cf. 457). Facili- 

 tatory (331, 332, 380) and inhibitory (332, 333) 

 influences on cortically-evoked muscular activities 

 have been disclosed by stimulation of neocerebellar 

 and paleocerebellar cortex (see Chapter LI by 

 Brookhart in this work), but it has not yet been estab- 

 lished whether these actions are mediated through the 

 pathways outlined above, or whether they occur exclu- 

 sively through spinal mechanisms (334). Some of the 

 evidence, however, would suggest that the cortex is the 

 place at which facilitation, at least, can occur (334). 

 An increase in the electrical activity of the motor 

 cortex has been described during stimulation of the 

 neocerebellum (456), but interpretation of these data 

 seems difficult. In fact, stimulation of the nucleus 

 \entralis lateralis produces varying effects on the 

 activity of different neurons in the motor cortex 

 (267, 268). Pyramidal cells which send their axons 

 into the pyrainidal tract may be excited. Howev-er, 

 their activity may be reduced by reason of lessened 

 excitation from cortical interneurons. The firing of 

 these interneurons is indeed abolished by stimulation 



^ \ comprehensi\'c study has been published by Dow & 

 Moruzzi (i2ia). 



