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IIWDBOOK OF PHYSIOLOGY 



XF.t KOPHYSIOI.OGY III 



CHEMICAL 8 PHYSICAL 



HORMONES 



9L000 TEMP 



OSMOTIC PRESS 



OHUGS 



REGULATION 



OF INTERNAL 



BALANCE 



FEEDBACK 



FROM 



1SUMMATORY 



BEHAVIOR 



fig. I. Schematic diagram of the physiological factors con- 

 tributing to the control of motivated behavior. Description in 

 text. [From Stellar (151).] 



is started b) hormonal triggering of the highest neural 

 mechanism which yields migrator) behavior. Then, 

 as new stimuli in the environment are encountered, 

 excitation in a succession of lower neural mechanisms 

 is built up and released by sign stimuli specific to 

 selection of territory, nest site and nesting materials, 

 fighting in territorial defense against intruders, mating 

 and care of the young. 



While the neurophysiologicaJ propositions of the 

 ethologists are quite speculative, their behavioral 

 analyses have been excellent and will provide a basis 

 for direct physiological investigations "1 the mecha- 

 nisms underlying motivation. Their work makes 

 possible the extension of Beach's phylogenetic com- 

 parisons to infrainammalian species and to kinds of 

 motivation other than sexual. Furthermore, they 

 oiler rich insights into the organization of motivated 

 behavior because of their insistence upon relatively 

 completi descriptions of patterns of motivated be- 

 havior as observed in naturalistic settings, in contrast 

 to the American psychologists' relatively artificial 

 laboratory testing oi isolated segments of behavior. 



One thing should lie apparent now about all of 

 thes< 1 entral neural theories; the) are based larger) on 

 inferences from behavior, for the) fail to take into 

 11 1 1 1 1 direct studies ol the central nervous system 



which might provide experimental evidence relevant 

 to the locus and properties of the postulated central 

 neural mechanism. Fortunately, there is now a large 

 and growing body of experimental data on the role of 

 certain central neural structures in the arousal and 

 integration of motivated behavior, and it is possible 

 to use this information in a specific and physiologically 

 concrete extension of the theories of Lashley and 

 Beach. This was done originally in i<) r >4 by the present 

 author (151) in an effort to arrive at a unified multi- 

 factor theory of motivation, general enough to apply 

 to many different kinds of motivation, across many 

 different species of animals. A brief summary of this 

 theoretical view will be given here in order to provide 

 an up-to-date physiological framework for the re- 

 view, later in this chapter, of the experimental evi- 

 dence we now have available on the physiological 

 basis of motivation. 



A schematic diagram of the physiological mecha- 

 nism believed to underlie motivation is shown in 

 figure 1. Look first at the diencephalic mechanism in 

 the middle of the diagram. As far as we can tell from 

 present experimental evidence, the major focus of the 

 neural system or the integrating mechanism respon- 

 sible for the arousal, execution and satiation of mo- 

 tivated behavior lies in the diencephalon, probabl) the 

 hypothalamus. Since ablation and stimulation of 

 restricted foci in this region of the brain result in either 

 increases or decreases in motivated behavior, it ap- 

 pears, furthermore, that it may contain two kinds of 

 functional areas which can be described operationally 

 as excitatory and inhibitory mechanisms. The basic 

 assumption here is that the arousal ol motivated be- 

 havior is determined directly by the output of the ex- 

 citatory mechanism, and the satiation of motivated 

 behavior b) the output of the inhibitor) mechanism. 

 Thus, there is believed to lie .1 reciprocal mechanism 

 which provides a basis for refined and graded control 

 ol motivated behavior. Whether the inhibitory mecha- 

 nism acts onl) on the excilalorv one as suggested in 

 some experimental work, and shown in the diagram, 

 or whether the two mechanisms exert their effects on 

 a common mechanism for the execution of motivated 

 behavior is still an open question. 



In any case, starting with this dual diencephalic 

 mechanism, the question then becomes: what controls 

 its .letivitv and therefore the arousal, execution and 

 satiation of motivated behavior? As I.ashlev and 



Beach suggest, the behavioral evidence implies that 

 three classes of factors ate operative. "' Sensory in- 

 fluences, operating through afferent pathways, physio- 



logicall) defined as specific and nonspecific, ma\ 



