Brain differences in dyslexia appear before children learn to read
Children who go on to develop dyslexia already show weaker brain responses to repeated written words in kindergarten, before formal reading lessons start. Their responses to faces, houses, and objects look much like those of their peers.
The study published in Developmental Cognitive Neuroscience reveals that children, who would later develop dyslexia, display subtle differences in how a visual-language brain region responds to repeated written words in kindergarten. This occurs before any formal reading lessons commence. Notably, these children process repeated faces, houses, and objects similarly to their peers, indicating that these early brain differences in dyslexia are specifically linked to print and not a general struggle in adapting to repeated visual stimuli.
Dyslexia is a condition characterized by persistent difficulty reading accurately and fluently despite average intelligence and appropriate instruction. A proposed explanation for dyslexia involves neural adaptation, where brain cells respond less intensely to repeated items compared to encountering new ones, reflecting the brain's efficiency in recognizing familiar patterns and categorizing specific types of information.
Initial findings from a 2016 neuroimaging study on adults and school-age children supported this theory, observing weaker neural adaptation in individuals with dyslexia when exposed to repeated spoken words, written words, faces, and objects. These findings suggested that a broad inability to swiftly adapt to repeated input could be a fundamental cause of dyslexia, rather than a consequence.
However, subsequent studies in adults and older children produced mixed results. A common limitation of earlier studies was that all participants already had reading skills, which prevented researchers from determining whether weaker brain adaptation precedes reading difficulties or results from less practice. A crucial area of reading occurs in the left ventral occipito-temporal cortex, a brain region located at the bottom of the left hemisphere, where visual and language areas intersect.
A 2018 multimodal brain-imaging study suggested that this region's back section processes visual shapes, while its front section connects written words to the language network. This foundational brain development begins early, as a 2023 longitudinal study of five-year-old pre-readers revealed that brain connections at age five predicted where word specialization would emerge at age eight.
Young children also acquire letters informally at home, providing the brain with an initial opportunity to adapt to print. A 2023 study by Anna Banaszkiewicz, Katarzyna Jednoróg, and colleagues from the Nencki Institute of Experimental Biology of the Polish Academy of Sciences utilized the same Polish cohort to examine whether weaker adaptation in dyslexia predates reading instruction.
The researchers scanned six-year-old kindergarteners' brains prior to formal schooling and again in third grade (two pandemic-related intermediate visits were excluded due to low attendance). Targeted region-of-interest group comparisons were performed as non-preregistered exploratory analyses, while whole-brain tests and longitudinal analyses across all 47 children with usable scans at both ages were also conducted.
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