fMRI of syntactic processing in typically developing children: Structural correlates in the inferior frontal gyrus

Abstract

Development of syntactic processing was examined to evaluate maturational processes including left language lateralization functions and increased specialization of brain regions important for syntactic processing. We utilized multimodal methods, including indices of brain activity from fMRI during a syntactic processing task, cortical thickness measurements from structural MRI, and neuropsychological measures. To evaluate hypotheses about increasing lateralization and specialization with development, we examined relationships between cortical thickness and magnitude and spatial activation extent within the left inferior frontal gyrus (IFG) and its right hemisphere homologue. We predicted that increased activation in the left and decreased activation in the right IFG would be associated with increased syntactic proficiency. As predicted, a more mature pattern of increased thickness in the right pars triangularis was associated with decreased activation intensity and extent in the right IFG. These findings suggest a maturational shift towards decreased involvement of the right IFG for syntactic processing. Better syntactic skills were associated with increased activation in the left IFG independent from age, suggesting increased specialization of the left IFG with increased proficiency. Overall, our findings show relationships between structural and functional neurodevelopment that co-occur with improved syntactic processing in critical language regions of the IFG in typically developing children.

Constructivist developmental theory is needed in developmental neuroscience

“…During development, both mental-attentional capacity limits and learned automatisations grow with age; thus lateralisation elicited by tasks should be relative to both age and task characteristics. Further, as Nunez et al 16 found 'children with thicker cortex in the right IFG (inferior frontal gyrus) rely less on right hemisphere language areas to process linguistic/syntactic information, relying more on left hemisphere processing than children with thinner cortex in the same brain regions.' Thicker grey matter in typical children's cortex is likely to express immaturity, whereas thinner areas may indicate that the learning-contingent maturational pruning has taken place 25 -i.e., local processing has matured.…”

“…15 Similarly, thinner right inferior frontal cortices are linked to increased right inferior frontal activation in children and adolescents. 16 However, in a larger sample of adolescents no relation is observed between cortical and functional maturation-with authors cautioning against pre-assuming such an association. 17 To make matters more interesting, hemispheric involvement is not easily predictable in children; for instance, in response to cognitive tasks children and adolescents show less refined and less lateralised patterns than adults in one study 18 and similar lateralisation patterns to adults in another.…”

Left prefrontal cortex activation during sentence comprehension covaries with grammatical knowledge in children

“…The results showed a significant overlap for syntactic and semantic processing. For older children, Nuñez et al (2011) found a relation between syntactic proficiency and activation in the left IFG, superior frontal gyrus (SFG), and middle frontal gyrus (MFG) independent of age. Moreover, in Englishspeaking children at the age of 7;2 to 15;8, they observed that the amount and extent of activation within the right IFG during syntactic processing (versus rest) was negatively correlated with cortical thickness in this region, which suggests a shift from the right to the left hemisphere during this age.…”

“…However, the studies in children often failed to find significant results at the group level, indicating a high variance in language proficiency that is not related to a specific age. Rather, several studies found that activation in the left IFG correlated with individual language skills (Nuñez et al, 2011;Yeatman et al, 2010).…”

“…The experimental paradigm included transitive sentences with varying syntactic complexity, which have been successfully used before in an ERP study with 3-to 6-year-old German-speaking children (Schipke et al, in press). Due to high individual differences reported in recent developmental studies (Nuñez et al, 2011;van Ettinger-Veenstra et al, 2010;Yeatman et al, 2010), a closer look at the single-subject level should provide additional information concerning the individual developmental level. Hence, extensive behavioral testing was conducted to quantify children's performance with respect to receptive grammar skills.…”