Inter-hemispheric functional coupling of eyes-closed resting EEG rhythms in adolescents with Down syndrome

Objective: We tested the hypothesis that inter-hemispheric directional functional coupling of eyes-closed resting EEG rhythms is abnormal in adolescents with Down syndrome (DS). Methods: Eyes-closed resting EEG data were recorded in 38 DS adolescents (18.7 years +/- 0.67 SE, IQ = 49 +/- 1.9 SE) and in 17 matched normal control subjects (NYoung = 19.1 years +/- 0.39 SE). The EEG data were recorded from 8 electrodes (Fp1, Fp2, C3, C4, T3, T4, O1, O2) referenced to vertex. EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), and beta 2 (20-30 Hz). Power of EEG rhythms was evaluated by FFT for control purposes, whereas interhemispheric directional EEG functional coupling was computed by directed transfer function (DTF). Results: As expected, alpha, beta, and gamma power was widely higher in NYoung than DS subjects, whereas the opposite was true for delta power. As a novelty, DTF (directionality) values globally prevailed from right to left occipital areas in NYoung subjects and in the opposite direction in DS patients. A control experiment showed that this DTF difference could not be observed in the comparison between DS adults with mild cognitive impairment and normal age-matched adults. Conclusions: These results indicate a peculiar abnormal directional inter-hemispheric interplay in visual occipital areas of DS adolescents. Significance: Direction of inter-hemispheric EEG functional coupling unveils a new abnormal brain network feature in DS adolescents. (C) 2009 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.