Executive functioning in adolescence: Developmental trajectories and longitudinal links to sleep and neural indicators

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Cognitive abilities change dramatically over the course of adolescence, especially the neurocognitive processes related to executive functioning (EF). EF consists of a set of higher-order cognitive skills that are recruited when individuals face cognitively challenging situations, and is centrally involved in attention regulation, information processing and updating, and problem solving. EF is considered to be a central indicator of neurocognition in adolescence and depends heavily on neural networks involving notably the prefrontal cortex, which undergoes significant developments throughout childhood and adolescence. These neurodevelopments include myelination of axons and synaptic pruning, resulting in increased efficiency in the neural circuits that subsume EF. As a result, age-related improvements in neurocognition throughout adolescence are expected. Indeed, age differences in EF are often observed, with older adolescents outperforming their younger counterparts on a variety of executive tasks. These mean-level differences between age groups are generally interpreted as reflecting developmental improvements - yet, cross-sectional studies cannot speak to cognitive development per se. Cross-sectional studies rely on comparisons of groups of adolescents of different ages, and thus cannot disentangle age effects from any other characteristic that may distinguish the age groups (cohort effects). In contrast, longitudinal designs with at least three time points facilitate the disaggregation of age and cohort effects, as well as the characterization of cognitive development on two levels: the pattern of change within each individual and differences between individuals in this within-person change. Thus, longitudinal designs with three time points or more are essential for answering key questions about neurocognitive development, pertaining for instance to the rate and shape (e.g., linear or quadratic) of EF improvements throughout adolescence and individual differences in these patterns. Although progression in neurocognitive capacity happens at the within-person level by definition, all EF research with adolescents to date has involved the analysis of strictly between-person data, or has relied on only two assessment points. As a result, current knowledge on the rhythm and shape of executive improvement in adolescence is limited. This, in turn, constrains the state of knowledge on all other questions pertaining to the process of EF development, such as the nature of the links between this process and neurobiological underpinnings presumed to be of key importance, such as sleep patterns or brain anatomy and connectivity. Aiming to address these gaps, this program of longitudinal research consists of four studies seeking to characterize the rhythm and shape of age-related improvements in EF in adolescence, and examine the associations between these improvement trajectories and adolescents' brain structure, function, and their sleep patterns.