I -,Jcl 



ii \M)in ii ik i ii riiNMi ii ni;". 



M i Rl (PHYSK 'I i ICY in 



the fact tli. u sex hormones .uc ineffective following 

 discrete lesions in the ventral hypothalamus jusl 

 anterior to the pituitary stalk (35). 



In one striking case, it has been shown that am- 

 phetamine, an appetite depressant, selectively acti- 

 vates the ventromedial hypothalamus in the anesthe- 

 tized eat (32). While this finding suggests that the 

 vile of action of amphetamine may he the hypothala- 

 mus, it seems clear that this cannot lie die sole site of 

 action since amphetamine can still depress the appe- 

 tite of the rat after bilateral ablation of the ventro- 

 medial hypothalamus (155). 



finally, we have the excellent example of speci- 

 ficity of hormonal action on the nervous system in the 

 work of Bonvallet et al. (24). They showed that epi- 

 nephrine had its effects on restricted loci in the 

 mesencephalon in its activation of the waking EEG 

 pattern, and in the facilitation and inhibition of spinal 

 reflexes. 



Results such as these make it most interesting to 

 ask about the mechanisms and sites of action of other 

 internal environmental changes that are known to be 

 important in motivation. Mow does insulin affect the 

 nervous system to produce its enhancement of hunger; 

 how does the salt deficiency of the adrenalectomized 

 rat lead to salt hunger, thiamin deficiency to thiamin 

 hunger; etc.? Ii seems unlikely that there are separate 

 'receptors' in the hypothalamus for each of these 

 chemical and physical changes in the internal environ- 

 ment. It is possible that there are a limited number 

 of overlapping mechanisms sensitive to internal 

 changes and that such specificity as does occur in the 

 selective arousal of motivated behavior might be (he 

 joint outcome of a particular combination of internal 

 and sensory variables. 



Interaction »/ Feu im 1 



It is quite obvious from the foregoing that it is as 

 important to understand the joint action of the various 

 fai tors contributing to the mul til actor control of moti- 

 vation as it is to know their individual influences. A 

 number ol siudies approach this (|uestion of the inter- 

 action of factors. I he problem is well illustrated in I he 

 case ol specific hungers lor solutions of sodium chlo- 

 ride, glucose and saccharin I Jo, <r,, I y;, [66). In all 



three ol these i ases, the ingestion of the solution in- 

 i reases a- a i don oi die concentration up to a cer- 

 tain point and then decreases Illy. p. This lawful 



pattern of ingestion is determined by a number of 



i." i perating together, in Some of the drinking, 



particularly ai the lower concentrations, is produced 



by dehydration since water deprivation or hypertonic 

 saline injection will increase the ingestion of the weak 

 concentrations (95, 153)- b) The increasing intake as 

 a function of concentration over the lower ranges 

 seems 10 be a result of increasing intensity of taste 

 stimulation, for in the case of sodium chloride, it quite 

 clearly parallels the increasing discharge of the chorda 

 tympani in response to increasing concentrations of 

 sodium chloride solutions (115). And in the case of 

 saccharin, the only thing known to vary with concen- 

 tration is taste. 1 ' The decreasing ingestion in the 

 higher ranges of concentration seems to be produced 

 by two factors. One is a second sensory factor, a nega- 

 tive taste factor (bitter) in saccharin and possibly 

 pain in sodium chloride ingestion. A second factor is 

 a consequence of the ingestion of hypertonic solutions, 

 namely dehydration. The separation of the negative 

 taste factor and the dehydration factor is seen in the 

 ingestion of salt solution by rats with esophageal 

 fistulas (153). These animals take decreasing amounts 

 of higher and higher concentrations of sodium chlo- 

 ride, suggesting a negative sensory factor, but the 

 drop-off with increasing concentration is nowhere 

 near as rapid as it is in the normal animal. Secondly, 

 the animal with a fistula does not reduce its intake oi 

 hypertonic saline following water deprivation but 

 rather increases it, emphasizing the role of postinges- 

 tion dehydration. (/) Finally, in the ease of salt 

 hunger at least, the internal environment is important, 

 for as it is increasingly depleted of salt following 

 adrenalectomy, the ingestion of salt solutions of all 

 concentrations increases (10, 55). 



Other instances of the joint operation of several 

 variables in the control of motivated behavior have 

 not been as completely worked out but are of interest 

 because i hey provide more information on the central 

 neural mechanism. Beach's report I i 2 > of the restora- 

 tion, bv sex hormone injection, of sexual motivation 

 losi through cortical lesions is one good example. 



Another is the reporl ol Brooks (36) that neither de- 

 cortication nor olfactory bulb ablation in die male 

 rabbit eliminates sexual behavior, but a combination 

 of the two does. A third is (he report of Schreiner & 



Kiing (136) that castration destroys the hypersexu- 

 ality induced in male Cats bv amv gdalectomv . 



Perhaps one of the better siudies showing the joint 



contribution of two or more factors to the control of 

 motivated behavior is the work of Teitelbaum (156) 

 who investigated the changes in the sensory control ol 

 eating produced by ventromedial hypothalamic 



lesions, lie found that hvperphagic rats reject pow- 

 dered laboratory food, adulterated with nonnutritive 



