Examining the Relationship Between Home Literacy Environment and Neural Correlates of Phonological Processing in Beginning Readers With and Without a Familial Risk for Dyslexia: An fMRI Study

Abstract

Purpose: Developmental dyslexia is a language-based learning disability characterized by persistent difficulty in learning to read. While an understanding of genetic contributions is emerging, the ways the environment affects brain functioning in children with developmental dyslexia are poorly understood. A relationship between the home literacy environment (HLE) and neural correlates of reading has been identified in typically developing children, yet it remains unclear whether similar effects are observable in children with a genetic predisposition for dyslexia. Understanding environmental contributions is important given that we do not understand why some genetically at-risk children do not develop dyslexia. We predicted differences in correlation of HLE and brain activation between typically developing children and those with familial risk for developmental dyslexia, as the relationship between HLE and brain activation may interact with genetic predisposition. Methods: We investigated the relationship between HLE and the neural correlates of phonological processing in beginning readers with (FHD+, n=29) and without (FHD-, n=21) a family history of developmental dyslexia. We controlled for socio-economic status to isolate the neurobiological mechanism by which HLE affects reading development. Subjects underwent a battery of behavioral testing evaluating prereading/language skills. A composite score for HLE was obtained for each subject from responses to a parent questionnaire assessing access and exposure to literacy materials in the home. Functional MRI data were collected while children completed phonological processing tasks. Multiple regression analysis was then employed to examine the correlation between HLE score and fMRI activation during a phonological processing task for all subjects and FHD – and FHD+ groups independently. Results: The results revealed positive correlations between HLE and brain activation during a phonological processing task in the left inferior frontal gyrus, bilateral fusiform gyri, and right superior temporal gyrus for all subjects combined. In addition, group differences revealed stronger correlation of HLE with brain activation in the left inferior/middle frontal and right fusiform gyri in FHD- compared to FHD+ children, suggesting greater impact of HLE on manipulation of phonological codes and recruitment of orthographic representations in typically developing children. In contrast activation in the right precentral gyrus showed a significantly stronger correlation with HLE in FHD+ compared to FHD- children, suggesting emerging compensatory networks in genetically at-risk children. Conclusions: Our results indicate that genetic predisposition for dyslexia alters contributions of the home literacy environment to early reading skills before formal reading instruction, which has important implications for educational practice and intervention models.