Earlier specialization, but not connectivity, predicts longitudinal changes in phonological and semantic specialization in 7- to 9-year-old children

A central assumption of the Interactive Specialization model 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-year of age was 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. Unexpectedly, we found no evidence that earlier connectivity at age 7 predicted later specialization at age 9, therefore, not supporting the assumption of the Interactive Specialization model. However, we 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. This different predictive effect may be due to the earlier maturation of semantic processing, as additional analyses showed greater semantic than phonological specialization, coupled with less connectivity for the semantic compared to phonological processing, at age 7. Overall, this study shows that earlier specialization, but not connectivity, is associated with later specialization in the language domain, suggesting a need for modifications in models of brain development. In addition, this finding may indicate that linguistic specialization rather than interaction should be the focus when it comes to early identification and intervention of children with low language skills.