Propofol anesthesia induces phase synchronization changes in EEG

Objective: Phase coupling between EEG channel pairs in various frequency ba nds was evaluated during propofol anesthetic induction and recovery periods . Methods: Twenty-three patients participated in the study. Phase synchroniza tion indices based on the Hilbert transform were investigated on frequency bands 0.05-1 Hz, 1-4 Hz, 4-8 Hz. 8-12 Hz and 12-16 Hz for all pairs of the 9 EEG channels covering midline and frontal areas. A straight line was used to approximate the index values as a function of time and the Sign Test st atistics were applied to the slope parameters. Results: Systematic phase synchronization changes were detected. Generally, phase synchronization in the sub-delta band decreased during the induction and increased during the recovery, while the directions were reversed in t he alpha band. The changes were dependent on the channel pair. In the delta , theta and beta bands, the changes were aligned more irregularly than in t he sub-delta or in the alpha bands. Highly asymmetric behavior between the induction and the recovery periods was also observed in these bands. Conclusions: Induction and recovery from propofol anesthesia changes the ph ase synchronization between the EEG channels. The passband and location-spe cific behavior of these changes reveals the effects of the anesthetic to th e different neural mechanisms. (C) 2001 Elsevier Science Ireland Ltd. All r ights reserved.