Developmental disinhibition gates language lateralization in childhood

Hemispheric specialization is a hallmark of brain organization, yet how functionally specialized circuits develop remains unclear. In humans, the developmental shift toward left-hemisphere dominance for language offers a well-characterized model for investigating this question. Here, we built personalized whole-brain neurophysiological models in children and adolescents to simulate task-evoked dynamics from auditory perception to language production. We demonstrate that expressive language lateralization emerges through distinct inhibitory processes. In early childhood, interhemispheric inhibitory asymmetry is present, characterized by stronger projections from left pyramidal neurons to right interneurons, but is insufficient to drive functional specialization. Using in silico manipulations, we show that developmental reduction in local inhibition is necessary to unmask the functional influence of early structural asymmetries. Our findings provide a mechanistic account in which expressive language specialization emerges from the interaction between early structural asymmetry and developmental disinhibition, and offer a generalizable computational framework for studying circuit specialization across species and cognitive domains. Left hemisphere language dominance emerges across childhood. Whole-brain modelling reveals that asymmetric interhemispheric inhibition is initially masked in early development and progressively unmasked with maturation, driving hemispheric specialization.