TOPOGRAPHIC ANALYSIS OF COHERENCE AND PROPAGATION OF EEG ACTIVITY DURING SLEEP AND WAKEFULNESS

Overnight sleep EEG recorded from 21 derivations was studied in 8 heal thy subjects. The vector autoregressive model was fitted to all 21 cha nnels simultaneously. Ordinary, multiple and partial coherences and di rected transfer functions were estimated for sleep stages and wakefuln ess. Ordinary coherences give rather trivial information that coherenc e decreases with distance. Partial coherences revealed specific struct ure that was well repeatable for the subjects studied. Differences in coherence patterns between sleep stages were found by means of statist ical tests. An increase of coherence was found for sleep stages 2, 3 a nd 4. Directed transfer function made possible the identification of t he main centers from which EEG activity is spreading during sleep and wakefulness. During sleep the influence of subcortical structures was manifested by propagation of activity from the fronto-central region. The range of this interaction was highest in sleep stages 3 and 4. An EEG analysis, based on the approach of treating time series as a reali zation of one process and on the simultaneous (not pair-wise) evaluati on of signals offers new possibilities in the investigation of synchro nization and functional relations in the brain. (C) 1997 Elsevier Scie nce Ireland Ltd.