Developmental changes in the inferior frontal cortex for selecting semantic representations

Abstract

Functional magnetic resonance imaging (fMRI) was used to examine the neural correlates of semantic judgments to Chinese words in a group of 10-15 year old Chinese children. Two semantic tasks were used: visual-visual versus visual-auditory presentation. The first word was visually presented (i.e. character) and the second word was either visually or auditorily presented, and the participant had to determine if these two words were related in meaning. Different from English, Chinese has many homophones in which each spoken word corresponds to many characters. The visual-auditory task, therefore, required greater engagement of cognitive control for the participants to select a semantically appropriate answer for the second homophonic word. Weaker association pairs produced greater activation in the mid-ventral region of left inferior frontal gyrus (BA 45) for both tasks. However, this effect was stronger for the visual-auditory task than for the visual-visual task and this difference was stronger for older compared to younger children. The findings suggest greater involvement of semantic selection mechanisms in the cross-modal task requiring the access of the appropriate meaning of homophonic spoken words, especially for older children.

Keywords: Age; Association strength; Auditory; Semantic; Visual; fMRI.

Fig. 1

Effects of association strength in the visual–visual semantic judgment task: (a) stronger association produced greater activation for related pairs in the posterior region of left inferior parietal lobule (IPL, BA 39); (b) weaker association produced greater activation for related pairs in the mid-ventral region of left inferior frontal gyrus (IFG, BA 45). Effects of association strength in the visual–auditory semantic judgment task: (c) stronger association produced greater activation for related pairs in the anterior region of left inferior parietal lobule (IPL, BA 40); (d) weaker association produced greater activation for related pairs in the mid-ventral region of left inferior frontal gyrus (IFG, BA 45).

Fig. 2

(a) Effects of age in the visual–visual semantic judgment task. Increasing age, partialled for accuracy, was correlated with greater activation in the mid-ventral region of left inferior frontal gyrus (IFG, BA 45) for related pairs compared to perceptual controls. (b) Effects of age in the visual–auditory semantic judgment task. Increasing age, partialled for accuracy, was correlated with greater activation in the mid-ventral region of left inferior frontal gyrus (IFG, BA 45) for related pairs compared to perceptual controls.

Fig. 3

Age differences in signal intensity for the visual–visual task and the visual–auditory task. Beta values were taken from the peak voxels of the mid-ventral region of left inferior frontal gyrus (BA 45) for the weaker association effect.