Linking temporal dynamics of children's natural behavior to brain development

Across the school day, children must continually modulate their behavior to be appropriate to the classroom. Such behavioral regulation is effortful and children vary in their ability to sustain behavioral regulation over time. We have previously shown that daily increases in activity levels (DIA) across the school day relate to questionnaire measures of self-control, and that children who show shallower DIA in third grade are more likely to graduate from college. Here, we ask how individual differences in brain development relate to children's ability to sustain behavioral regulation as measured by DIA. We take advantage of neuroimaging and actigraphy data collected in the ABCD study (N = 4338, M_age = 11.95, 15.65 days of actigraphy data per child). We preregistered hypotheses that steeper DIA (lower sustained control) would be associated with thinner cortex, lower surface area, and weaker correlations between the executive control network and somatomotor network. We first replicated typical patterns of DIA, as well as associations between steeper DIA and lower inhibitory control. We then showed that greater DIA is associated with thinner cortex in areas related to executive control (βs = -0.04 to -0.06) and motor action (βs = -0.04 to -0.05). Greater DIA was also associated with lower connectivity between the executive control and somatomotor networks (β = -0.07), and greater connectivity within the somatomotor network (β = 0.12). Our results suggest that DIA is a promising measure of naturalistic self-control that can be used to study between- and within-person variability at scale.