Developmental Increase in Top–Down and Bottom–Up Processing in a Phonological Task: An Effective Connectivity, fMRI Study

Abstract

Abstract We examined age-related changes in the interactions among brain regions in children performing rhyming judgments on visually presented words. The difficulty of the task was manipulated by including a conflict between task-relevant (phonological) information and task-irrelevant (orthographic) information. The conflicting conditions included pairs of words that rhyme despite having different spelling patterns (jazz–has), or words that do not rhyme despite having similar spelling patterns (pint–mint). These were contrasted with nonconflicting pairs that have similar orthography and phonology (dime–lime) or different orthography and phonology (press–list). Using fMRI, we examined effective connectivity among five left hemisphere regions of interest: fusiform gyrus (FG), inferior frontal gyrus (IFG), intraparietal sulcus (IPS), lateral temporal cortex (LTC), and medial frontal gyrus (MeFG). Age-related increases were observed in the influence of the IFG and FG on the LTC, but only in conflicting conditions. These results reflect a developmental increase in the convergence of bottom–up and top–down information on the LTC. In older children, top–down control process may selectively enhance the sensitivity of the LTC to bottom–up information from the FG. This may be evident especially in situations that require selective enhancement of task-relevant versus task-irrelevant information. Altogether these results provide a direct evidence for a developmental increase in top–down control processes in language processing. The developmental increase in bottom–up processing may be secondary to the enhancement of top–down processes.