Simultaneous bicoherence analysis of occipital and frontal electroencephalograms in awake and anesthetized subjects.

OBJECTIVE

Occipital electroencephalogram (EEG) activity is known to be different from the frontal EEG during wakefulness and anesthesia. However, less is known about occipital non-linear dynamics analyzed by EEG-bicoherence, which can reflect the oscillatory features that are dependent on thalamocortical modulation.

METHODS

Forty patients were anesthetized using sevoflurane (1% or 3%) combined with remifentanil. Frontal and occipital EEGs were simultaneously collected, and bicoherence was analyzed before and after induction of anesthesia.

RESULTS

Occipital awake EEGs often demonstrate a bicoherence α peak, differing from frontal awake EEGs in the absence of bicoherence growth. With 1% sevoflurane, occipital α bicoherence disappeared and frontal α bicoherence peaks appeared. Although 3% sevoflurane caused an increase in occipital δ-θ normalized power, similar to the frontal region (peak relative δ-θ power, 13.1 ± 2.2% vs. 12.2 ± 2.7%, p>0.05), occipital bicoherence showed no growth in any frequency area, contrasting with the frontal bicoherence spectrum with a conspicuous peak in the δ-θ area (19.8 ± 8.9 vs. 43.6 ± 13.8, p<0.05).

CONCLUSIONS

The occipital bicoherence spectrum in the peri-anesthesia period is quite different from the frontal bicoherence spectrum, which is not usually obvious in the power spectrum.

SIGNIFICANCE: Nonlinear regulation of the occipital EEG is different from the frontal EEG during every stage of anesthesia.