REGULATION OF FEEDING AND DRINKING 



Others offers an opportunity for studying the functions 

 of the brain stem in a manner not revealed by analysis 

 of any one regulation alone. 



Another type of interrelationship deserves mention. 

 Food intake is not an independent variable in energy 

 e.xchange, since it is the source of all the energy 

 aniinals have available for heat production, work and 

 storage either as growth or fatness. The common 

 knowledge that body weight of adult subjects tends 

 to remain constant is evidence that there is regulation 

 of the four variables as well as of each one, alone. 

 In other discussions of this subject the hypothalamus 

 has been proposed to be the part of the nervous system 

 responsible for the 'automatic" features of the regula- 

 tion of energy exchange, and heat production has 

 been suggested as the common denominator between 

 food, work, storage and temperature regulation (i8, 

 80). These conclusions are based upon reports that 

 lesions in .selected regions of the hvpothalamus may 

 alter food intake (6, 20), body temperature (73), body 

 weight or spontaneous activity (43, 57), and al.so 

 upon ev'idence from normal animals revealing changes 

 in other variables when one of them is arljitrarily 

 changed by the investigator. The idea that the hypo- 

 thalamus integrates these regulations, although hypo- 

 thetical, seems to be generally accepted. It is being 

 studied further in the laboratory by examining the 

 effectiveness of temperature regulation in animals 

 with disorders of feeding, and by searching for other 

 possible correlations between deficits of regulation of 

 activity, food intake and heat exchange. 



LEVELS OF NERVOUS CONTROL 



Our present understanding of how the ner\ous 

 system achieves the regulation of feeding and drink- 

 ing may be summarized in a few paragraphs. In 

 higher animals the brain stem, including the nuclei 

 and primary connections of the cranial nerves, is the 

 level most directly concerned. The basic patterns are 

 probably reflex in nature, requiring integrated motor 

 activity of trigeminal, facial, glossopharyngeal, vagal 

 and hypoglossal nerses, while the sensory com- 

 ponents of these as well as many other nerves are 

 playing their part. For almost any animal, including 

 one which has just eaten, food is a stimulus for these 

 reflex responses; when there occurs an adequate 

 sensory stimulation, animals move toward food, in- 

 vestigate, eat and swallow it. Reflexes of attention, 

 approach, examination, incorporation and rejection 

 appear to be important. Little is known of these 



mechanisms, however, and it is not clear just how 

 much of feeding behavior can be designated as reflex 

 and how much may be either conditioned responses, 

 learned behavior or .some other type of more highly 

 organized activity. It seems desirable to attempt to 

 learn more about these reflexes because neuro- 

 physiology has so often gone forv\'ard by way of studv 

 of reflex mechanisms. 



Pertinent data have been obtained from studies of 

 the behavior of animals with lesions at selected levels 

 of the neuraxis, and of unanesthetized animals during 

 stimulation or perfusion of discrete areas within the 

 brain. Experiments by Miller & Sherrington (62) 

 and liy Bazett & Penfield (15), using decerebrate 

 cats, showed that simple feeding responses are pos- 

 sible after remo\'al of much of the mesencephalon 

 and all of the more rostral portions of the brain. Their 

 decerebrate animals were capable of reflex chewing 

 and swallowing and of reflex rejection of certain 

 materials. Bazett & Penfield noted purring after 

 their cats were fed which suggests that a certain de- 

 gree of 'satiety' can occur even at the reflex or seg- 

 mental level. (Sherrington's reference to 'spinal 

 hunger' is found below.) 



The function of the hypothalamus, the next higher 

 level, is assumed to be quantitative, as already stated, 

 as if this part of the brain adjusts energy intake to 

 expenditure. The medial hypothalamus is believed 

 to take part in reactions of satiety, while the lateral 

 portions are responsible for appetite. After destruc- 

 tion of the lateral regions, animals fail to eat (6, 33); 

 in some cases the failure persists until death, in others 

 it is transitory or may be relieved following a period 

 of artificial feeding (8, 67, 86). Medial lesions, by 

 contrast, lead to overeating and obesity in all species 

 studied including man (20, 22).' When the lateral 

 mechanism is stimulated in unanesthetized animals, 

 feeding occurs (7, 23, 30, 53). Stimulation of the 

 medial region, as well as of certain other portions of 

 the brain, induces what appears to be satiety. This 

 was discovered by Olds (70) and others have con- 

 firmed his observations. In theory, the interaction 

 of these two hypothalamic regions might account for 

 most of the quantitative aspects of regulation of food 

 intake, since the cerebral cortex and other locations 

 in higher levels might affect the appetite via the hypo- 

 thalamic mechanisms. This, howe\er, is not known 

 and is not necessary, since the cortex might act upon 



' A convenient means of destroying these regions in mice 

 is by the intraperitoneal injection of gold thioglucose (56, 58). 

 The resulting obesity is like that of animals with lesions pro- 

 duced in the hypothalamus by electrolysis (32, 54). 



