One of the most important social identities that children learn to define themselves and others by is sex, becoming a salient social category by early childhood. Although older children begin to show greater flexibility in their gendered behaviors and attitudes, gender rigidity intensifies again around the time of puberty. In the current study, we assessed behavioral and neural biases to sex across a wide age group. Ninety-three youth (ages 7–17 years) provided behavioral rating of same- and opposite-sex attitudes, and 52 youth (ages 4–18 years) underwent an fMRI scan as they matched the emotion of same- and opposite-sex faces. We demonstrate significant age-related behavioral biases of sex that are mediated by differential amygdala response to opposite-sex relative to same-sex faces in children, an effect that completely attenuates by the teenage years. Moreover, we find a second peak in amygdala sensitivity to opposite-sex faces around the time of puberty. Thus, the amygdala codes for developmentally dependent and motivationally relevant social identification across development.

Neuroimaging research in adults has consistently found that differential perception of race is associated with increased amygdala activity. We hypothesized that such neural biases unlikely reflect innate processes but instead emerge over development. In the current study, we used fMRI to examine the neurodevelopmental trajectory of the amygdala in response to race across childhood and adolescence ranging from 4 to 16 years. Thirty-two youths viewed African American and European American faces during a functional brain scan. Results suggest that differential amygdala response to African American faces does not emerge until adolescence, reflecting the increasing salience of race across development. In addition, greater peer diversity was associated with attenuated amygdala response to African American faces, suggesting that intergroup racial contact may reduce the salience of race.