DRIVE AND MOTIVATION 



'O'D 



and stimulation studies show. The current hypothesis 

 is that neocortical and rhinencephalic structures exert 

 their influence directly through the hypothalamic 

 integrating mechanism; but we have very little direct 

 evidence on the anatomical and physiological path- 

 ways involved. 



Analysis of the sensory contribution to the arousal 

 and satiation of motivation shows that it is typically 

 a multisensory matter in which the influence from the 

 various sensory pathways is additive. As yet, however, 

 there is only a small amount of information showing 

 direct sensory contribution to the hypothalamic 

 mechanisms involved in motivation. 



The important role of the internal environment in 

 motivated behavior is thought to be mediated largely 

 through the hypothalamus. Particularly relevant are 

 the arousal of motivation by direct injection of sub- 

 stances into the hypothalamus and the failure of sys- 

 temically injected hormones to elicit motivation fol- 

 lowing hypothalamic lesions. 



The complexity of the neurophysiologies mecha- 

 nisms described here is greatly increased by two facts. 

 a) These various influences on the hypothalamic 

 mechanisms interact in the arousal and satiation of 

 motivated behavior in the sense that one kind of 

 influence may add its effects to another, b) The 

 possibilities for the arousal, expression and satiation 

 of motivation are greatly expanded by learning, 

 undoubtedly altering the underlying physiological 

 mechanism in some way as yet unknown. 



Electrical stimulation of the brain can serve to 

 reinforce learning and learned performance in much 

 the same way that food reinforces the hungry animal. 

 It is too early to speculate about the nature of the 

 mechanism involved here, but it is perhaps significant 

 that many of the reinforcing points within the brain 

 are known to be important parts of the physiological 

 mechanism involved in motivated behavior. 



Little has been said and little is known about the 

 mechanism for the execution of motivated behavior. 

 The hypothalamus has been thought of as a major 

 integrating mechanism in the expression of motiva- 

 tion, but not much is known about the spinal and 

 brain-stem reflex mechanisms invoked. Some good 

 evidence points to the role of the cortex in the spatial 

 and temporal organization of motivated behavior 

 (151 ), but space has not permitted discussion of this 

 very important question. 



A second neglected problem Ins to do with per- 

 ceptual changes in motivated behavior. We have dis- 

 cussed only the relatively nonspecific role of afferent 

 systems in the arousal of motivation, but the moti- 

 vated organism is highly specific and selective in its 

 perception of the environment, as many ethological 

 and psychological studies show. Unfortunately, we 

 have very little physiological evidence relevant to this 

 problem. 



\\ e have made onl) a start on the elucidation of the 

 physiological mechanisms underlying motivated be- 

 havior, but a basic core of knowledge and a general 

 orientation have been established. 



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