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

Abstract

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.

The Relationship between White Matter and Reading Acquisition, Refinement and Maintenance

“…This finding was also reflected in negative MD and RD relationships of the said ventral tracts with reading scores. This early emergence of ventral tracts for reading has been supported by previous studies [50,52,53] and may reflect a compensatory strategy associated with the maturation of dorsal tracts [54]. More specifically, the dorsal tracts mature later than ventral tracts, and thus, may be insufficient for phonological processing in and of themselves [54,55].…”

White matter properties differ in 6-year old Readers and Pre-readers

“…Developmentally, individual variations in diffusion properties of dorsal and ventral white matter pathways have been found to be associated with phonological skills in pre-reading children (Saygin et al 2013; Vanderauwera et al 2015; Vandermosten et al 2015) and with reading skills in older children who had learned to read (Nagy et al 2004; Beaulieu et al 2005; Deutsch et al 2005; Niogi and McCandliss 2006; Odegard et al 2009; Rimrodt et al 2010; Yeatman et al 2011; Gullick and Booth 2014; Gullick and Booth 2015). Diffusion properties have also been observed to change in association with improvements in children's reading abilities following an intensive behavioral training for reading (Keller and Just 2009) and to predict later reading outcomes in children with dsylexia (Hoeft et al 2007).…”

“…Based on dMRI studies of reading and white matter in children, we evaluated the anterior SLF and the arcuate fasciculus, the inferior longitudinal fasciculus, the corticospinal tract, the uncinate fasciculus, and posterior subdivisions of the splenium of the corpus callosum that contain fiber pathways projecting to temporal or occipital cortices. (Nagy et al 2004; Beaulieu et al 2005; Deutsch et al 2005; Niogi and McCandliss 2006; Frye et al 2008; Qiu et al 2008; Odegard et al 2009; Yeatman et al 2011; Yeatman, Dougherty, Ben-Shachar, et al 2012; Saygin et al 2013; Vanderauwera et al 2015; Vandermosten et al 2015). In tracts where we identified group differences, we planned to conduct correlation analyses between white matter properties and specific reading-related skills in order to interrogate the possible sources of individual variability that may have contributed to the observed group differences in white matter structure.…”

“…Until now, most development studies of early readers and pre-readers have primarily identified white matter differences on the basis of whether children have specific behavioral and familial risk factors for reading disorders (Saygin et al 2013; Vandermosten et al 2015). Here, evidence for white matter differences between Readers and Pre-Readers would demonstrate that white matter differences at these ages would reflect whether children had acquired the ability to read.…”

Predicting Developmental Dyslexia: A Brief Review of Genetics, Language and the Brain

“…A recent study observed FA of the left arcuate fasciculus and bilateral inferior fronto-occiptial fasciculi correlates with phonological awareness in Dutch speaking pre-readers with (N=36) and without a familial risk of DD (N=35) [48]. Children completed behavioral testing at the start of kindergarten and an MRI scan at the end of the academic year.…”