Speech-Brain Frequency Entrainment of Dyslexia with and without Phonological Deficits.

Juliana Dushanova,Yordanka Lalova,Stefan Tsokov,Antoaneta Kalonkina

doi:10.3390/brainsci10120920

Abstract

Developmental dyslexia is a cognitive disorder characterized by difficulties in linguistic processing. Our purpose is to distinguish subtypes of developmental dyslexia by the level of speech–EEG frequency entrainment (δ: 1–4; β: 12.5–22.5; γ1: 25–35; and γ2: 35–80 Hz) in word/pseudoword auditory discrimination. Depending on the type of disabilities, dyslexics can divide into two subtypes—with less pronounced phonological deficits (NoPhoDys—visual dyslexia) and with more pronounced ones (PhoDys—phonological dyslexia). For correctly recognized stimuli, the δ-entrainment is significantly worse in dyslexic children compared to controls at a level of speech prosody and syllabic analysis. Controls and NoPhoDys show a stronger δ-entrainment in the left-hemispheric auditory cortex (AC), anterior temporal lobe (ATL), frontal, and motor cortices than PhoDys. Dyslexic subgroups concerning normolexics have a deficit of δ-entrainment in the left ATL, inferior frontal gyrus (IFG), and the right AC. PhoDys has higher δ-entrainment in the posterior part of adjacent STS regions than NoPhoDys. Insufficient low-frequency β changes over the IFG, the inferior parietal lobe of PhoDys compared to NoPhoDys correspond to their worse phonological short-term memory. Left-dominant 30 Hz-entrainment for normolexics to phonemic frequencies characterizes the right AC, adjacent regions to superior temporal sulcus of dyslexics. The pronounced 40 Hz-entrainment in PhoDys than the other groups suggest a hearing “reassembly” and a poor phonological working memory. Shifting up to higher-frequency γ-entrainment in the AC of NoPhoDys can lead to verbal memory deficits. Different patterns of cortical reorganization based on the left or right hemisphere lead to differential dyslexic profiles.

Highlights

Children with developmental dyslexia have difficulties in acquiring reading and writing skills despite their normal scores on intelligence tests [1,2]
Some of the children with dyslexia, who performed the discrimination task with a success rate under the mean group value 64.3% in both conditions and significantly worse in comparison to the controls (83.1% ± 0.73%, 83.1% ± 0.96%, p = 0.0001, χ2 > 112.9), were assigned to a subgroup with more pronounced phonological deficits (PhoDys; age range: 7.8–8.6, 7 boys, 4 girls)
Other dyslexics with a success rate over their mean group value (64.3%) and with lower achievements (73.1% ± 1.21%, 73.5% ± 1.74%, p = 0.0001, χ2 > 27.2) than the control group were included in a subgroup with less pronounced phonological deficits (NoPhoDys, age range: 7.6–8.3; 9 boys, 6 girls)

Summary

Introduction

Children with developmental dyslexia have difficulties in acquiring reading and writing skills despite their normal scores on intelligence tests [1,2]. According to the “dual route” model, the words can be read either by the lexical or sublexical route [3]. The words are directly recognized as lexicon members and associated with verbal semantic representations, when they are familiar, automatically identified by their visual form [3]. When the children’s deficits are in phonological skills (so-called phonological dyslexia [5]), they probably use the lexical route to compensate for the sublexical route [6], and naming irregular words well, but not pseudo-words

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