PARENTAL BEHAVIOR 



1345 



19o81)), or they may be more si)ecific effects 

 on brain structures involved in the organiza- 

 tion of specific behavior patterns (Fisher, 

 1956; Harris, Michael and Scott, 1958). 



Morgan (1943, 1957, 1959) proposed the 

 concept of "central motive state," by which 

 he means a state of arousal of a center 

 in the central nervous system which, once 

 aroused, persists without outside support 

 from sensory or other input, which pre- 

 disposes the organism to react in certain 

 ways to particular stimuli and not to react 

 to others, and which "emits" specific pat- 

 terns of behavior. This theory is, in many 

 resj)ects, remarkably similar to that of 

 Lorenz (1950) (Beach, 1942; Tinbergen, 

 1951). 



The relevance of Morgan's theory for our 

 problem arises from the fact that he re- 

 gards as an important corollary of the 

 theory the statement that chemical and 

 hormonal conditions of the blood directly 

 activate the central nervous system and in- 

 duce central motive states, and that this 

 is the major way in which hormonal effects 

 are exerted upon behavior. In an earlier 

 discussion (Lehrman, 1956b) , I heavily 

 emphasized the role of peripheral effects 

 of hormones as the means by which they 

 influence behavior, and implied that direct 

 central effects are of little or no imi)ortance. 

 This was in the context of a critical dis- 

 cussion of a theory of behavior which de- 

 pended, at that time, on the assumption of 

 almost exclusively central forms of organi- 

 zation for most major behavior activities. 

 In this context, I believe I unduly under- 

 emphasized the importance of central in- 

 fluences of hormones, and subsequent re- 

 search confirms this view. On the other 

 hand, Morgan's central theory is in part 

 a reaction against the very influential ear- 

 lier theory of Cannon a929, 1934), who 

 believed that most states of motivation de- 

 pend solely or primarily on the perception 

 of the condition of peripheral structures. In 

 this context, I believe that Morgan some- 

 what underemphasized the importance of 

 pt'i'iphcral factors in the (lcvch)pment of 

 motive states. At this point, it does not 

 seem to me to be very profitable to attempt 

 to determine which is in general "more im- 



portant," central or i)eripheral influences, 

 since central and peripheral contributions 

 are undoubtedly both involved in many 

 cases, and are of varying importance in 

 others. I shall attempt to illustrate the ways 

 in which hormones may influence behavior 

 patterns by selecting several patterns of be- 

 havior, including some discussed earlier in 

 this chapter, for a further discussion of the 

 mechanisms involved. 



i2. Examples of Peripheral Contributions to 

 Hormonal Effects on Behavior 



Parental feeding behavior in ring doves. 

 Injection of prolactin into ring doves with 

 previous breeding experience causes them 

 to feed young doves provided by the experi- 

 menter (Lehrman, 1955). Prolactin has 

 many other effects on doves, some of which 

 may be relevant to this behavioral effect. 

 Prolactin causes the crop to become en- 

 gorged with the substance which the Inrds 

 regurgitate to their young (Riddle and 

 Braucher, 1931); it causes a substantial 

 temjiorary overgrowth of the liver and in- 

 testine (Bates, Riddle, Lahr and Schooley, 

 1937) ; it inhibits the secretion of FSH by 

 the pituitary gland (Bates, Riddle and 

 Lahr, 1937) , resulting in the suppression of 

 gonadal activity (Bates, Lahr and Riddle, 

 1935). 



Riddle (1935) assumed that, if this hor- 

 mone influences a behavior pattern, it must 

 be because of some interaction between the 

 hormone and nerve tissue itself. In the case 

 of the behavior we are considering, this is 

 not necessarily so, since some of the effects 

 already enumerated might be adequate to 

 account for the arousal of parental feeding 

 behavior. Lehrman (1955) injected prolac- 

 tin into a group of doves with previous 

 breeding experience and then, before test- 

 ing them for regurgitation-feeding behav- 

 ior toward squabs, anesthetized their crops 

 by injecting a long-acting local anesthetic 

 directly into the crop wall. These birds 

 showed a sharply reduced incidence of re- 

 gurgitation-feeding behavior, and a cor- 

 responding reduction in apparent "parental" 

 interest in the squabs, as compared with a 

 control group in which the same amount of 

 the anesthetic was injected into the skin 



