Functional brain network community structure in childhood: Unfinished territories and fuzzy boundaries

Adult cortex is organized into distributed functional communities. Yet, little is known about community architecture in childhood. Here, we address this gap by studying the community structure of cortex in 670 children aged 9-11 years from the Adolescent Brain and Cognitive Development study. Using fMRI, we first applied a data-driven partitioning algorithm to assign regions to communities, then used a model-based algorithm to further probe community interactions. Children showed similar community structure to adults in early-developing sensory and motor communities. Differences emerged in transmodal areas, manifesting in expanded limbic territory and more flexible interactions between association regions in children relative to adults. The greatest uncertainty in algorithmic assignment was localized to areas supporting attention, indicating complex undifferentiated connectivity patterns in these regions. Collectively, our findings suggest that community boundaries are not solidified in middle childhood, an instability that provides important context for children’s thoughts and behaviors during this period.