CENTRAL CONTROL OF RECEPTORS AND SENSORY TRANSMISSION SYSTEMS 



759 



its action than previously believed. XN'hat may be 

 taken for sensory pathways, because they convey 

 sensory-evoked signals in a centripetal direction, turn 

 out to be more variable and more widespread in their 

 transmission of impulses in the waking state. The in- 

 creased variability seems to be due to active inter- 

 ference by a centrifugal mechanism. The widespread 

 distribution of sensory-evoked impulses allows a more 

 elaborate intermingling of sensory with other signals 

 throughout various parts of the brain. Experimental 

 evidence favors a lessening of our ccjnceptual isolation 

 of sensory from motor and other central mechanisms. 

 The nervous system appears to be made up less of 

 independent linear pathways than of mutually inter- 

 dependent loop circuits which stitch together the 

 \arious parts of the brain into a functional whole. 



Along ascending as well as descending projections, 

 the brain-stem reticular formation and the cerebral 

 and cerebellar systems linked closely with it seem to 

 modulate impulse traffic in a continuous action that 

 modifies the composition of perceptive as well as pro- 

 jective neural patterns. The losses and distortions of 

 signals brought about by this mechanism favor the 

 conclusion that some teleological mechanism is at 

 work; this appears to be designed to diminish the in- 

 volvement of higher centers with signals that have 

 little immediate significance for the animal. Thus, 

 sensory signals appear to be subject not only to error, 

 in the sense projected by Descartes, but also to some 

 purposive central control. A further examination of 

 these mechanisms will help us to understand many 

 problems of absorbing interest in neurology, psychia- 

 try, psychology and philosophy. 



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