Age-Related Changes in E/I Balance Estimated With Hurst Exponent and Links With Developmental Skills in Preschool Children.

Cortical excitation-inhibition (E/I) balance regulates sensitive periods of plasticity and is critical for brain development. Yet, neuroimaging studies characterizing E/I dynamics in early childhood are rare. The Hurst exponent (H), derived from resting-state functional magnetic resonance imaging (rs-fMRI), provides a noninvasive proxy for E/I balance. We investigated age-related changes in H using longitudinal rs-fMRI from 55 typically developing children aged 1.5-5 years (78 sessions during natural sleep). Linear mixed-effects models revealed significant age-related increases in H, signifying greater inhibition or more balanced E/I, in three right-hemisphere regions: inferior frontal gyrus (IFG) pars opercularis and triangularis, and middle temporal pole. Whole-brain maps showed positive age effects across most cortical areas, though the most robust increases occurred in higher order association cortices rather than primary sensory regions, consistent with hierarchical network maturation. Higher H in right IFG opercular was associated with better expressive language skills and fewer behavioral/emotional problems, controlling for age and sex. These findings suggest that E/I balance maturation during toddlerhood and preschool years is most pronounced in regions supporting language development and cognitive control. Our results characterized normative developmental trajectories of H during an important neurodevelopmental window and its associations with emerging behavioral competencies, potentially informing future investigations of atypical E/I maturation in neurodevelopmental disorders.