| Summary: | The period of life between puberty and adulthood, adolescence, has perplexed adults for millennia. Adolescence is marked by significant physical, cognitive, and social changes. Social lives become more complex during adolescence, and the teenage years are when we hone our skills at navigating the social world. The aim of my thesis was to examine brain development and social interactions during the period of adolescence. I conducted three brain imaging experiments to investigate typical developmental trajectories of brain structure between childhood and adulthood. These three studies used a large longitudinal dataset and mixed-effects modelling in order to account for individual differences. My first study found evidence that intracranial volume continues to develop through the second decade, and describes the consequences of intracranial volume correction procedures on developmental studies. The second study provided evidence for the hypothesis that subcortical brain regions involved in processing affect and reward structurally mature before prefrontal cortical regions involved in cognitive control to varying degrees across individuals. The third study found evidence for continued structural development regions of the brain involved in understanding other people between late childhood to early adulthood. My behavioural experiment showed that keeping track of non-social information impacts the ability to navigate social interactions in adolescents and adults. In addition to these four empirical studies, I conducted three reviews to synthesise and update our understanding of a) adolescence as a potential sensitive period for social learning, b) what longitudinal structural brain imaging studies can tell us about brain development, and c) the evidence for how using the Internet could impact brain development in adolescence. Overall, my findings shed new light, and challenge current theories, on brain development and social cognition during adolescence.
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