Development of Atypical Reading at Ages 5 to 9 Years and Processing of Speech Envelope Modulations in the Brain

Abstract

Different studies have suggested that during speech processing readers with dyslexia present atypical levels of neural entrainment as well as atypical functional hemispherical asymmetries in comparison with typical readers. In this study, we evaluated these differences in children and the variation with age before and after starting with formal reading instruction. Synchronized neural auditory processing activity was quantified based on auditory steady-state responses (ASSRs) from EEG recordings. The stimulation was modulated at syllabic and phonemic fluctuation rates present in speech. We measured the brain activation patterns and the hemispherical asymmetries in children at three age points (5, 7, and 9 years old). Despite the well-known heterogeneity during developmental stages, especially in children and in dyslexia, we could extract meaningful common oscillatory patterns. The analyses included (1) the estimations of source localization, (2) hemispherical preferences using a laterality index, measures of neural entrainment, (3) signal-to-noise ratios (SNRs), and (4) connectivity using phase coherence measures. In this longitudinal study, we confirmed that the existence of atypical levels of neural entrainment and connectivity already exists at pre-reading stages. Overall, these measures reflected a lower ability of the dyslectic brain to synchronize with syllabic rate stimulation. In addition, our findings reinforced the hypothesis of a later maturation of the processing of beta rhythms in dyslexia. This investigation emphasizes the importance of longitudinal studies in dyslexia, especially in children, where neural oscillatory patterns as well as differences between typical and atypical developing children can vary in the span of a year.

Neural synchronization and intervention in pre‐readers who later on develop dyslexia

“…Consistent with the current results for the SAM stimuli, the studies of Lizarazu et al (2015) and Mandke et al (2022) demonstrated a rightward lateralization at syllable rate in typical readers, but a lack thereof in dyslexic readers. A plausible interpretation for this finding can be found in Granados Barbero et al (2022), who attributed a weaker rightward lateralization in children with dyslexia to a late maturation process that normalized by the age of nine. The children in the current study were only 7–8 years old at the latest test phase, but the data indeed seem consistent with a late maturation for lateralization, which might impact reading development.…”

“…While there is strong support for atypical hemispheric specialization at syllable rate when considering the delta range (Hämäläinen et al, 2012; Lizarazu, Scotto di Covella, et al, 2021; Molinaro et al, 2016), evidence in the theta range is far more restricted. Yet, the current study is not the first in revealing an atypical hemispheric specialization in the theta range in dyslexia (Granados Barbero et al, 2022; Lizarazu et al, 2015; Mandke et al, 2022). Consistent with the current results for the SAM stimuli, the studies of Lizarazu et al (2015) and Mandke et al (2022) demonstrated a rightward lateralization at syllable rate in typical readers, but a lack thereof in dyslexic readers.…”

“…Results at theta rate are rather inconsistent. Two studies demonstrated decreased theta synchronization in dyslexia (Granados Barbero et al, 2022; Mandke et al, 2022), while two other studies demonstrated increased theta synchronization (Granados Barbero et al, 2021; Lizarazu et al, 2015). In the study of Lizarazu et al (2015), the dyslexia group also failed to demonstrate a right‐hemispheric lateralization at the theta rate.…”

“…Results for phonemic processing in the beta and low‐gamma range are also rather inconclusive. Studies demonstrated decreased synchronization (Granados Barbero et al, 2022; Mandke et al, 2022; Menell et al, 1999) mostly located in the left hemisphere (Lehongre et al, 2011, 2013; Lizarazu, Scotto di Covella, et al, 2021; Poelmans et al, 2012), increased synchronization (De Vos et al, 2017a, 2017b; Granados Barbero et al, 2022), at times restricted to the right hemisphere (Lizarazu et al, 2015), and even typical synchronization (Hämäläinen et al, 2012; Vanvooren et al, 2014). Although not yet fully unraveled, it is hypothesized that people with dyslexia display atypical neural synchronization and differential hemispheric specialization when compared to their typically developing peers.…”

“…In the study of Lizarazu et al (2015), the dyslexia group also failed to demonstrate a right‐hemispheric lateralization at the theta rate. In the study of Granados Barbero et al (2022), children with dyslexia demonstrated a belated rightward hemispheric specialization. Using a source analysis methodology, the authors demonstrated a significantly weaker rightward lateralization in children with dyslexia compared to typical readers, Notably, the dyslexic readers caught up with typical readers by the age of 9, pointing towards a late maturation process of hemispheric specialization in dyslexia.…”