Developmental increases in effective connectivity to brain regions involved in phonological processing during tasks with orthographic demands.

Developmental differences (9- to 15-year-olds) in effective connectivity in left hemisphere regions were examined using dynamic causal modeling (DCM) of functional magnetic resonance imaging (fMRI) data. Children completed spelling tasks in the visual and auditory modalities in which they were asked to determine if two words were spelled the same from the first vowel onwards. Intrinsic (anatomical) connections were strongest from primary cortical regions to unimodal association areas - from Heschl's gyrus to superior temporal gyrus for the auditory spelling task and from calcarine to fusiform gyrus for the visual spelling task. The modulatory (experimental) effect for the visual spelling task from calcarine to superior temporal gyrus was stronger than all other effects from calcarine and this effect showed a developmental increase, suggesting automatic activation of phonology that increased with age. The modulatory effect from Heschl's gyrus to dorsal inferior frontal gyrus also showed a developmental increase, suggesting age-related increases in phonological segmentation in verbal working memory. All together, these results suggest that there are developmental increases in automatic access into brain regions involved in phonological processing in tasks that require orthographic processing.