Same ages, different stages: Pubertal development in 9- and 10-year olds is associated with entropy of fMRI signals.

Entropy is a novel brain measure that holds important information about brain flexibility and functioning, with promise for informing brain development in adolescence, as it has been shown to change across the lifespan. However, little is known about how it changes during the critically important phase of pubertal development, which kickstarts a period of broad neural reorganization and restructuring. This proof-of-concept cross-sectional study examined associations between fMRI signal entropy and early pubertal development in a large, diverse sample of children. Data (N = 6838; 49.6% male; ages 8.92-11.08) was drawn from the first wave of the Adolescent Brain Cognitive Development study. Sample entropy was calculated on the time series of the resting-state fMRI signals for every grayordinate (i.e., cortical vertex and subcortical voxel). Parent-reported pubertal development (approximated Tanner stage) and salivary hormone levels (dehydroepiandrosterone; estradiol; testosterone) were correlated with sample entropy across the whole brain. The patterns of association between sample entropy and pubertal stage/hormone levels were inspected for males and females separately. Findings indicated pubertal development was associated with higher levels of resting state fMRI signal entropy, specifically in the occipital, parietal, and temporal lobes. Associations were apparent in females across most pubertal metrics. For males the constrained range of pubertal development may in part account for weaker associations observed. Further, adjustment for variables associated with early timing of pubertal development (socioeconomic status, body mass index) reduced the strength of puberty-entropy associations for both sexes. Longitudinal research is needed to confirm the associations between sample entropy and puberty, to evaluate whether stronger associations emerge as more males enter puberty in earnest, and to disentangle potential confounds.