Keiko K. Fujisawa

Reciprocity of prosocial behavior in Japanese preschool children

This study investigated the reciprocity of prosocial behavior among 3- and 4-year-old Japanese preschool children during free-play time. Matrix correlation tests revealed positive correlations between the frequencies of object offering given and received within dyads and between the frequencies of helping given and received within dyads. These results suggest that young children reciprocate prosocial behavior spontaneously. Positive correlations were also found between the frequencies of object offering and helping behavior exchanged within dyads, suggesting that children exchanged the two types of prosocial behaviors (i.e., “interchanged”). The interchange was independent of both reciprocity within object offering and reciprocity within helping behavior in 4-year-olds. Friends reciprocated object offerings more frequently than non-friends, suggesting that friendship affects the quantitative aspect of reciprocity. These data provide refined evidence of reciprocity among children and also suggest that reciprocity becomes more complicated as children grow older.

The Tokyo Twin Cohort Project: Overview and initial findings

The Tokyo Twin Cohort Project (ToTCoP) is a large-scale longitudinal study of 5 years based on 1619 pairs of infant twins reared together. The purpose of the study is to construct a population-based twin registry in Japan and to investigate human growth and development and twin themselves. It covers behavioral, neurological, physical and environmental variables measured by questionnaire, home visiting and brain imaging technology. The full registry contains over 47,000 multiple births collected from the Basic Resident Register, and the targeted population is 3070 probable twins of 0 to 2 years old. Preliminary analysis of the entry questionnaire data showed no serious sampling biases. Descriptive statistics of parental characteristics (parental age, gestation age, parity and placentation, maternal weight, parenting stress) and childrens characteristics (body size at birth, 4 and 10 months of age, milk consumption, and sleeping and social behavior) and their correlations, genetic and environmental contributions and correlations are reported.

Bidirectional influences between maternal parenting and children's peer problems: a longitudinal monozygotic twin difference study.

This twin study examined the bidirectional relationship between maternal parenting behaviors and childrens peer problems that were not confounded by genetic and family environmental factors. Mothers of 259 monozygotic twin pairs reported parenting behaviors and peer problems when twins were 42 and 48 months. Path analyses on monozygotic twin difference scores revealed that authoritative parenting (the presence of consistent discipline and lack of harsh parenting) and peer problems simultaneously influenced each other. Authoritative parenting reduced peer problems, and peer problems increased authoritative parenting. Neither consistent discipline nor harsh parenting alone was associated with peer problems. These results suggest that maternal authoritative parenting works protectively in regard to childrens peer problems, and peer problems can evoke such effective parenting.

Hyperactivity/inattention problems moderate environmental but not genetic mediation between negative parenting and conduct problems.

This study investigated the association between negative parenting (NP) and conduct problems (CP) in 6-year-old twins, taking into account the severity of hyperactivity/inattention problems (HIAP). Analyses of the data from 1,677 pairs of twins and their parents revealed that the shared environmental covariance between NP and CP was moderated by the level of HIAP but not by CP or NP, where the shared environmental covariance was larger in children with higher levels of HIAP than in children with lower levels of HIAP. The genetic covariance between NP and CP was not moderated by the level of HIAP, whereas it was larger in the group with lower levels of CP and NP than in the group with higher levels. These results suggest that severe HIAP strengthens shared environmental associations between NP and CP and that interventions focusing on the shared environmental component of NP would be effective for parents and children with severe HIAP.

Two cohort and three independent anonymous twin projects at the Keio Twin Research Center (KoTReC)

The Keio Twin Research Center has conducted two longitudinal twin cohort projects and has collected three independent and anonymous twin data sets for studies of phenotypes related to psychological, socio-economic, and mental health factors. The Keio Twin Study has examined adolescent and adult cohorts, with a total of over 2,400 pairs of twins and their parents. DNA samples are available for approximately 600 of these twin pairs. The Tokyo Twin Cohort Project has followed a total of 1,600 twin pairs from infancy to early childhood. The large-scale cross-sectional twin study (CROSS) has collected data from over 4,000 twin pairs, from 3 to 26 years of age, and from two high school twin cohorts containing a total of 1,000 pairs of twins. These data sets of anonymous twin studies have mainly targeted academic performance, attitude, and social environment. The present article introduces the research designs and major findings of our center, such as genetic structures of cognitive abilities, personality traits, and academic performances, developmental effects of genes and environment on attitude, socio-cognitive ability and parenting, genes x environment interaction on attitude and conduct problem, and statistical methodological challenges and so on. We discuss the challenges in conducting twin research in Japan.

