Tracking the coupling of two electroencephalogram series in the isoflurane and remifentanil anesthesia

•Through nonlinear model and surrogate analysis, the permutation cross-mutual information is a better method to estimate coupling of nonlinear systems.•The permutation cross-mutual information can describe the coupling changes of EEG series under isoflurane and remifentanil anesthesia.•Proposed permutation cross-mutual information has been proved to be a suitable measure to discriminate between the consciousness state and the anesthesia-induced unconsciousness state.

ObjectiveCoupling in multiple electroencephalogram (EEG) signals provides a perspective tool to understand the mechanism of brain communication. In this study, we propose a method based on permutation cross-mutual information (PCMI) to investigate whether or not the coupling between EEG series can be used to quantify the effect of specific anesthetic drugs (isoflurane and remifentanil) on brain activities.MethodsA Rössler–Lorenz system and surrogate analysis was first employed to compare histogram-based mutual information (HMI) and PCMI for estimating the coupling of two nonlinear systems. Then, the HMI and the PCMI indices of EEG recordings from two sides of the forehead of 12 patients undergoing combined remifentanil and isoflurane anesthesia were demonstrated for tracking the effect of drug on the coupling of brain activities. Performance of all indices was assessed by the correlation coefficients (Rij) and relative coefficient of variation (CV).ResultsThe PCMI can track the coupling strength of two nonlinear systems, and it is sensitive to the phase change of the coupling systems. Compared to the HMI, the PCMI has a better correlation with the coupling strength in nonlinear systems. The PCMI could track the effect of anesthesia and distinguish the consciousness state from the unconsciousness state. Moreover, at the embedding dimension m = 4 and lag τ = 1, the PCMI had a better performance than HMI in tracking the effect of anesthesia drugs on brain activities.ConclusionsAs a measure of coupling, the PCMI was able to reflect the state of consciousness from two EEG recordings.SignificanceThe PCMI is a promising new coupling measure for estimating the effect of isoflurane and remifentanil anesthetic drugs on the brain activity.