114 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



Motor and Sensory Functions Persisting 

 After Hemispimectomy 



Dandy (no) was the first to perform hemisphcrec- 

 tomy. This intervention in adults with hemiplegia of 

 long standing, or in cases of infantile hemiplegia (241 ), 

 produces no further increase in motor deficit. Cases 

 published in the literature have been summarized 

 (180) and a recent monograph in this subject is avail- 

 able (244). Briefly, when the hemispherectomy is 

 carried out with the intent of leaving most of the basal 

 ganglia, thalamus and hippocampus intact, the re- 

 covery of walking is rapid and some global movements 

 of the opposite half of the body are present {183). The 

 improvement in motor performance reported in some 

 of the cases has been attributed to the reduction of 

 spasticity which frequently follows hemispherectomy. 

 The Babinski sign may be present or absent. The 

 sensory status varies from subject to subject but, while 

 the gnostic sensibilities are abolished, some gross, 

 superficial and deep sensations, which usually have a 

 painful component, are still present. 



In the case of more nearly total hemispherectomy, 

 as the ones performed originally by Dandy (no) 

 which included the ablation of the head of the caudate 

 nucleus and probably indirect alteration of vascular 

 origin in thalamic and subthalamic centers, walking 

 movements were never possible. Impairment of motor 

 functions following hemidecortication were discus.sed 

 by Walker & Fulton (459) in relation to the phyletic 

 aspect of the problem. Other clinical and experimen- 

 tal findings will be found in the monograph cited. 



MAJOR AFFERENTS TO CORTICAL AREAS CONCERNED 

 IN SENSORIMOTOR INTEGRATION 



Tlmlamic Afferents 



The studies of Minkowski (320, 321-324) appear to 

 have been the first experimental attempt at a syste- 

 matic analysis of the connections of cortical precentral 

 and postcentral areas which are involved in sensori- 

 motor activities. Numerous studies have been pub- 

 lished both before and since that time dealing with 

 thalamic afferents to the sensorimotor cortex in the 

 rat (94, 461), rabbit (173, 376, 411) and primates, 

 including man (14, 90, 93, 103-105, 364, 393, 453- 

 455). It is now well-estab'ished that the precentral 

 areas 4 and 6 receive fibers from the ventrolateral 

 nuclear groups of the thalamus (cf. 90, 378, 418, 457) 

 which increase in size at higher levels in the phyletic 

 scale concurrentlv with the increased size of cerebellar 



hemispheres in higher mammals (393). The number 

 of fibers reaching area 6 from the thalamus increases 

 rapidly in higher primates (cf. 458). Clertain topo- 

 graphic patterns of distribution in areas 4 and 6 have 

 been described for these fibers in relation to the posi- 

 tion of their cell bodies in the thalamic nuclei (cf. 90, 

 455. 458)- Thalamocortical connections to parietal 

 areas 5 and 7 originate from the nucleus lateralis 

 posterior of the thalamus (90, 96, 353J. 



In the rat, an overlap exists between the excitable 

 cortex and the cortical area receiving projection 

 fibers from thalamic nuclei relaying sensory informa- 

 tion (186, 252). The problem of the existence of 

 sensory projections to the precentral cortex ot pri- 

 mates must also be considered (104, 105, 136; cf. 458); 

 it is di-scussed in Chapter XVII by Rose & Mount- 

 castle in this work. There is no general agreement that 

 cutaneous sensibilities are confined to the postcentral 

 gyrus, as has been suggested (290, 478), since potentials 

 have been recorded in the precentral cortex from 

 stimulation of either muscular or cutaneous nerves 

 after postcental ablation (287, 387). Stimulation of 

 dorsal roots was alread\- known to produce responses 

 in the motor cortex (476), but they had ijeen tenta- 

 tively interpreted as carrying proprioceptive intorma- 

 tion (474). In man, sensations persist on stimulation 

 of the precentral gyrus after postcentral resection (357, 

 358) and frequently involve a 'desire to move.' 



The mapping in the cortex of responses from deep 

 somatic stimulation has given conflicting results. Some 

 authors consider that kinesthetic sensibility is exclu- 

 sively represented in the postcentral gyrus and is 

 based on proprioceptive afferents from joint and 

 fascial receptors rather than from muscular aflferents 

 (337, 338). According to other authors, deep sensi- 

 bility may be largely represented in precentral motor 

 cortex (5, 8). Overlapping representations of widely 

 separated peripheral points were found, with the 

 same basic arrangement of major body parts, similar 

 to that seen in the tactile representation (5). The 

 proprioceptive nature of impulses capable of evoking 

 responses in the somatosensory cortex of the cat (54, 

 313) has also been demonstrated (21). Responses 

 evoked in the motor cortex ijy stimulation of muscle 

 nerves are not abolished In- remo\al of the cerebellum 



(387)- 



A progressi\-e corticalization ot the function ol 



weight discrimination has been observed (383, 385, 



386). The elaboration of this type of perception, 



which would seem to require the participation of 



proprioceptive sensiliilities, involves the cortex of the 



parietal lobe. Damage to any portion of the parietal 



