EEG spectra in severely dyslexic men: rest and word and design recognition

To identify and localize differences in brain functioning, electrical activity was recorded with a full complement of scalp electrodes in 14 healthy, severely dyslexic men (mean age = 22 years, S.D. = 3) and 15 matched controls during rest and during word and design recognition. The electroencephalograms were spectrum analyzed, and the mean amplitude in each of 5 bands - delta, theta, alpha, slow beta and fast beta - compared topographically between conditions and groups. The two tasks did not elicit differentially lateralized patterns of electrical activity, but produced anteroposterior differences in alpha and theta. The Designs tasks, more difficult for both groups, was associated with less posterior alpha than was the Words task. The strongest group difference was likewise seen along an anteroposterior axis on the Designs task. With performance equal to that of controls, the dyslexics showed relatively greater fronto-central theta and less posterior theta (a more activated state), suggesting that dyslexics were compensating for less efficient information processing. There were no group differences in overall amplitude in any band for any condition. The differences in the topographical distribution of theta may reflect subtle differences in brain organization or compensatory recruitment of widely distributed neuronal networks.