Revisiting atypical language lateralization in dyslexia.
Helena Verhelst1,2, Emma M Karlsson1,2, Robin Gerrits1,3
1Department of Experimental Clinical and Health Psychology, Ghent University, Ghent 9000, Belgium.
Brain Communications
|December 8, 2025
Summary
Developmental dyslexia is linked to inconsistent brain lateralization patterns, not universally weaker ones. This inconsistency in regional brain activation may disrupt language networks, contributing to reading difficulties.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Developmental Disorders
Background:
- Hemispheric lateralization is a long-standing focus in developmental dyslexia research, but its precise role remains unclear.
- Previous studies show inconsistent findings regarding altered brain asymmetries in dyslexia, often neglecting individual variability.
- Understanding hemispheric lateralization patterns is crucial for elucidating the neurobiological underpinnings of reading and language deficits.
Purpose of the Study:
- To investigate hemispheric lateralization patterns in adults with dyslexia compared to matched controls.
- To assess the strength, direction, and consistency of brain activation across different language tasks using functional MRI.
- To explore the relationship between individual variability in lateralization and reading abilities in dyslexia.
Main Methods:
- Functional MRI (fMRI) was used to scan 35 adults with dyslexia and 35 controls.
- Participants completed three language tasks: word generation, rhyming decision, and lexical decision.
- Laterality indices were calculated to analyze global and regional brain activation patterns.
Main Results:
- No significant group differences in the absolute strength of global lateralization were found.
- Individuals with dyslexia showed greater inconsistency in regional lateralization during reading and rhyming tasks.
- Dyslexia was associated with weaker fusiform gyrus lateralization and a higher prevalence of right hemisphere activation in this area during reading.
Conclusions:
- Developmental dyslexia is characterized by inconsistent, rather than universally weaker, hemispheric lateralization patterns.
- Task-specific and regional lateralization inconsistencies may impair language network efficiency, contributing to reading deficits.
- Considering individual variability in lateralization is essential for understanding the neural basis of dyslexia and language disorders.
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