Cortical sources of resting state EEG rhythms are abnormal in dyslexic children

Abstract: Objective: Previous studies have been inconclusive whether dominant resting state alpha rhythms differ in amplitude in dyslexic subjects when compared to control subjects, being these rhythms considered as a reflection of effective cortical neural synchronization and cognition. Here we used a validated EEG source estimation to test the hypothesis that resting state alpha rhythms are abnormal in dyslexic subjects and are related to reading deficits. Methods: Eyes-closed resting state electroencephalographic (EEG) data were recorded in 26 dyslexics (12 males, mean age of 11years±0.5standard error of mean, SEM) and 11 age-matched normal control subjects (8 males, mean age of 11years±0.7SEM). EEG rhythms of interest, based on individual alpha frequency peak, were the following: about 2–4Hz (delta), 4–6Hz (theta), 6–8Hz (alpha 1), 8–10Hz (alpha 2), and 10–12Hz (alpha 3). For the higher frequencies, we selected beta 1 (13–20Hz), beta 2 (20–30Hz), and gamma (30–40Hz). Cortical EEG sources were estimated by low resolution electromagnetic tomography (LORETA). LORETA solutions were normalized across all voxels and frequencies. Results: Compared to the control children, the dyslexics showed lower amplitude of parietal, occipital, and temporal alpha 2 and alpha 3 sources. In the dyslexics, some of these sources were correlated to reading time of pseudo-words (parietal alpha 2, r =−0.56, p =0.02; parietal alpha 3, r =−0.58, p =0.02; temporal alpha 3, r =−0.57, p =0.02); the higher the alpha power, the shorter the reading time. Conclusions: Dyslexic children are characterized by limited abnormalities of resting state EEG rhythms as to topography (posterior regions) and frequency (alpha), which were related to phonological encoding (pseudo-words reading). Significance: Dyslexia may be associated to some functional impairment of cortical neuronal synchronization mechanisms involved in the resting state condition. [Copyright &y& Elsevier]