PARENTAL BEHAVIOR 



1339 



some generalized learning about the en- 

 vironment which occurs during early life 

 may participate in the organization of 

 maternal behavior. 



Stamm (1955) found that lesions in the 

 median cerebral cortex caused more dis- 

 turbance in the maternal behavior of rats 

 than did lesions of similar size elsewhere 

 on the cortical surface. Rats so treated 

 licked their young and severed the um- 

 bilical cords, but did not retrieve the litters 

 together into a nest after parturition and 

 did not permit the young to suckle. How- 

 ever, introduction of foster pups with pre- 

 A'ious suckling experience markedly changed 

 tlie behavior of the operated mothers. The 

 foster pups, by hanging onto the nipples of 

 the mother rats, induced lactation, and the 

 operated animals subsequently hovered over 

 the litters, permitting the young to nurse; 

 they then collected and retrieved the pups, 

 which survived. These observations may in- 

 dicate that the cortical lesion did not inter- 

 fere with the ability to carry out the ma- 

 ternal behavior, but perhaps reduced the 

 impact of the stimulation which normally 

 elicits this behavior. 



Interaction of hormonal and experien- 

 tial INFLUENCES. Froiii the foregoing dis- 

 cussion, it is apparent that some behavior 

 patterns are simultaneously influenced by 

 various endocrine conditions and by pre- 

 vious experience. This fact raises some in- 

 teresting problems concerned with the inter- 

 relations of such influences. 



Uyldert (1946) allowed 35 primiparous 

 rats to deliver their young on a floor made 

 of wide-mesh wire screen, through which 

 the newborn pups fell, so that the mother 

 had no contact with them. Animals of a 

 control group were allowed to retain their 

 young and to nurse them normally. After 

 the young of the control group were weaned, 

 both groups were allowed to rest for several 

 weeks, following which each animal was in- 

 jected with 200 fjig. of estrone per day for 

 20 days, which induced mammary develop- 

 ment. One day after the cessation of this 

 treatment, rats of both groups were pro- 

 vided with newborn young. Eight of the 9 

 control animals (animals with previous nor- 

 mal nursing experience) reared from 5 to 

 8 young each; only 12 of the 35 experi- 

 mental animals (animals with no previous 



experience of nursing young) succeeded in 

 rearing young, and these reared only from 

 1 to 3 young each. Of the control animals 

 56 per cent kept all their young alive, com- 

 pared with 11 per cent of the experimental 

 animals. Clearly, the previous experience 

 of nursing and rearing the young had an 

 effect on the animals' response to the com- 

 bination of estrone treatment and stimuli 

 from the young. Observations are lacking, 

 however, that would indicate whether the 

 difference between the experimental and 

 control groups resided in the animals' re- 

 sponsiveness to suckling stimulation, or in 

 their behavior toward the young, which 

 might determine whether suckling could 

 take place or not. 



Riddle, Lahr and Bates (1935a, b, c, 

 1952) , reported that some virgin rats show 

 retrieving behavior in response to prolactin 

 injection. They stated that the care of the 

 young shown by such animals is not equiva- 

 lent to that usually seen in multiparous rats, 

 but they did not make a comparison of 

 the effects of the hormone injection on the 

 behavior of virgin and of experienced rats. 

 Loisel (1906) found that a bitch which be- 

 gan to lactate after a pseudopregnancy 

 accepted three young rabbits which were 

 placed with her, licked them, and facilitated 

 their approach to her nipples (they could 

 not suckle). This animal had never seen 

 young before. Fisher (1956) found that 

 a testosterone salt injected locally into the 

 hypothalamus induced intense nest-build- 

 ing and retrieving behavior in some male 

 rats. These animals were presumably quite 

 inexperienced. 



In connection with studies of mammalian 

 parental behavior, it is unfortunate that no 

 use has been made of the technique of com- 

 paring behavior elicited by hormone treat- 

 ment in animals without previous experi- 

 ence with that elicited from animals with 

 various amounts and kinds of previous ex- 

 perience. Such a technique has been ex- 

 tremely valuable in studies of sexual be- 

 havior. As I have pointed out, comparison 

 of parental behavior at first and at later 

 breeding episodes may not reveal the role 

 of experiential factors in the changing pat- 

 tern of behavior during each episode. This 

 is sometimes because the experience of the 

 animals during an early phase of the cycle 



