CHAPTER L 



Central regulatory mechanisms — introduction' 



F . BREMER j University of Brussels, Brussels, Belgium 



THE PHYSIOLOGIST who IS faccd with the problem of 

 nervous integration hopes that eventually an illu- 

 minating synthesis will emerge from the experimental 

 findings which he accumulates. Aware of the sterility 

 of vitalistic evasions, he is a mechanist without illu- 

 sions. By an act of deterministic faith, he accepts the 

 theoretical possibility that all behavior may be ex- 

 plained in terms of the physicochemical activities of 

 the neuronal network, the structure of which, infinitely 

 complex though it be, appears to be decipherable. 



Indeed the functioning of the bulbospinal segments 

 of the vertebrate neuraxis is sufficiently regular to 

 permit its description in terms of the dynamic factors 

 brought to light by Sherrington and his school. The 

 bodily movements resulting from the processes oc- 

 curring in the integrating centers of the brain stem 

 and even of the projection areas of the cortex can be 

 interpreted as resulting from the activity of an input- 

 output system. The presence of motor projections in 

 many cortical areas, which until recently were con- 

 sidered to be exclusively sensory, provides anatomical 

 evidence for the fundamental homology between 

 cerebral mechanisms on the one hand and the reflex 

 mechanisms of the lower neuraxis on the other. This 

 homology is further illustrated by the ease with 

 which reactions of the so-called motor areas can be 

 evoked by aflTerent influences reaching them directly. 

 Similarly corticocortical synaptic transmission, at 

 least that involved in the callosal connections between 

 cortical areas, notably the auditory areas, of the two 

 hemispheres, shows a regularity of performance no 

 less striking than that of elementary spinal reflexes. 

 These experimental findings appear to justify the 

 description of the fundamental architecture of the 

 mammalian central nervous system as a progressive 



' The original was translated by Dr. Victor E. Hall. 



superimposition upon the segmental reflex arcs of 

 circuits of increasing complexity, all of which originate 

 in peripheral sensory mechanisms and end in motor or 

 secretory efTectors. The relatively unpredictable char- 

 acter of the processes occurring in the cerebral 

 neuronal network, according to this view, results only 

 from the participation of a colossal number of 

 synaptically connected cells. The infinity of possible 

 reaction patterns is made possible by the numerical 

 immensity of the neurons available. 



This confidence in the connectionist theory of 

 central functioning must be tempered by confession 

 of our ignorance of the nature of the supreme inte- 

 grating principle whereby partial activities are fu.sed 

 and coordinated .so as to produce the unity of the in- 

 dividual and the apparent spontaneity of his behavior. 

 Nevertheless, we can take the position as Louis 

 Lapicque did in giving the title The Nervous Machine 

 to an essay that, with the reservation that such a co- 

 ordinating principle may operate at the higher levels, 

 the nervous system may be considered as an assembly 

 of mechanisms. 



A machine is made up of operational parts con- 

 trolled bv components providing automatic regula- 

 tion. If we are to look on the nervous system as a 

 machine, this distinction raises the semantic difficulty 

 that the entire nervous system can be considered a 

 regulatory appartus. All its activities tend to restore 

 a dynamic equilibrium and to maintain its con- 

 stancy — through its incessant re-establishment. In 

 the regulatory processes information of extero-, in- 

 tero- or proprioceptive origin evokes appropriate 

 corrective responses by increasing some and decreas- 

 ing other centrifugal impulse streams. The regulatory 

 circuit may be considered to parallel the sensory and 

 eflfector innervations and thus to modify their activity. 



However, there apparently are also present in the 



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