Developmental changes in brain regions involved in phonological and orthographic processing during spoken language processing
Developmental differences in brain activation of 9- to 15-year-old children were examined during an auditory rhyme decision task to spoken words using functional magnetic resonance imaging (fMRI). As a group, children showed activation in the left superior/middle temporal gyri (BA 22, 21), right middle temporal gyrus (BA 21), dorsal (BA 45, pars opercularis) and ventral (BA 46, pars triangularis) aspects of the left inferior frontal gyrus, and left fusiform gyrus (BA 37). There was a developmental increase in activation in the left middle temporal gyrus (BA 22) across all lexical conditions, suggesting that automatic semantic processing increases with age regardless of task demands. Activation in the left dorsal inferior frontal gyrus also showed developmental increases for the conflicting (e.g. PINT-MINT) compared to the non-conflicting (e.g. PRESS-LIST) non-rhyming conditions, indicating that this area becomes increasingly involved in strategic phonological processing in the face of conflicting orthographic and phonological representations. Left inferior temporal/fusiform gyrus (BA 37) activation was also greater for the conflicting (e.g. PINT-MINT) condition, and a developmental increase was found in the positive relationship between individuals’ reaction time and activation in the left lingual/fusiform gyrus (BA 18) in this condition, indicating an age-related increase in the association between longer reaction times and greater visual-orthographic processing in this conflicting condition. These results suggest that orthographic processing is automatically engaged by children in a task that does not require access to orthographic information for correct performance, especially when orthographic and phonological representations conflict, and especially for longer response latencies in older children.