THE PATTERNING OF SKILLED MOVEMENTS 



'697 



phalic source of volitional impulses must not lead us 

 to underestimate the certainly important role of the 

 neocortical structures in the process of elaboration and 

 initiation of voluntary movement. 



The fundamental problem, set by the nature of the 

 neurophysiological basis of the conscious decision 

 which finally liberates the patterned stream of nerve 

 impulses, remains untouched however. As Penfield 

 further emphasizes: "These questions impress them- 

 selves upon us for an answer. They bring clinical 

 physiologists face to face with psychologists and the 

 religious philosophers in what may be called a 

 common perplexity" (94). 



MECHANISMS OF PATTERNING AT THE NEURONAL LEVEL. 



The problem of the mechanisms implicated in the 

 patterning of central nervous activities clearly 

 remains unsolved. This field, hardly accessible to 

 direct experimental study, is open to theoretical 

 speculations inspired by various considerations (29, 

 61, 67, 92, 98, 130). With wisdom, Lashle) (68 

 thinks that "the law of parsimony requires that ever) 

 effort be made to explain all integration in terms of 

 the demonstrated modes of interaction of nerve cells 

 before some different and unknown process is pullu- 

 lated." 



Most of the hypotheses which are based upon the 

 functional dynamics of synaptic or ephaptic inter- 

 actions strive to designate the pan played in the 

 patterning of nervous aciiviiv by the structural 

 arrangement of the neurons into appropriate patterns 

 of interconnections. 



I 1 11 ■ study of nervous architectonics reveals a 

 great variety of organizations of the pol\ neuronic 

 structures. To the well-ordered grouping of the long 

 specific afferent and efferent paths in the nervous 

 organization may be contrasted the apparently 

 random distribution of the short neurons in the net- 

 work of the brain stem and of the associative sectors 

 of the cortex. The former is particularly suited to the 

 faithful transmission of the spatiotemporal feature of 

 an organized nervous message. But difficulty arises 

 as soon as we try to follow the destiny of these patterns 

 and their remodelling in the stochastic network 

 where, everybody agrees, the most complex inte- 

 grative operations are located 1 34). 



"There are some thousand million neurons in the 

 human cerebral cortex and each is a node in the 

 network whose strands are woven from the numerous 

 processes (dendrites and axons) that provide the 

 multiple synaptic contacts. Each node would be the 



converging point of scores of paths and each in turn 

 would project to scores of other nodes" (29). 



Many authors have speculated on the exceptional 

 functional properties that such an arrangement 

 could confer on the nervous structures which possess 

 it. Various theories have been proposed to explain the 

 functioning of these networks (21, 34, 68, 102). 



The anatomical complexity of the interneuronic 

 connections and the great capacity of these ensembles 

 to compensate after experimental destruction led to 

 the conception of a kind of functional undifferen- 

 tiation (equipotentialiiv). The mere numerical con- 

 sideration of the available cells in relation to the 

 different patterns of excitation possible leads us also 

 to exclude, at first glance, the hypothesis concerning 

 the existence of a specialized circuit for each con- 

 figuration of activity. In fact, each neuron of the 

 network can be engaged in various patterns of acti- 

 vation. The pluridimensional network thus offers an 

 infinity of possible configurations with a limited 

 number of elements ( 29). 



Eccles, lor his pari (29), postulated the existence 



in the interneuronic arrangements of the network of a 

 given structural specificity, inherited or acquired and 

 open in remodelling. It would sensitize given circuits 

 to given modes of activation defined in the afferent 

 sectors o| the system and would canali/c these actions 

 electivel) through the activating structures <>i efferent 

 s\sicnis. The shunting of these circuits of activity 

 could also be submitted to the modulating actions oi 

 a peculiar type. In this connection, Eccles tries to 

 confront on a neurophysiological plane the problem 

 of the modulating influences of the "will.' "There can 

 In- no doubt that a great pari of the skilled activity 

 evolving from the cerebral cortex is stereotyped and 

 automatic. But it is contended that it is possible 

 voluntarily to assume control of such action" (29). 



I uive an account of such control, Eccles is led to 

 pustulate the existence of a "field of influence 1 capable 

 of modifying the intrinsic spatiotemporal activitv ol 

 the neuronal network. The quantitative aspect of tin- 

 spread of activiu in neuronal networks and the 

 physical implications of such a mechanism are taken 

 into consideration and lead Eccles to suppose a 

 so-called "detector function' proper to these neuronal 

 networks which he makes the basis of the essential 

 operations of the "matter-mind traffic' (29). 



In this field we can, with Eccles, conceive the 

 pattern of volitional impulses emerging from the 

 integrative network as being determined by three 

 factors: a) the afferent input and its spatiotemporal 

 characteristics; b) the microstructure of the neural 



