Children with mathematical learning disability fail in recruiting verbal and numerical brain regions when solving simple multiplication problems

Abstract

Greater skill in solving single-digit multiplication problems requires a progressive shift from a reliance on numerical to verbal mechanisms over development. Children with mathematical learning disability (MD), however, are thought to suffer from a specific impairment in numerical mechanisms. Here we tested the hypothesis that this impairment might prevent MD children from transitioning toward verbal mechanisms when solving single-digit multiplication problems. Brain activations during multiplication problems were compared in MD and typically developing (TD) children (3rd to 7th graders) in numerical and verbal regions which were individuated by independent localizer tasks. We used small (e.g., 2 × 3) and large (e.g., 7 × 9) problems as these problems likely differ in their reliance on verbal versus numerical mechanisms. Results indicate that MD children have reduced activations in both the verbal (i.e., left inferior frontal gyrus and left middle temporal to superior temporal gyri) and the numerical (i.e., right superior parietal lobule including intra-parietal sulcus) regions suggesting that both mechanisms are impaired. Moreover, the only reliable activation observed for MD children was in the numerical region when solving small problems. This suggests that MD children could effectively engage numerical mechanisms only for the easier problems. Conversely, TD children showed a modulation of activation with problem size in the verbal regions. This suggests that TD children were effectively engaging verbal mechanisms for the easier problems. Moreover, TD children with better language skills were more effective at engaging verbal mechanisms. In conclusion, results suggest that the numerical- and language-related processes involved in solving multiplication problems are impaired in MD children.

Keywords: Arithmetic; Dyscalculia; Learning disability; Multiplication; fMRI.

Figure 1

Localizer and multiplication tasks. (A) In the Rhyming localizer (left), participants decided whether two visually presented English words rhymed or not. In the Numerosity localizer (right), participants decided which of two dot arrays had the largest number of dots. (B) In the Multiplication Task, participants were asked to evaluate whether the given answer was the correct solution to the previously seen arithmetical fact.

Figure 2

Brain regions activated in the localizer tasks. (A) The language-related network involves the left IFG and left MTG-STG. (B) The numerical processing network is situated in the right SPL.

Figure 3

Group differences in activation for multiplication in numerical ROIs. (A) On the left-hand side, image of the cluster in SPL showing greater activation for Small compared to Large problems for the MD children compared to the TD children. On the right-hand side, bar charts represent average activations for each group and for each problem size. (B) On the left-hand side, image of the cluster showing greater activation for Small compared to Large problems only in the MD children. On the right-hand side, bar charts represent average activations for each problem size.

Figure 4

Group differences in activation for multiplication in verbal ROIs. (A) On the left-hand side, images of the clusters in the STG-MTG and IFG showing greater activation for Small compared to Large problems for the TD children compared to the MD children. On the right-hand side, bar charts represent average activations from the two clusters for each group and for each problem size. (B) On the left-hand side, images of the clusters showing greater activation for Small compared to Large problems only in the TD children. On the right-hand side, bar charts represent average activations from the two clusters for each problem size.

Figure 5

Correlations of activation during multiplication with standardized measures. (A) Correlations of phonological awareness (Blending Words) with activation in the STG-MTG for small problems showing a stronger positive relationship for the TD children. (B) Correlations of phonological awareness (Blending Words) with activation in the IFG for small problems showing a stronger negative relationship for the MD children.