Metadata language
Jednoróg, Katarzyna (1981- ) : Supervisor
Publisher:Nencki Institute of Experimental Biology PAS
Place of publishing: Date issued/created: Description:[2], 140 pages : illustrations ; 30 cm ; Bibliography ; Summary in Polish
Degree name: Degree discipline : Degree grantor:Nencki Institute of Experimental Biology PAS ; degree obtained: 10.10.2025
Type of object: Subject and Keywords:Dyslexia ; EEG ; Excitation / inhibition imbalance ; Multisensory integration ; Neural noise ; Sex differences
Abstract:
Dyslexia is a specific learning disorder characterized by reduced reading fluency, accuracy, and comprehension. It affects approximately 7-12% of the population and is more commonly diagnosed in males than females. While several cognitive and neural factors associated with dyslexia have been identified, the precise causal mechanisms underlying reading difficulties remain unclear. Since reading acquisition relies on integrating auditory and visual stimuli, deficits in low-level multisensory integration may also contribute to dyslexia. Some studies have reported such deficits, but effect sizes varied depending on whether participants were matched for sex. Despite the higher prevalence of dyslexia in males and emerging evidence of sex-based differences in its neural underpinnings, no previous studies have specifically examined sex differences in multisensory integration. Thus, the first aim of this thesis was to address this gap by directly assessing sex-specific effects in low-level multisensory integration in dyslexia. One of the latest causal theories of dyslexia, the neural noise hypothesis, proposes that reading difficulties stem from increased cortical excitability, leading to cognitive impairments in phonological awareness, rapid automatized naming, and multisensory integration in dyslexia. Non-invasive estimates of excitatory/inhibitory (E/I) balance in the brain can be obtained through various electroencephalography (EEG) power spectrum measures, including aperiodic (exponent, offset) and periodic (beta and gamma power) components. To date, no study has tested the neural noise hypothesis of dyslexia by examining EEG E/I balance biomarkers in relation to proposed cognitive deficits. Thus, the second aim of this thesis was to investigate these relationships. Regarding the first aim, a study of 88 adolescents and young adults revealed that only males with dyslexia exhibited deficits in multisensory integration of simple, non-linguistic stimuli, as assessed by a simple reaction time task. At the neural level, both males and females with dyslexia showed smaller differences in responses between multisensory and unisensory conditions in the N1 and N2 components (event-related potentials related to sensory processing) compared to controls. However, in a subsample of 80 participants matched for non-verbal IQ, only males with dyslexia exhibited a smaller difference in neural responses to multisensory versus unisensory conditions in the N1 component of the left hemisphere. These findings provide novel insights into sex-specific cognitive processes related to reading difficulties. Regarding the second aim, results from a sample of 120 participants, analyzed using Bayesian statistics, revealed no evidence of group differences in any EEG E/I balance biomarkers (exponent, offset, beta power) at rest or during a spoken language task. However, a positive indirect relationship between beta power, phonological awareness, and reading speed was found. These findings do not support the prediction that cortical hyperexcitability underlies dyslexia, underscoring the need to explore alternative neural mechanisms associated with reading difficulties. Furthermore, the observed sex-specific effects in multisensory integration highlight the potential for distinct cognitive and neural pathways in males and females with dyslexia, which should be considered in future research frameworks.
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Copyright holder:Publication made available with the written permission of the author
Digitizing institution:Nencki Institute of Experimental Biology of the Polish Academy of Sciences
Original in:Library of the Nencki Institute of Experimental Biology PAS
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