Early differences in neural adaptation to written words before reading instruction in dyslexia

Reduced neural adaptation has been proposed as a neurophysiological characteristic of dyslexia, but it remains unclear whether such differences precede reading acquisition or emerge as a consequence of limited reading experience. Prior studies have focused on literate individuals, limiting developmental inferences. In this preregistered longitudinal fMRI study, children oversampled for dyslexia risk were scanned in kindergarten (prior to formal reading instruction) and again in third grade. Using the rapid adaptation paradigm, we examined neural adaptation to written words, false fonts, faces, houses and objects. Analyses focused on whole-brain effects and predefined regions of interest (ROI), including ventral occipito-temporal cortex (vOT). Dyslexic and control groups were case-control matched on age and reading skill at kindergarten. In ROI analyses, children who later developed dyslexia compared to controls showed reduced neural adaptation to written words in the left vOT already in kindergarten, despite matched pre-reading skills. This result was confirmed in individually-defined ROI analyses and was restricted to the anterior part of the vOT. The group difference remained stable across development. Across the full kindergarten sample (N = 59), adaptation to words in left vOT was modestly associated with prereading skills, including phonological awareness. No robust group differences were observed at the whole-brain level or for non-linguistic visual categories. These findings indicate small, region-specific differences in neural adaptation to print that are detectable prior to formal reading instruction. The absence of whole-brain effects and for non-linguistic visual categories suggests that neural adaptation differences in dyslexia are localized and domain-specific.