C: H A P T E R X L V 1 1 



Regulation of feeding and drinking' 



JOHN R. BROBECK 



Department of Physiology, University of Pennsylvania School of Medicine, 

 Philadephia, Pennsylvania 



CHAPTER CONTENTS 



Sensation and Discrimination 



Behavior, Comparative Ethology and Psychology 



Significance of Nervous System 



Interrelationships and Integrations 



Levels of Nervous Control 



Central Perception 



Supplementary Mechanisms 



Thirst 



Locomotor Activity 



Summary 



A DISCUSSION of feeding and drinkins;, of appetite, 

 satiety, hunger and thirst, requires a knowledge of 

 many other functions of the ner\ous system, and it 

 may be well to note in the beginning that if certain 

 other phenomena were better understood, a more 

 adecjuate account of regulation of food and water in- 

 take would be possible. 



SENSATION AND DISCRIMINATION 



One of the important missing keys is a satisfactory 

 theory of sensation in general. Sensations associated 

 with hunger and thirst are so vix-id and so universally 

 known that they must be included in any explana- 

 tion of feeding and drinking, and yet they cannot be 

 explained nor can they be described very much better 

 than Sherrington did in his essays on general sensa- 

 tion in 1900 (77). Although Cannon & Washburn 



' Preparation of this review has been aided by a grant 

 from the National Science Foundation. Portions of the review 

 are taken from an earlier review by the same author (19). 



(25), and Carlson and his associates (26) identified 

 gastric contractions as the source of hunger pangs 

 experienced in the epigastrium, while Cannon (24), 

 Gregerson (40) and others have emphasized relative 

 dryness of the oral and pharyngeal membranes as a 

 stimulus for thirst sensation, the mechanisms by which 

 these and other sensations are perceived remain un- 

 known (in spite of careful investigations of sensory 

 pathways of spinal cord and brain, as reviewed else- 

 where in this Handbook). There is no hypothesis which 

 explains in a quantitative way how the organism 

 regulates either eating or drinking on the basis of 

 sensory experience. 



Sherrington's review contains another idea which 

 is supported by more recent experiments, namely, 

 there may be a type of perception taking place within 

 the nervous system as a stimulus to eating or drinking. 

 Sherrington wrote as follows: " 'Hunger' feeling (and 

 'thirst' feeling) are held, therefore, to originate in 

 impressions elaborated by the bulbar centres re- 

 ceiving the roots of those [ninth and tenth] nerves. 

 These centres are perhaps specially sensitive to those 

 qualities of the circulating blood which depend on 

 intake of food, much as the bulbar centre receiving 

 the lung branches of the vagus is specially sensitive 

 to the respiratory quality of the blood. It can hardly 

 be supposed that in the nerve cells of these centres 

 impulses are actually initiated by conditions of the 

 blood supplied to them. . . . But the condition of 

 their blood affects the excitability of ner\e centres; 

 it may be supposed to increase the excitability of those 

 into which embouch the afferent nerves of the gullet 

 and stomach. Some nerve centres are remarkably in- 

 creased in excitability by moderate hunger, just as 

 conversely the knee-jerks are found to be diminished 



"97 



