Cortical networks for vision and language in dyslexic and normal children of variable socio-economic status

Abstract

In dyslexia, anomalous activations have been described in both left temporo-parietal language cortices and in left ventral visual occipito-temporal cortex. However, the reproducibility, task-dependency, and presence of these brain anomalies in childhood rather than adulthood remain debated. We probed the large-scale organization of ventral visual and spoken language areas in dyslexic children using minimal target-detection tasks that were performed equally well by all groups. In 23 normal and 23 dyslexic 10-year-old children from two different socio-economic status (SES) backgrounds, we compared fMRI activity to visually presented houses, faces, and written strings, and to spoken sentences in the native or in a foreign language. Our results confirm a disorganization of both ventral visual and spoken language areas in dyslexic children. Visually, dyslexic children showed a normal lateral-to-medial mosaic of preferences, as well as normal responses to houses and checkerboards, but a reduced activation to words in the visual word form area (VWFA) and to faces in the right fusiform face area (FFA). Auditorily, dyslexic children exhibited reduced responses to speech in posterior temporal cortex, left insula and supplementary motor area, as well as reduced responses to maternal language in subparts of the planum temporale, left basal language area and VWFA. By correlating these two findings, we identify spoken-language predictors of VWFA activation to written words, which differ for dyslexic and normal readers. Similarities in fMRI deficits in both SES groups emphasize the existence of a core set of brain activation anomalies in dyslexia, regardless of culture, language and SES, without however resolving whether these anomalies are a cause or a consequence of impaired reading.