A semantic strength and neural correlates in developmental dyslexia

Abstract

Introduction: Most studies of dyslexia focus on domains of impairment (e.g., reading and phonology, among others), but few examine possible strengths. In the present study, we investigated semantic fluency as a cognitive strength in English-speaking children with dyslexia aged 8-13.

Methods: Ninety-seven children with dyslexia completed tests of letter and semantic verbal fluency, standardized measures of reading and cognitive functions, and task-free resting-state functional magnetic resonance imaging (rs-fMRI). First, we adjusted performance on semantic fluency by letter fluency and created a residual score that was used to separate participants into high (residual >0) or average (residual <0) semantic performance groups. We then employed a psycholinguistic clustering and switching approach to the semantic fluency task and performed dynamic task-free rs-fMRI connectivity analysis to reveal group differences in brain dynamics.

Results: High and average semantic fluency groups were well-matched on demographics and letter fluency but differed on their psycholinguistic patterns on the semantic fluency task. The high semantic fluency group, compared to the average semantic fluency group, produced a higher number of words within each cluster, a higher max cluster size, and a higher number of switches. Differential dynamic rs-fMRI connectivity (shorter average dwell time and greater brain state switches) was observed between the high and average groups in a large-scale bilateral frontal-temporal-occipital network.

Discussion: These data demonstrate that a subgroup of children with dyslexia perform above average on semantic fluency tasks and their performance is strongly linked to distinct psycholinguistic patterns and differences in a task-free resting-state brain network, which includes regions previously implicated in semantic processing. This work highlights that inter-individual differences should be taken into account in dyslexia and reveals a cognitive area of strength for some children with dyslexia that could be leveraged for reading interventions.

Keywords: brain dynamics; clustering and switching approach; cognitive strength; developmental dyslexia; semantic fluency.

Figure 1

Task performance (normative percentile scores) for the children with dyslexia. Performance on semantic fluency was significantly higher compared to performance on matrix reasoning, letter fluency, and design fluency tests, p < 0.001 (***). Center lines show the medians, gray diamonds show the means, and box limits indicate the 25th and 75th percentiles of the sample.

Figure 2

Semantic fluency variables for the high and average semantic fluency groups. Sum Cluster Size (A), Max Cluster Size (B), and Number of Switches (C) all showed a significant group difference; *** < 0.001, ** < 0.01. Center lines show the medians, white diamonds show the mean, and box limits indicate the 25th and 75th percentiles of the data.

Figure 3

Brain regions emerging from a dynamic task-free resting-state functional connectivity analysis in two semantic fluency groups. The red color bar reflects significant regions where the high semantic group is greater in the variations of spatial features compared to the average semantic group. Significant group differences in spatial features (average of brain states over time) were observed in the left inferior and middle frontal gyri (IFG/MFG), inferior temporal gyri (ITG), and dorsal medial parietal lobe as well as right IFG, ITG, inferior parietal, temporoparietal junction. The clusters extended subcortically to include bilateral basal ganglia and amygdala, and right hippocampus, and thalamus. The anatomical locations of significant clusters were confirmed using the Brainnetome atlas (https://atlas.brainnetome.org/bnatlas.html). The images were peak-level and cluster-level corrected (p_FWE < 0.05) for ROIs covering the whole brain. The spectrum of colors is due to the contouring smoothing that occurs during the plotting.