Spatial Analytic Phase Difference of EEG activity during anesthetic-induced unconsciousness

OBJECTIVE A number of studies provide supporting evidence for changes in synchronization during anesthetic-induced unconsciousness. This study investigates how anesthetic administration affects the widespread patterns of phase synchrony. METHODS The recently introduced method of Spatial Analytic Phase Difference (SAPD) was used to measure changes in synchrony in the electroencephalogram (EEG) activity of 29 patients undergoing routine surgery. Analysis was performed over 9 frequency bands: (i) δ (1.5-3.5Hz); (ii) θ (3.5-7.5Hz); (iii) α1 (8-10Hz); (iv) α2 (10.5-12Hz); (v) β1 (12.5-18Hz); (vi) β2 (18.5-21Hz); (vii) β3 (21.5-30Hz); (viii) γ1 (30.5-40Hz); and (ix) γ2 (60-80Hz). RESULTS Anesthesia was characterized by (a) large and localized synchrony increases in mid-frequency bands (8-12Hz), (b) smaller and widespread synchrony increases in higher frequency bands (30.5-40Hz, 60-80Hz), and (c) both increase and decrease of synchrony in low frequency bands (1.5-7.5Hz). CONCLUSIONS This study supports anesthetic-induced changes in synchrony, with the inducement of persistent and reversible widespread γ synchrony being most prominent. SIGNIFICANCE Our findings have implications in the study of consciousness, support existing literature in the field and contribute towards the theoretical understanding of the mechanisms behind loss of consciousness. Future investigations could result in a synchrony-based measure for monitoring the level of hypnosis of patients during surgery.

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