Neurobiological basis of family relationship
Toward a Behavioral Neuroscience of Parenting
○Marc H. Bornstein1, Gianluca Esposito2, Nicola DePisapia3, Paola Venuti3
National Inst. Child Health and Human Development, NIH, USA1, RIKEN Brain Science Institute2, University of Trento, Italy3

Infant cry is an emotionally salient and evolutionarily significant stimulus. In this talk, we discuss different prominent modes of human adults' behavioral responses to infant cry, their analysis, and their prevalence across multiple cultures. We then turn to investigations of neural supports for such responses. These studies contrast cries of typically developing infants as well as infants later diagnosed as falling on the autistic spectrum and distinguish preferential neural responses of females and males.
Evolution of life history and origin of human family

○Juichi Yamagiwa1
Graduate School of Science, Kyoto University1

Primates show slow life history traits, such as small litter size, long gestation, long lactation, and long life span, in spite of striking contrasts in habitats, diet, mobility and range size between them. Recent arguments have proposed determinant factors of slow life history in primates, such as large brain size, high risk of juvenile mortality and arboreal life style, but no single factor seems to fully explain it.
Among primates, the great apes (orangutans, gorillas and chimpanzees), in which females have the common feature of starting reproduction after leaving their natal groups, have the slowest life history. Male mating tactics may influence the life history of the great apes in different ways. Female dispersal and independent reproduction from related conspecifics may enable them to form various social structures and flexible life history traits according to male mating strategies. Ecological factors basically shape the gregariousness of females in female-dispersal species, but they can choose from a wide variety of feeding strategies, from individual dispersal to moving in cohesive groups. Males also take various mating tactics according to female movement and association patterns, which in turn also vary with male associations and mating strategies. Although the influences of these ecological and social factors on life history of great apes are different between genera, between species, and between populations, the solitary nature may urge females to choose a slower life history, while stable associations between males and females may promote a faster life history. Frugivorous orangutans and chimpanzees may suffer more costs of female dispersal through decreased foraging efficiency than folivorous gorillas, and chimpanzees with fission-fusion grouping may suffer more social stress than gorillas in highly cohesive groups. Such differences may generally shape the fast-slow continuum of life history in female-dispersal primate species.
Based on these arguments, Modern humans have very unique life history features in comparison with the great apes, such as early weaning, slow maturation and long life span after menopause. The key factors influencing these features are 1) high predation pressure leading to high mortality of immature, 2) encephalization, and 3) formation of human family. Departure from tropical rain forests and expansion of range into arid areas at the end of Miocene should have brought human ancestors high risks of predation by larger carnivores. In order to compensate the loss of immature, human ancestors should have increased fecundity by reduction of inter-birth interval. Early weaning was one of the best tactics to solve these problems. Human brain started to increase its size about 2 million years ago. However, mothers could not be delivered of an infant with large brain, due to the constraints of bipedal walk. Human brain develops slowly and in three different stages in order to achieve large size. This process needs large energy and prevents somatic development until puberty. The adolescent spurt in development of body is unique to humans and it needs various supports by elder generations. These evolutionary histories may have resulted in formation of human family having many dependent immature. Human society is characterized by deep structure of extended kinship. Encephalization has occurred as the social brain to increase social intelligence, which enabled humans to manage different social disciplines of family and community.
Neural basis of family love

○Kazuyuki Shinohara1
Nagasaki University, Medical School1

Neural substrates for parent-child bonding / attachment in humans have not been clarified. We examined patterns of prefrontal cortex (PFC) activity in mothers and fathers or in children while they are watching their own child or parent video clip. We performed near-infrared spectroscopy (NIRS) measurements while mothers and fathers (or children) viewed silent video clips of their own child (or parent) facial expressions and other age-matched child's (or adult's) facial expressions. Children participated in the present study are boys before, during and after puberty. We found that the right ventromedial PFC (vmPFC) was activated in mothers whereas any region of the PFC was not activated in fathers during viewing the smiling facial expression of their own child. However, when fathers were divided into two groups according to AVPR1A polymorphisms, the left vmPFC activation was observed in fathers without the 334 allele of the RS3 but not in fathers with the allele. On the other hand, boys before puberty showed an increase in the right vmPFC activity whereas boys during puberty showed increases in the left vmPFC and dorsolateral PFC activity during watching their own parent smiling. However, boys after puberty did not show any increase in PFC activity. These results suggest that an important role of vmPFC in both maternal and paternal bonding and sexual laterality of neural substrates for parental bonding although all fathers do not always respond to child' smile. Furthermore, neural substrates for attachment may vary through the pubertal development.
Neural basis of the behavioral choice between parenting and infanticide in mice

○黒田公美1, 恒岡洋右1, 刀川夏詩子1
○Kumi O. Kuroda1, Yousuke Tsuneoka1, Kashiko Tachikawa1
理化学研究所 脳科学総合研究センター 黒田研究ユニット1
Unit for Affiliative Social Behavior, RIKEN Brain Science Institute1

Parental care is crucial for survival and proper development of young mammals. Parents are equipped with innate motivation to nurture the young by nursing, cleaning, nest building, and retrieving. However there are other types of pup-directed behaviors: postpartum female mice may sacrifice an unhealthy pup for the sake of healthy littermates, or may abandon the whole litter under adverse conditions. Virgin male mice are spontaneously infanticidal (kill pups). However, when they become fathers by mating and cohabitation with the pregnant female, they provide extensive parental care even toward unfamiliar pups. A similar behavioral transition from infanticide to parenting following mating has been observed in males of many other species including lions and monkeys. Both infanticide in virgin males and parenting in fathers are adaptive reproductive strategy and increases the male's inclusive fitness. Therefore the behavioral choice that an animal makes toward the pups is context-dependent. However the underlying brain mechanism of this decision-making among different pup-directed behaviors remains to be clarified.
To address this question, we investigated the brain areas activated during parenting and infanticide, using c-Fos expression mapping on serial brain sections. We found that specific subregions of the medial preoptic area (MPOA), the bed nucleus of stria terminalis (BNST) and the accessory olfactory bulb were activated during parenting and infanticide, respectively. We examined the roles of these brain areas in pup-directed behaviors by surgical lesion analyses. We showed that an excitotoxic lesion of the central part of the MPOA turned maternal females infanticidal. Additionally, blocking sensory input into the accessory olfactory bulb by eliminating the vomeronasal organ turned male infanticidal behavior into parenting. The possible circuit mechanism of this bistable, flip-flop type of decision making will be discussed.
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