Abstract
Sexually dimorphic brain development and behavior are known to be influenced by sex hormones exposure in prenatal periods. On the other hand, second-to forth digit ratio (2D/4D) has been used as an indirect method to investigate the putative effects of prenatal exposure to androgen. In the present study, we herein investigated the relationship between gender-role play behavior and the second-to-fourth digit ratio (2D/4D), which has been used as an indirect method to investigate the putative effects of prenatal exposure to androgens, in school-aged children. Among 4981 children who became 8 years old by November 2014 and were contactable for this survey by The Hokkaido Study of Environment and Children's Health, 1631 (32.7%), who had data for 2D/4D and Pre-school Activities Inventory (PSAI) as well as data for the survey at baseline, were available for analysis. Parents sent reports of PSAI on the sex-typical characteristics, preferred toys, and play activities of children, and black and white photocopies of the left and right hand palms via mail. PSAI consisted of 12 masculine items and 12 feminine items, and a composite score was created by subtracting the feminine score from the masculine score, with higher scores representing masculine-typical behavior. While composite scores in PSAI were significantly higher in boys than in girls, 2D/4D was significantly lower in boys than in girls. Although the presence or absence of brothers or sisters affected the composite, masculine, and feminine scored of PSAI, a multivariate regression model revealed that 2D/4D negatively correlated with the composite scores of PSAI in boys, whereas no correlation was found in girls. Although 2D/4D negatively correlated with the masculine score in boys and girls, no correlation was observed between 2D/4D and the feminine score. In conclusion, although social factors, such as the existence of brother or sisters, affect dimorphic brain development and behavior in childhood, the present study revealed that the prenatal hormonal environment was an important factor influencing masculine-typical dimorphic brain development and behavior in school-aged children.
Highlights
Sexual dimorphism is characterized by differences in cognitive functions between boys and girls, and has been associated with anatomical and physiological differences in the brain
The present study focused on the hypothesis that sexually dimorphic brain development and behavior are associated with sexual differences in digits, which are affected by the prenatal hormonal environment, androgen exposure
The characteristics of the mothers and their children who were available for analysis in this study were compared to those of other mothers and children who were not available for this analysis in Table 2. second-to-fourth digit ratio (2D/4D) and Pre-school Activities Inventory (PSAI) were both derived from the following participants; older mothers, a higher annual household income, higher
Summary
Sexual dimorphism is characterized by differences in cognitive functions between boys and girls, and has been associated with anatomical and physiological differences in the brain. Dimorphic brain development and behavior are known to be influenced by exposure to sex hormones during prenatal periods. XY-chromosome individuals with complete androgen insensitivity syndrome (CAIS) show fewer male-typical behaviors and more female-typical behaviors despite normally functioning testes with androgen exposure during gestation[7, 8]. These findings have been supported by studies using animals[9,10,11], which revealed that experimental manipulations of hormones during gestation affected the sexual dimorphism of behaviors
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