A DTI tractography study in pre-readers at risk for dyslexia

Highlights • First DTI-study in pre-readers with a family risk for dyslexia (FRD+). • Bilateral ventral and dorsal pathways sustain phonological awareness. • FRD+ group displayed lower FA in left ventral pathway. • No neural specialization for phonological processing in pre-reading stage. • Anomalies related to family risk of dyslexia are present prior to reading onset.
In adults and school-aged children, phonological aspects of reading seem to be sustained by left dorsal regions, while ventral regions seem to be involved in orthographic word recognition. Yet, given that the brain reorganises during reading acquisition, it is unknown when and how these reading routes emerge and whether neural deficits in dyslexia predate reading onset. Using diffusion MRI in 36 pre-readers with a family risk for dyslexia (FRD+) and 35 well matched pre-readers without a family risk (FRD−), our results show that phonological predictors of reading are sustained bilaterally by both ventral and dorsal tracts. This suggests that a dorsal and left-hemispheric specialisation for phonological aspects of reading, as observed in adults, is presumably gradually formed throughout reading development. Second, our results indicate that FRD+ pre-readers display mainly white matter differences in left ventral tracts. This suggests that atypical white matter organisation previously found in dyslexic adults may be causal rather than resulting from a lifetime of reading difficulties, and that the location of such a deficit may vary throughout development. While this study forms an important starting point, longitudinal follow-up of these children will allow further investigation of the dynamics between emerging literacy development and white matter connections.