Brain Laterality in Dyslexia Seen during Literacy Development and Early Training

TL;DR

Children with dyslexia show different brain laterality patterns during literacy development compared to typical readers, and literacy training affects both brain hemispheres.

Contribution

The study reveals a unique developmental pattern of brain laterality in dyslexia during early literacy training.

Findings

The Typical group showed a shift from no ear advantage to a right ear advantage with age.

The Dyslexia group started with a right ear advantage but showed no dominance in the Literacy stage.

Early literacy training influenced both hemispheres in children with dyslexia.

Abstract

The main finding was that the developmental pattern of brain laterality from the ages of 6 to 11 in the Dyslexia group differed both from the pattern of the Typical group and from a frequently seen pattern in dyslexia.

During the period in which children learn to read and write, a gradual shift from right to left hemisphere dominance for language is typically seen. However, in children with dyslexia, a deviant pattern is described in the literature. As part of a larger longitudinal study (The Bergen Longitudinal Dyslexia Study), the present study aimed to assess this development from an early age before children learn to read and write. Dichotic listening (DL), which is a non-invasive test, was used to assess the development of brain laterality in a Typical group and a Dyslexia group. The participants received yearly sessions of evidence-based literacy training at ages 5 to 7. The Typical group showed increasing ear scores and a shift from no ear advantage in the Pre-literacy stage (age 6), indicative of no hemisphere dominance, to a right ear advantage, indicative of a left hemisphere dominance, in the Emergent literacy stage (age 8) and the Literacy stage (age 11). The Dyslexia group showed a different pattern, with a significant right ear advantage at age 6, indicative of a right hemisphere dominance, and increasing ear scores at ages 8 and 11; however, no ear dominance was observed in the Literacy stage. The results point to an effect of relevant, evidence-based training affecting both right and left hemispheres in dyslexia, which should form a basis for further research.

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