Maturation of the coherence of EEG activity in normal and learning-disabled children.

The age effect on coherence has been studied in control (98) and learning-disabled (LD, 54) school-aged children (from 6.0 to 16.8 years old). The EEG recordings were made at rest in 15 leads, and 105 pairwise combinations for coherence were calculated (each lead was compared with all the rest) for delta, theta, alpha, beta and total frequency bands. A significant increase of coherence with age was found in both groups, with a different pattern of maturation. In the control group, a significant increase with age was found in the coherences between posterior regions and vertex (Cz). A significant decrease with age in the coherence between frontal areas was observed, especially in the theta band. The LD group showed a different pattern: no significant relation with age was found in the coherence between any lead and vertex. A high effect of age on coherence between temporal regions was observed with a predominance of the left side in comparison with the contralateral and the ipsilateral. No decrease in frontal coherence was found: in the same region where the control group showed negative values with age, the LD groups had no age effect. The results obtained are discussed as differences in brain organization, in myelogenesis and synaptogenesis and an explanation of the etiology of LD is proposed.