1 694 



II Wllld il iK i IF PIIYMOI IICY 



NEUROPHYSIOLOGY III 



find a predominance of the right hand associated 

 with a dominance of the left hemisphere. It is known 

 that no clear differences in the organization of the 



cerebral cortex have been found between the two 

 hemispheres. The coexistence of speech disorders with 

 lesions of the left hemisphere should draw attention 

 to this problem. The study of the apraxias reveals, 

 on the whole, the dominating control exerted by one 

 of these hemispheres, the so-called •major hemi- 

 sphere," upon the other. The lesions of the 'minor 

 hemisphere' cause disorders of unilateral character 

 which are more easily compensated than the bilateral 

 ones following a lesion of the major hemisphere. 



The origin of this dominance is still controversial. 

 The suggestion that inequality of vascularization 

 might cause an asymmetry in the development of the 

 two hemispheres was once advanced by anatomists. 

 It can no longer be sustained today. As observed 

 by Tournay (117), the maturation of the left side may 

 be more advanced than the right side in the future 

 right-handed child. The role of learning seems, 

 however, to be predominant, as shown by the remark- 

 able compensation observed to follow hemispher- 

 ectomv in young subjects (62, 126). 



Neurophysiologies Data 



Confronted with the complexity and the difficulty 

 of the problems brought up by the clinicians, the 

 neurophysiologist appeared rather helpless, until 

 recendy. However, the ever increasing improvements 

 in his experimental techniques have now given him 

 new inc. ins of progress. Indeed it is to the recent 

 development ol electrophysiological methods oi 

 exploration of cortical activities in man and to the 

 technical ability ol brain surgeons that we owe the 

 opening of a new chapter in the physiology of volun- 

 tary action Thus, the greal neurosurgeon Penfield 

 does not hesitate to claim: "There is enough evidence 



lilable from the study of the human brain for 

 consideradon of the problem of voluntary movement 

 on .1 physiological basis," and he invites the neu- 

 rologist to examine objectively the new evideno 

 ■•without the bias from current clinical teaching 



It is now beyond doubt thai the idiokinetic patterns 

 ..I activity which .inhn. ne the cortical motor key- 

 board do not depend upon the origination of nerve 

 impulses in the rm in.il motor area itself. The 'motor 



power of i I ■- activities' conies from somewhere else 



Therefore the motor cortex appears as a funnel oi 

 convergence for the stream ol patterned impulses 

 which produce voluntary movements. 1 he disorders 



of the praxic function allow us to glimpse the com- 

 plexitv of the mechanisms implicated in this canali- 

 zation of the stream of sensory afferent influences to 

 the core of the integrative structure where the plan- 

 ning of the act takes place. A series of questions thus 

 present themselves to the neurophysiologist. What 

 are the nervous structures implicated in the successive 

 stages of this transformation? By what paths are the 

 transmission and the transformation of the sensory 

 patterns carried through the associated structures to 

 the integrative structure where the messages which 

 will animate the cortical instrument of motor com- 

 mands are elaborated? What are the nervous mecha- 

 nisms which make possible this selective patterning of 

 excitation within the neuronal sets of the cortex.' 



CORTICAL PARTICIPATION IN THE ELABORATION OF 



voluntary movement. It has become classic to 

 localize the most complex integrative elaborations in 

 the core of the neocortical nervous structures. The 

 long controversy which, until the modern period, 

 divided the believers in a functional globalism from 

 the partisans of the specific activity of anatomically 

 localized structures is likewise traditional. To admit 

 that the brain functions as an indissociable whole 

 must not prevent us from trying to determine the 

 nature and to analyze the mechanisms of its functional 

 cohesion. Thus, the pathological anatomy of praxic 

 disorders cannot but bring us several important 

 orienting facts concerning the particular role of 

 certain associative areas of the cerebral cortex in the 

 elaboration of the components which cooperate in the 

 patterning of voluntary commands, more particularly 

 the parietal areas with the neighboring gnosic regions, 

 the frontal areas and especially the regions anterior 

 to the principal motor area. 



Now, where in these structures can we place the 

 higher level to which Jackson attributed the supreme 

 power of unifying sv nthesis? .\i iirsi si._;lu, do ,iv ailable 

 argumenl permits us to .issitm 10 it .1 precise locali- 

 zation in the ion- ol the neocortical structures, To 

 propose that this integrative operation results from 

 the complex interplay between the diverse functional 

 areas ol the cortex thus offers an acceptable hypoth- 

 esis. Histological and neuronography methods have 



revealed the richness of the Connections which lie tin- 

 various sectors ol .1 cortical hemisphere together anil 

 the importance of the liaisons which associate them 



liv callosal paths with the homologous regions of the 

 opposite hemisphere. Our present knowledge oi the 



Inn mvelo- and cv toarehitecionie Organization ol the 

 cortical structures is still too imprecise to permit us 



