Accelerated Recovery of Consciousness after General Anesthesia Is Associated with Increased Functional Brain Connectivity in the High-Gamma Bandwidth

Abstract

Recent data from our laboratory demonstrate that high-frequency gamma connectivity across the cortex is present during consciousness and depressed during unconsciousness. However, these data were derived from static and well-defined states of arousal rather than during transitions that would suggest functional relevance. We also recently found that subanesthetic ketamine administered during isoflurane anesthesia accelerates recovery upon discontinuation of the primary anesthetic and increases gamma power during emergence. In the current study we re-analyzed electroencephalogram (EEG) data to test the hypothesis that functional cortical connectivity between anterior and posterior cortical regions would be increased during accelerated recovery induced by ketamine when compared to saline-treated controls. Rodents were instrumented with intracranial EEG electrodes and general anesthesia was induced with isoflurane anesthesia. After 37.5 min of continuous isoflurane anesthesia, a subanesthetic dose of ketamine (25 mg/kg intraperitoneal) was administered, with evidence of a 44% reduction in emergence time. In this study, we analyzed gamma and theta coherence (measure of undirected functional connectivity) and normalized symbolic transfer entropy (measure of directed functional connectivity) between frontal and parietal cortices during various levels of consciousness, with a focus on emergence from isoflurane anesthesia. During accelerated emergence in the ketamine-treated group, there was increased frontal-parietal coherence {p = 0.005, 0.05–0.23 [95% confidence interval (CI)]} and normalized symbolic transfer entropy [frontal to parietal: p < 0.001, 0.010–0.026 (95% CI); parietal to frontal: p < 0.001, 0.009–0.025 (95% CI)] in high-frequency gamma bandwidth as compared with the saline-treated group. Surrogates of cortical information exchange in high-frequency gamma are increased in association with accelerated recovery from anesthesia. This finding adds evidence suggesting a functional significance of high-gamma information transfer in consciousness.

Glutamatergic neurons in the preoptic hypothalamus promote wakefulness, destabilize NREM sleep, suppress REM sleep, and regulate cortical dynamics

“…We filtered the frontal and occipital EEG signals into the frequency bands as described above and segmented the filtered data into non-overlapped 5-s windows. We followed the methods used in previous studies (Li et al, 2017;Pal et al, 2020) and fixed the embedding dimension ݀ ா = 3; as the time delay τ defines a broad frequency-specific window of sensitivity for NSTE (Jordan et al, 2013;Sitt et al, 2014;Ranft et al, 2016), we used τ = 64, 28, 17, 9, 6, 2, corresponding to delta (0.5 to 4 Hz), theta, sigma, beta, lowand high-gamma, respectively. For each window, we searched the transfer time δ = 1-50 (corresponding to 2 -100 ms approximately) and selected the one that generated maximum feedback (from frontal to occipital) and feedforward (from occipital to frontal) NSTE, respectively.…”

Estimation of the depth of anesthesia by using a multioutput least-square support vector regression

“…In this figure, reduced high frequency EEG bands during anesthesia with increased amplitude are shown during consciousness. The reason for this is the reduction of high frequency EEG band activity during anesthesia [3]. The frequency of EEG signal fluctuations is proportional to the level of consciousness and the level of the individual's concentration and their psychological/mental status in different frequency ranges [18].…”

“…In order to prevent the above-mentioned incidents, using intelligent methods based on the body's physiological signals is considered an appropriate alternative. Therefore, in recent years, special attention has been paid to electroencephalogram (EEG) signal processing in order to estimate the depth of anesthesia [2,3].…”

Sleep Electroencephalographic Response to Respiratory Events in Patients With Moderate Sleep Apnea–Hypopnea Syndrome

“…Let embedding dimension m = 5 and time delay l = 62, 31, 18, 16, 8, 4, corresponding to bands δ, θ, α, σ, β, and γ, respectively (Li et al, 2017). Time lag δ = 20 reflects corticocortical information flow in EEG signals (Untergehrer et al, 2014).…”