1344 



HORMONAL REGULATION OF BEHAVIOR 



which could induce a new cycle of court- 

 ship and nest-building. Thus, the succession 

 of changes in behavior patterns which char- 

 acterizes the breeding cycle depends partly 

 on changes in hormone secretion which are 

 in turn partially stimulated by the changing 

 conditions of the environment (Lehrman, 

 1959a, b). 



In mammals, the ability of stimuli i)ro- 

 vided by the young to induce the main- 

 tenance of lactation, and to suppress the 

 recurrence of estrus, further indicates that 

 the changing pattern of the behavior of the 

 mother is kept appropriate to the external 

 situation partly through the fact that the 

 endocrine changes which influence her be- 

 havior are themselves capable of being in- 

 fluenced by the external situation. 



The readiness with which milk ejection 

 can be conditioned poses a number of prob- 

 lems of special interest in connection with 

 the development of mother-young relation- 

 ships in mammals. If the sensations of ten- 

 sion arising from mammary engorgement 

 play a role, as has been suggested, in the 

 motivation of maternal nursing behavior, it 

 must be borne in mind that the milk-ejec- 

 tion response is itself an increase in tension 

 in the mammary glands. Since young ani- 

 mals characteristically become active just 

 before and during the time when they are 

 fed, it seems likely that changes in intra- 

 mammary tension will occur as conditioned 

 responses to the sights and sounds char- 

 acteristic of the young. The occurrence of 

 such conditioned responses, their manner 

 of formation, and the contribution they 

 make to the maintenance of mother-young 

 relationships are all problems which should 

 be most rewarding to the investigator who 

 attacks them. 



Both in birds and in mammals, tlie estab- 

 lishment and maintenance of relations be- 

 tween the parent and the young (or eggs) 

 is a process, or series of processes, of great 

 complexity, involving a reciprocal interac- 

 tion between, on the one hand, hormonal 

 effects on behavior, and on the other, the 

 effects of external stimuli (including those 

 arising from the behavior of the animal and 

 of its species-mates) on the patterns of hor- 

 mone secretion. 



C. MECHANISMS OF HORMONAL ACTION 

 ON BEHAVIOR 



1. Formulation of the Problem 



The interpretation of the manner in which 

 hormones infiuence behavior patterns is 

 an extremely complex problem. As Beach 

 (1948j has pointed out, and as must be 

 apparent from much of the data presented 

 in earlier' sections of this chapter, a be- 

 havioral response does not typically depend 

 on one and only one hormone, nor is any 

 hormone known which produces one and 

 only one effect on the organism. However, 

 when we know that a hormone has an in- 

 fluence on the development or occurrence 

 of a behavior pattern, we may usefully ask 

 which of the various organic effects the hor- 

 mone is known to have are relevant to its 

 effect on the behavior pattern, and whether 

 additional organic effects must be assumed 

 in order to explain the fact that the hor- 

 mone has the observed effect on the be- 

 havior. 



Hormones may influence behavior pat- 

 terns through either peripheral or central 

 effects. By "peripheral" effects, I mean that 

 the hormone may change the animal's be- 

 havior by causing changes in structures or 

 processes external to the central nervous 

 system, which changes in turn result in 

 alterations in the pattern of afferent inflow. 

 Such changes may consist of grow^th changes 

 in structures used in the behavior (Lehr- 

 man, 1955) , of changes in vascularity which 

 influence the conditions of tension in the 

 tissues concerned (Clark and Birch, 1946; 

 Birch and Clark, 1946, 1950) , of changes in 

 sensitivity of a sensory surface (Freud 

 and Uyldert, 1948b; Schneider, Costiloe, 

 Howard and Wolf, 1958), of the develop- 

 ment of sensitive structures (Beach and 

 Levinson, 1950) , etc. 



By "central" effects, I mean that a hor- 

 mone may influence the animal's behavior 

 by a direct effect on structures of the cen- 

 tral nervous system which are in some way 

 involved in the organization and production 

 of the behavior. Such effects may be rela- 

 tively unspecific excitatory effects influenc- 

 ing "arousal" systems such as the reticular 

 activating system (Magoun, 1952a, b; Dell, 



