EEG slow-wave coherence changes in propofol-induced general anesthesia: experiment and theory.

Kaier Wang,Jamie W Sleigh,Marcus T Wilson,D A Steyn-Ross,Moira L Steyn-Ross

doi:10.3389/fnsys.2014.00215

Abstract

The electroencephalogram (EEG) patterns recorded during general anesthetic-induced coma are closely similar to those seen during slow-wave sleep, the deepest stage of natural sleep; both states show patterns dominated by large amplitude slow waves. Slow oscillations are believed to be important for memory consolidation during natural sleep. Tracking the emergence of slow-wave oscillations during transition to unconsciousness may help us to identify drug-induced alterations of the underlying brain state, and provide insight into the mechanisms of general anesthesia. Although cellular-based mechanisms have been proposed, the origin of the slow oscillation has not yet been unambiguously established. A recent theoretical study by Steyn-Ross et al. (2013) proposes that the slow oscillation is a network, rather than cellular phenomenon. Modeling anesthesia as a moderate reduction in gap-junction interneuronal coupling, they predict an unconscious state signposted by emergent low-frequency oscillations with chaotic dynamics in space and time. They suggest that anesthetic slow-waves arise from a competitive interaction between symmetry-breaking instabilities in space (Turing) and time (Hopf), modulated by gap-junction coupling strength. A significant prediction of their model is that EEG phase coherence will decrease as the cortex transits from Turing–Hopf balance (wake) to Hopf-dominated chaotic slow-waves (unconsciousness). Here, we investigate changes in phase coherence during induction of general anesthesia. After examining 128-channel EEG traces recorded from five volunteers undergoing propofol anesthesia, we report a significant drop in sub-delta band (0.05–1.5 Hz) slow-wave coherence between frontal, occipital, and frontal–occipital electrode pairs, with the most pronounced wake-vs.-unconscious coherence changes occurring at the frontal cortex.

Highlights

General anesthetic drugs act to suppress the conscious state of the cortex, leading it to a natural sleep-like mode (Lancel, 1999; Franks, 2008)
SUB-DELTA EEG COHERENCE CHANGES ACROSS FIVE SUBJECTS We first examine the across-subject wake-vs.-sleep changes in sub-delta phase coherence using the methodology described in the previous section; in Section 4.2 we analyze the coherence matrices for each individual subject
Increased coherence for left- and right-temporal electrodepairs: Electrodes at the left- and right-temporal areas detect enhanced coherence. These maps of enhanced connectivities seem to be complementary to the preceding maps showing decreased frontal–occipital connectivity: coherence trends have been reversed with the significant front–back uncoupling occurring simultaneously with a left–right coupling

Summary

Introduction

General anesthetic drugs act to suppress the conscious state of the cortex, leading it to a natural sleep-like mode (Lancel, 1999; Franks, 2008). Further evidence to support the notion of strong similarity between natural deep sleep and anesthesia can be seen in the electrical activity of the cortex: both states are signposted by the abrupt onset of large, slow oscillations (0.1–1.5 Hz) in the electroencephalogram (EEG) and local field potential (Steriade et al, 1993). These rhythmic signals, which sweep through the brain during deep sleep at the rate of about 1 cycle per second (Massimini et al, 2004), have been shown to play a role in memory encoding and consolidation (Steriade and Timofeev, 2002; Walker, 2009). Tracking the emergence of slow-wave oscillations during transition to unconsciousness may help us to identify drug-induced alterations of the underlying brain state, and provide insight into the mechanisms of general anesthesia

Methods

Results

Conclusion