Earlier connectivity and specialization predict longitudinal changes in phonological and semantic specialization in 7- to 9-year-old children

A central assumption of the Interactive Specialization model (ISM) of brain development postulates that earlier interaction between brain regions (i.e., functional connectivity) drives later specialization. The goal of the current study was to examine this assumption in the language domain. Longitudinal data from 32 children at 7 and 9 years of age were analyzed. The children were given a sound judgment task and a meaning judgment task while undergoing functional magnetic resonance imaging (fMRI) to assess children's phonological and semantic specialization, and functional connectivity in the brain. We found evidence that earlier connectivity at age 7 predicted later specialization at age 9 within the dorsal pathway for phonology and ventral pathway for semantics, therefore supporting the assumption of the Interactive Specialization model. We also found that individual differences in specialization at age 7 predicted later specialization at age 9, and this predictive effect was more pronounced for semantics than phonology. In sum, our results not only suggest a continued development of neural specialization for both phonology and semantics but also support the core hypothesis of ISM as earlier pathway connectivity within dorsal inferior frontal gyrus and posterior superior temporal gyrus appeared as a significant predictor for subsequent phonological specialization, and within ventral inferior frontal gyrus and posterior middle temporal gyrus appeared as a significant predictor for subsequent semantic specialization.