758 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



FIG. 15. Effect of nitrous oxide on long latency bilateral reticular formation responses to tooth 

 pulp stimulation. Although the lemniscal response to tooth pulp stimulation is not perceptibly 

 aflfected by nitrous oxide-oxygen inhalation, responses elicited within both ipsilateral and contra- 

 lateral reticular formation practically disappear after 5 min. of such inhalation. Recovery is nearly 

 complete 15 min. later. [From Haugen & Melzack (34).] 



tures implicated in both positive and negative rein- 

 forcement undoubtedly participate in the central inte- 

 gration of both sensory and motor mechanisms. These 

 structures are anatomically linked with the extra- 

 lemniscal, diffusely projecting and extrapyramidal 

 systems as well as the phylogenetically older parts of 

 the cortex and brain stem. 



There has long been a quest to know how nerve 

 signals might be 'read' and how they might be gi\en 

 'value.' We are now certainly closer to knowing where 

 such events take place even though the how is still 

 unanswered. Clearly the cortex is not the first step in 

 sensory integration. During wakefulness sensory inte- 

 gration is taking place continuously and dynamically, 

 beginning with the farthest afferent outposts. This 

 involves an erosion of information that originally 

 started into the nervous system and an intrusion of 

 influences which are based upon the animal's previous 

 experience as well as its momentary disposal of atten- 

 tion. This implies that there is a reduction and distor- 

 tion of sensor\-cvoked signals from the acttial nature 

 of the stimulating world. Perhaps 'value' is likewise 

 inserted into the complex at these early stages of 

 sensory integration. Certainly significance to the 

 organism appears to be a guiding principle with 

 respect to the operation of sensory control mecha- 

 nisms, hence a survival of incoming impulses in the 



unanesthetized brain would appear to he jnima Jacie 

 evidence of their significance. 



In order to bridge the gap between neurophysi- 

 ology and psychology, it is necessary somehow to 

 determine the neuronal mechanisms underlving be- 

 havior. A principal difliculty appears with the at- 

 tempt to interpret the fimction of the whole out of its 

 parts. Whereas the beha\ ior of separate parts could 

 be made out from an analysis of the interaction of one 

 part with another, these parts will not add together 

 in any simple fashion to account for the beha\ior of 

 the whole. There ha\e been recent attempts to char- 

 acterize the differences between linear cause-and- 

 effect relationships and the more inxolved dynamics 

 of a large number of mutually interdependent systems 

 in simultaneous action (55). The authors use the term 

 'trans-action' to signify the latter kinds of operations 

 and to contrast them with more limited 'interaction' 

 systems. .Attempts ha\e been made to interpret some 

 of the transactional mechanisms invoked in \isceral 

 sensation and emotional expression (54). 



SUMM.XRY 



Recent experimental evidence, drawn largely from 

 the studv of animals without central anesthesia, indi- 

 cates that the nersous .system is much more plastic in 



