Beyond the average brain: individual differences in social brain development are associated with friendship quality

Abstract

We tested whether adolescents differ from each other in the structural development of the social brain and whether individual differences in social brain development predicted variability in friendship quality development. Adolescents (N = 299, Mage T1 = 13.98 years) were followed across three biannual waves. We analysed self-reported friendship quality with the best friend at T1 and T3, and bilateral measures of surface area and cortical thickness of the medial prefrontal cortex (mPFC), posterior superior temporal sulcus (pSTS), temporoparietal junction (TPJ) and precuneus across all waves. At the group level, growth curve models confirmed non-linear decreases of surface area and cortical thickness in social brain regions. We identified substantial individual differences in levels and change rates of social brain regions, especially for surface area of the mPFC, pSTS and TPJ. Change rates of cortical thickness varied less between persons. Higher levels of mPFC surface area and cortical thickness predicted stronger increases in friendship quality over time. Moreover, faster cortical thinning of mPFC surface area predicted a stronger increase in friendship quality. Higher levels of TPJ cortical thickness predicted lower friendship quality. Together, our results indicate heterogeneity in social brain development and how this variability uniquely predicts friendship quality development.

Keywords: adolescence; friendship quality; longitudinal; social brain; structural brain development.

Fig. 1.

(A) Example of a latent growth curve model including an intercept, linear slope and quadratic slope to model the development of mPFC area across three waves. (B) Intercept, linear and quadratic slope of mPFC surface area predicting changes in friendship quality over time. mPFC = medial prefrontal cortex.

Fig. 2.

Observed individual trajectories for each region of interest. mPFC = medial prefrontal cortex; pSTS = posterior superior temporal sulcus; TPJ = temporoparietal junction. Estimated population trajectories for each gender are shown by coloured lines. If no gender differences were present, we plotted the average developmental trajectory across gender in solid black lines. The shaded areas represent the 95% confidence intervals.