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.

Keywords: Connectivity; Learning; Neurophysiology; Oscillations; Reading; Spectra.

Fig. 1

Study workflow

Fig. 2

“Yes,” “no,” and “not sure” responses to the 20 items of the AXIS questionnaire for each included study

Fig. 3

Percentage of “yes,” “no,” and “not sure” responses obtained in the sample of studies for each question of the AXIS questionnaire

Fig. 4

The figure shows the results obtained in the studies using the spectral analysis of RS-EEG. In red the increases and blue the decreases obtained in children with dyslexia compared to controls; in black, if no differences were reported between the groups

Fig. 5

The stimulation task and the methodology applied to the EEG. The figure represents all conditions, so works using multiple tasks and analysis types could be overrepresented