Abstract
Dyslexia is a neurodevelopmental disorder estimated to affect between 4 and 7% of the population. It is often referred to as a learning disability and is characterized by deficits in the linguistic system. To better understand the neural underpinnings of dyslexia, we examined the electroencephalography (EEG) power spectra between pre-adolescents with dyslexia and neurotypical control children during eyes closed state. We reported the differences in spontaneous oscillatory activity of each major EEG band (delta, theta, alpha, and beta) adopting a global as well as in a region-by-region and hemispheric approach to elucidate whether there are changes in asymmetry in children with dyslexia compared to controls. We also examined the relationship between EEG power spectra and clinical variables. The findings of our study confirm the presence of an atypical linguistic network, evident in children with dyslexia. This abnormal network hallmarked by a dominance of theta activity suggests that these abnormalities are present prior to these children learning to read, thus implicating delayed maturation and abnormal hypoarousal mechanisms.
Highlights
Dyslexia is a neurodevelopmental disorder of unknown etiology estimated to affect between 4 and 7% of the population [1]
We report the differences in spontaneous oscillatory activity of each major EEG band adopting a global as well as in a region-by-region and hemispheric approach to elucidate whether there are baseline changes in asymmetry in children with dyslexia compared to controls
There were no significant differences in mean age (t = 0.62; p < 0.8) between children with dyslexia and controls
Summary
Dyslexia is a neurodevelopmental disorder of unknown etiology estimated to affect between 4 and 7% of the population [1]. The disorder is often referred to as a learning disability and is characterized by core cognitive deficits in the linguistic system, specific to phonological processing [2]. Studies in dyslexia have highlighted abnormalities related to hemispheric lateralization, postulating that children with dyslexia fail to exhibit the expected left-hemispheric specialization that allows visual representations and phonological integration of printed information Orton [11, 12]. Hemispheric lateralization effects in dyslexia have been examined in structural post-mortem studies [13, 14] as well as functional imaging studies [15,16,17] during cognitive processing conditions and have been identified in areas implicating encoding, speech perception, and transferring of information between the two hemispheres. Early studies have yielded distinct activation patterns between impaired and non-impaired readers, reporting hypoactivation of brain regions of the (i) left-hemispheric regions, including inferior frontal, superior temporal, parieto-temporal, and middle-temporal, middle-occipital gyri and (ii) right-hemispheric regions that include the
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