Developmental changes in activation and effective connectivity in phonological processing

Abstract

The current study examined developmental changes in activation and effective connectivity among brain regions during a phonological processing task, using fMRI. Participants, ages 9-15, were scanned while performing rhyming judgments on pairs of visually presented words. The orthographic and phonological similarity between words in the pair was independently manipulated, so that rhyming judgment could not be based on orthographic similarity. Our results show a developmental increase in activation in the dorsal part of left inferior frontal gyrus (IFG), accompanied by a decrease in the dorsal part of left superior temporal gyrus (STG). The coupling of dorsal IFG with other selected brain regions involved in the phonological decision increased with age, while the coupling of STG decreased with age. These results suggest that during development there is a shift from reliance on sensory auditory representations to reliance on phonological segmentation and covert articulation for performing rhyming judgment on visually presented words. In addition, we found a developmental increase in activation in left posterior parietal cortex that was not accompanied by a change in its connectivity with the other regions. These results suggest that maturational changes within a cortical region are not necessarily accompanied by an increase in its interactions with other regions and its contribution to the task. Our results are consistent with the idea that there is reduced reliance on primary sensory processes as task-relevant processes mature and become more efficient during development.

Fig. 1

Correlation of performance in the scanner in the rhyming task with age of participants. (a) Accuracy and (b) reaction time are presented.

Fig. 2

Regions of activation in the rhyming (red) and perceptual (blue) tasks, and their overlap (purple). Activation is displayed at the threshold of uncorrected p<0.0001.

Fig. 3

Regions showing age-related changes in activation for the rhyming task when linear effects of accuracy are controlled. Red—increased activation with age; blue—decreased activation with age. Plots show the correlation of signal intensity (y axis) and age in months (x axis) in each region. IFG—inferior frontal gyrus (−54, 9, 33), IPS—intraparietal sulcus (−36, −54, 54), STG—superior temporal gyrus (−51, −9, −3), SMG—supramarginal gyrus (−57, −27, 18), MFG—middle frontal gyrus (−39, −6, 51). BA—Brodmann area.

Fig. 4

Developmental increase in activation in the rhyming task (red) overlaid on other maps (blue). (a) Blue=conflicting vs. non-conflicting in inferior frontal gyrus (BA9; displayed at the threshold of uncorrected p<0.0001); (b) blue=correlation between the differential activation for conflicting (compared to non-conflicting conditions) and accuracy in conflicting conditions in intraparietal sulcus (BA 40) and (c) blue=the developmental increase in activation in perceptual condition in middle frontal gyrus (BA 6). Overlap is always purple.

Fig. 5

Correlation with age in bilinear effects (controlled for accuracy). Boxed regions—regions showing correlation of activation with age in conventional analysis. Black arrows—significant main effect of age; grey—non-significant correlations with age; star—significant correlation with age when calculated separately for each bilinear effect. d—Dorsal, v—ventral, a—anterior, IFG—inferior frontal gyrus, STG—superior temporal gyrus, LTC—lateral temporal cortex, IPS—intraparietal sulcus.