1702 



11 \M>li( ink hi- PHYSIOLOGY 



NEUROPHYSIOLOGY III 



,1 movement withoul jerkiness. This might Ik- accom- 

 plished by a controlling feedback proportional to the 

 velocity of the movement. In this view "cerebellar 

 tremor may be comparable to the oscillation of an 

 undamped scrvonicchanism in which the feedback is 

 remo\ ed." 



Ruch likens the cerebellum to the "comparator" of a 

 servomechanism which receives from the cerebral 

 cortex some representation of the command, and from 

 the muscle and other exteroceptors a representation 

 of the resulting movement. These, compared, may 

 result in a signal which when transmitted to the motor 

 cortex alters its commands to the muscles so as to 

 diminish the discrepancy. 



The higher integrative levels themselves, which 

 operate within a system of higher order, do not 

 escape the same basic mode of organization. Thus, 

 the whole nervous system will have to be viewed as a 

 functional hierarchy of systems, each of which in- 

 cludes subsystems and so on, a view already stressed 

 earlier by Weiss ( [30). At all levels of this hierarchy, 

 we shall find the same common principle of organi- 

 zation of sensorimotor functional units. 



A principle of circular regulation seems to govern 



the fundamental mode of relation which ties the 

 efferent to the afferent portions of the nervous system 

 cither inside the body or through the external me- 

 dium. Thanks to its self-regulating mechanism, each 

 working unit of this system assumes, in a given 

 range of flexibility, its own functional balance in 

 accordance with the requirements of the general 

 equilibrium which results in this internal unit con- 

 tributing to the effectiveness of the organism as a 

 whole. 



We are then led to the older concept of 'senso- 

 motility' of Exner, as well as to its more recent 

 expressions (43), to conceive the dynamic patterning 

 of nervous commands as a result of the continuous 

 stream of nerve impulses which is carried alony a 

 variety of circular paths that form closed loops at 

 various levels of an anatomically ordered structure 

 and which flows continuously from sensory receptors 

 to effector organs, as shown in figure 10. 



Space does not permit further discussion of the 

 several functional implications and the necessary 

 limitations of such a principle of organization in its 

 theoretical as well as practical aspects. Although we 

 may speculate concerning its broader significance 



fig. 10. Highly simplified 



diagram of the chief sensory, 

 associative and motor p.itlis 

 throughout the nervous system, 

 n hii ii illustj ates tin- circular 

 organization of tin- sensorimotor 

 N 1 in. .11s .it ,iiiv levels. Only the 



..iii|.iii infoi in. .1" its are 



repi est nted s , ,n r dh I sensoi j 

 connections to various higher 



iiims have been intention- 

 ally omitted 



