DRIVE AND MOTIVATION I 52 I 



35 20 ?5 i0 15 



LOG MOLAR CONCENTRATION NoCL 



-'0 ■ i5 .10 .15 



LOG PERCENT CONCENTRATION OF SUGAR 

 IN TEST SOLUTION 



I I II I III 1 1 I II MM 1 1 I llllll 



I 





 0001 



J 1 I I I Mil I I II I llll I 1 1 



MOLAR CONCENTRATION OF SACCHARINE 



WATER TESTS LOG MOLAR CONCENTRATION OF ALCOHOL 



fig. 4. Preference-aversion curves lor different foods offered in solution, showing fluid intake 

 as a function of the concentration ■ >! the solution. The sodium chloride, the glucose and fructose, 

 and the saccharin functions are based upon 1 hr. of drinking in the single stimulus method, the 

 alcohol function is based on 24 hr. drinking of alcohol ami watei in the two-bottle method. [The 

 sodium chloride data are from Stellar el al. (153); the sugar data, from MeCleary (95) ; the saccharin 

 and alcohol data, from Stellar, unpublished observations 



cellulose, at much lower percentages of adulteration 

 than normal rats. This result suggested the importance 

 of changes in the operated animal's reactivity to the 

 sensory stimuli provided by the diet, possibly even 

 in the original overeating of regular laboratory food. 

 This hypothesis was, in part, confirmed by the finding 

 that hyperphagic rats ingest more of the powdered 

 diet when 50 per cent glucose is mixed with it, and 

 less when a low concentration of quinine is added or 

 when the food previously given in the form of pellets 

 is presented in powdered form — neither of which 

 changes influence the intake of normal rats. Thus, 



whether a lesion of the ventromedial hypothalamus 

 leads to overeating or undereating, relative to normal, 

 is a function of the nature of the sensors stimuli pro- 

 \ ided by the diet. 



Two additional results are of note here, a) Rejec- 

 tion of cellulose-adulterated food was also observed in 

 rats with similar lesions that did not become hyper- 

 phagic, suggesting the possibility that the refusal to 

 eat certain foods might be dependent upon structures 

 outside of the inhibitory feeding mechanism in the 

 ventromedial hypothalamus, b) Hyperphagic rats 

 that are not allowed to become obese do not respond 



