i68 4 



II \\l)l!i ink ( il 1'IIVMUI.OGY 



NF.LROI'HYSIOLOGY III 



fig. 3. Electromyographic analysis of the synergy between 

 the proper flexor of the index and tin- extensor carpi radialis. 

 Left: Upper line, activity of the extensor carpi radialis which 

 slums the tonic functioning of a motor unit as detei ted by the 

 coaxial needle. Third lint, activity of the flexor muscle. Second 

 line, the mecanographic record showing a very slight move- 

 ment of flexion of the index with the corresponding activity of 

 the flexor muscle (grouped discharges of few motor units). The 

 (.hi esponding synergistic activity of the extensor carpi is shown 

 in the phasic increase of the frequency of discharges of the 

 active unit Right: Same conditions, but the two muscles are 

 initially silent. The index linger is progressively extended as 

 shown by the meclianographic record. Note the simultaneous 

 start of the activity in the two muscles and the recruiting of new 

 units as the movement progresses. [From Tournay & Fessard, 

 unpublished obsei \ ations 



in .1 hundred different ways. A given movement can 

 never be reproduced identically. We can never find 

 two patterns of activity repeated twice in succession 

 which are strictly superposable. At the level of the 

 muscle itseli the SpatiotemporaJ pattern of recruit- 

 ment of the motor units implicated in a voluntary 

 movement is never absolutely identical. 



The innate mechanisms invoked in fundamental 

 synergic action no longer appear to have the impera- 

 tive and rigid form that Duchenne de Boulogne as- 

 signed to them. The studies of Livingston el al. (78) 

 on the synergic action of the radial muscles involved 

 in the flexion of the fingers of the hand reveal the 

 extreme plasticity of the play of these 'instinctive 

 associations.' The radial muscles behave in different 

 ways, adapting themselves to the changing cir- 

 cumstances of execution of die movement. The) ma) 



even lie COmpletel) relaxed when their action would 



be mechanically superfluous. Winslow (134) had 



"I-. noticed this •economical aspect' which 



characterized die intervention of die muscles which 



pan) a movement. "In certain cases, the 



moderators do not acl .11 all, their action being sup- 

 plied by the foreign resistance or onl) b) die weight 

 11I die pari lo which the) are al lathed." 



The problem ol patterning of skilled movements 

 confronts us here in all iis bewildering complexity, 

 particularl) when we undertake 10 siudv die reac- 

 tions of an entire organism where each partial 



mechanism is dependent upon the functioning of the 

 whole. This complexity helps us to anticipate that, 

 among the neurophysiolosiical mechanisms brought 

 into play in such operations, there will be included 

 components of a high level, psychological as well as 

 reflex, some acquired b) learning as well as others 

 which are congenital. 



The problem of the neurophysiological basis of 

 the patterning of skilled movements must be defined 

 here in terms of "coordination." Following Weiss 

 I 1 ;oi we mean by coordination "the selective activa- 

 tion of definite groups of units in such combination 

 that their united action will result in an organized 

 peripheral effect that makes sense. . . ." 



We can already begin to see, in the light of this 

 first analysis, that the problem of nervous coordina- 

 tion can no longer be stated in the simple form, 

 classically accepted, of an innervation exerting 

 antagonist effects on the extensor and flexor muscle 

 groups. We must seek for a mechanism which can 

 select a privileged combination of muscles from 

 among a considerable variety of possible combina- 

 tions. 



In this connection, two fundamental questions 



Add I 

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L,.E.i I 



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■ 1 ■»iw n n>Mm»i»i»w»» i | » 1 1 f« « »«« w i 



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1 11. 1 Pattern of acti\ ities ol (he muse Irs of the thumb in .1 

 writing movement l.lrctroinyographic activity is detected I >x 

 mm ins ol live coaxial needles from the following muscles: Add. 

 I, adductor policis, ( / Ext. I. extensor hrevis policis; Lg. Ext. 

 I, extensor longUS policis, / / .'. l /. flexor longUS policis, and 



Ct. Ah,l /, abductor brevis policis. I In subject, in .1 normal 

 writing posture, is asked to follow the contour of a letter l> 

 drawn on a metallic plate, with a metallic stvlus. The current 

 going from the stvlus to the plate is switched oil when it passes 



across regular!) arranged isolating horizontal bands. Thus, 

 iIm ..1 the record relates the different phases of the 

 •..in' nt wilh the activity of the muscles. I From Tuurnav & 



Paillard, unpublished observations.) 