The Effects of Sibling Relationships on Social Adjustment Among Japanese Twins Compared With Singletons

This study examined the link between sibling relationships and childrens social adjustment by comparing twin siblings and siblings with different ages (singleton siblings}, and clarified the role of reciprocity in sibling relationships on childrens social development. Mothers of 58 monozygotic twin pairs, 48 dizygotic twin pairs, and 86 singleton sibling pairs reported their childrens sibling relationships and social adjustment.This study showed that the effects of sibling relationships on the prosocial behaviors and conduct problems of each child are stronger for twins than for singleton siblings. Moreover, positivity toward ones sibling increased peer problems only among monozygotic twins. The opposite tendency was present among dizygotic twins and singleton siblings. This study suggests the importance for childrens social development of having many interactions with siblings and establishing reciprocity in sibling relationships. Moreover, our results suggest that the quality of sibling relationships among monozygotic twins may be different from those among dizygotic twins and singleton siblings.

Social network analyses of positive and negative relationships among Japanese preschool classmates

Using social network analysis, we investigated the characteristics of social networks composed of positive relationships (positive network: PN) and negative relationships (negative network: NN) in classrooms of Japanese 3- and 4-year-olds. Analysis of “density” showed that PNs were denser than NNs among 4-year-olds but that this was not the case among 3-year-olds. The difference between the probability of dyads of girls forming cliques, between PNs and NNs, was larger than that for dyads of boys or mixed-sex dyads. Four-year-olds formed cliques more often in PNs than in NNs, compared to 3-year-olds. This study showed that both sex combination of dyads and age affect the quantified properties of social networks among preschoolers.

Genetic and environmental relationships between head circumference growth in the first year of life and sociocognitive development in the second year: a longitudinal twin study.

Although growth in head circumference (HC) during infancy is known to predict later childhood outcomes, the mechanisms underlying this association with later sociocognitive abilities remain undetermined. Thus, using a sample of 241 pairs of normally developing Japanese twins, this study investigated the underpinnings of the association between HC growth (difference between HC at birth and at 10 months) and sociocognitive abilities at 19 months as measured by 10 items from the M-CHAT. Phenotypic correlations between HC at birth and sociocognitive abilities and between HC growth and sociocognitive abilities were marginal and not significant. However, multivariate genetic analyses using Cholesky decomposition revealed that genetic influences on HC growth and those on sociocognitive abilities were negatively associated. On the other hand, shared and nonshared environmental influences on HC growth were positively associated with influences on sociocognitive abilities. Genetic and environmental influences on HC at birth were not significantly associated with influences on sociocognitive abilities. These results help to clarify the role of brain growth during infancy in the subsequent development of sociocognitive abilities and highlight the importance of examining the different roles of genetic and environmental influences in studies of these areas.

Changes in genetic and environmental influences on cognitive ability, executive function, and preacademic skills in Japanese preschool age twins.

Identifying the cognitive capacities associated with the development of school readiness is indispensable to support children’s successful school transition. It has been shown that executive function (EF) in preschoolers is associated with both concurrent preacademic and subsequent academic skills. However, most research has controlled for the effect of general cognitive ability (GCA), and little research has examined non-English speaking children, which hinders the understanding of the development of school readiness in culturally diverse contexts. In addition, behavioral genetic research on the genetic and environmental influences on this association has been conducted with school-age children. Thus, the genetic and environmental influences on associations between GCA, EF, and preacademic skills during preschool age are unknown. We conducted multivariate behavioral genetic analyses on two waves of longitudinal data at 42 and 60 months of age from 171 and 135 pairs of monozygotic and dizygotic Japanese twins. The findings suggested that a genetic factor influenced GCA at 42 months and mediated preacademic ability at 60 months. In addition, another genetic factor emerged by 60 months that genetically mediated EF and math ability, independent of GCA. Preacademic ability at 60 months was affected by shared environments that influenced EF, rather than GCA, at 42 months. Moreover, shared environments that influenced preacademic ability at 42 months affected later GCA at 60 months. Finally, nonshared environments that had emerged by 60 months mediated these relationships, though the magnitude of this effect was modest.