Modality-specific and -independent developmental differences in the neural substrate for lexical processing
The neuroanatomy of developmental differences in lexical processing was examined with functional magnetic resonance imaging (fMRI) in 15 adults and 15 children. We examined modality specific and modality independent (auditory and visual presentation) patterns of brain activation during spelling, rhyming and meaning judgment tasks. A direct comparison of the modalities revealed that adults showed a large area of activation in the fusiform gyrus for visual word forms and in the superior temporal gyrus for auditory word forms. In contrast, the modality comparison for children revealed no activation in the fusiform gyrus for visual word forms and modest activation in the superior temporal gyrus for auditory word forms. There were also modality independent developmental differences with adults showing more activation than children in the inferior frontal gyrus for the spelling, rhyming and meaning tasks. These results suggest that development is characterized by increasing involvement of the inferior frontal gyrus in lexical processing and by the specialization of unimodal regions for visual and auditory word forms.