EEG correlates of developmental dyslexia: a systematic review

Abstract

Dyslexia is one of the most studied learning disorders. Despite this, its biological basis and main causes are still not fully understood. Electroencephalography (EEG) could be a powerful tool in identifying the underlying mechanisms, but knowledge of the EEG correlates of developmental dyslexia (DD) remains elusive. We aimed to systematically review the evidence on EEG correlates of DD and establish their quality. In July 2021, we carried out an online search of the PubMed and Scopus databases to identify published articles on EEG correlates in children with dyslexia aged 6 to 12 years without comorbidities. We follow the PRISMA guidelines and assess the quality using the Appraisal Tool questionnaire. Our final analysis included 49 studies (14% high quality, 63% medium, 20% low, and 2% very low). Studies differed greatly in methodology, making a summary of their results challenging. However, some points came to light. Even at rest, children with dyslexia and children in the control group exhibited differences in several EEG measures, particularly in theta and alpha frequencies; these frequencies appear to be associated with learning performance. During reading-related tasks, the differences between dyslexic and control children seem more localized in the left temporoparietal sites. The EEG activity of children with dyslexia and children in the control group differed in many aspects, both at rest and during reading-related tasks. Our data are compatible with neuroimaging studies in the same diagnostic group and expand the literature by offering new insights into functional significance.

An Overview on Electrophysiological and Neuroimaging Findings in Dyslexia

“…Aberrant OTC activation has also been shown to be linked to rapid automatic naming and deficits in letter and word recognition in dyslexia ( 6 ). Furthermore, the hypo-activation of the left TPC during phonological processing tasks among dyslexic children and adults is a consistent finding in dyslexia ( 23 ). Activation in TPC is normally increased as a function of greater efforts in mapping printed letters to phonology.…”

“…Moreover, some studies have linked the reduction of alpha activity to phonological processing problems in dyslexia. It should be noted that alpha waves are the dominant oscillations in the human brain that play an active role in information processing ( 23 ).…”

Individual Differences in Inhibitory Control Relate to Neural Efficiency During Reading

“…In addition, several studies have shown differences in theta power between individuals with dyslexia, a reading‐related learning disability, as compared with those without dyslexia (e.g., Arns, Peters, Breteler, & Verhoeven, 2007; Galin et al, 1992; Klimesch et al, 2001; Spironelli, Penolazzi, & Angrilli, 2008; Spironelli, Penolazzi, Vio, & Angrilli, 2006). In a recent systematic review, Cainelli, Vedovelli, Carretti, and Bisiacchi (2022) found that while there was large variability across study methodology, one of the most consistent findings is that at both rest and during reading, children with dyslexia show differences in the theta frequency as compared with children in the control group. Finally, while the work is more limited, there is also evidence of a causal relation between theta‐based activity and performance on language and reading tasks.…”

Periodic and Aperiodic EEG Features as Potential Markers of Developmental Dyslexia

“…In addition to task-related electrophysiological alterations, spectral analysis revealed anomalies also in the endogenous (i.e., resting-state) neural activity of the DD population. Results from previous studies described increased delta/theta activity and decreased alpha power in children with DD at rest [ 8 , 13 ]. Furthermore, another study showed an asymmetrically distributed alpha and beta power compared to controls [ 13 ].…”

“…Many studies have described significant alterations of oscillatory EEG activity in children with DD compared to controls when performing different reading-related tasks. A recent review illustrated how these alterations generally regard theta (~4–7 Hz), alpha (~8–12 Hz), and beta (~13–30 Hz) frequency bands [ 8 ]. More specifically, children with reading impairments showed increased theta power during pseudowords encoding [ 9 ] and phonological processing [ 10 ].…”