REGULATION OF FOOD AND WATER INTAKE 357 



their impaired motivation, react exaggeratedly to the removal of taste and 

 smell from the diet. They do not press the bar frequently enough to obtain 

 sufficient food. It is only after they have had a long period of experience 

 with the diet that they will work for it and demonstrate adequate regulation 

 when they are fed intragastrically. This can be very clearly shown by 

 providing the taste of food in addition to its injection into the stomach. If 

 a tiny amount of food is injected into their food cup while they receive their 

 full amount of intragastric injection, hyperphagic animals that are demon- 

 strating this motivational inertia when first beginning to work for food will 

 immediately display vigorous hyperphagia. They will work hard for food 

 only if they get a slight taste of the diet in addition to the intragastric 

 injection. They regulate precisely, work vigorously, overeat and gain 

 weight rapidly. If the taste is removed again, however, they immediately 

 relapse into a state of sluggish motivation. Therefore, the regulation that 

 they could display is concealed because they are not adequately motivated. 

 This shows clearly that taste acts as a powerful motivating stimulus to 

 enable animals with impaired motivation to regulate normally. 



THE ROLE OF TASTE IN THE FOOD INTAKE OF 

 LATERAL HYPOTHALAMIC ANIMALS 



Lateral hypothalamic lesions result in a syndrome of aphagia and 

 adipsia leading to death (Anand and Brobeck, 1951). However, if these 

 animals are kept alive by maintaining them with artificial tube feeding, 

 they will eventually recover (Teitelbaum and Stellar 1954), and their 

 recovery yields a great deal of information about the nature of the deficits 

 induced by the lesions. Teitelbaum and Epstein in a recent analysis (1962) 

 have shown that the lateral hypothalamic syndrome results from a com- 

 bination of deficits in both feeding and drinking from which animals 

 recover at diff'erent rates. There are four clear-cut stages in this recovery. 

 As shown in Fig. 8, first we see the stage of aphagia and adipsia : the 

 animal neither eats nor drinks anything and will die if not maintained 

 artificially. Then follows a stage of anorexia and adipsia in which the 

 animal can be induced to take highly palatable wet foods, such as wet 

 cookies, chocolate, or a liquid diet. It ingests appreciable quantities but 

 still does not eat enough to maintain its body weight. It still has to be 

 tube-fed. It is as though it is drawn to the palatable diet by appetite, not 

 driven to it by hunger. Taste provides sufficient motivation to induce the 

 animals to eat but the urge to eat has not sufficiently recovered to the point 

 where normal regulation can be demonstrated. However, the urge to eat 

 does return. This is seen clearly in Stage III. The animals regulate their 

 intake of the liquid diet and maintain their weight ; however, they are still 

 adipsic. In this stage, such animals can be trained to feed themselves 



