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Time rescaling reproduces EEG behavior during transition from propofol anesthesia-induced unconsciousness to consciousness

Abstract : General anesthesia (GA) is a reversible manipulation of consciousness whose mechanism is mysterious at the level of neural networks leaving space for several competing hypotheses. We recorded electrocorticography (ECoG) signals in patients who underwent intracranial monitoring during awake surgery for the treatment of cerebral tumors in functional areas of the brain. Therefore, we recorded the transition from unconsciousness to consciousness directly on the brain surface. Using frequency resolved interferometry; we studied the intermediate ECoG frequencies (4–40 Hz). In the theoretical study, we used a computational Jansen and Rit neuron model to simulate recovery of consciousness (ROC). During ROC, we found that f increased by a factor equal to 1.62 ± 0.09, and δf varied by the same factor (1.61 ± 0.09) suggesting the existence of a scaling factor. We accelerated the time course of an unconscious EEG trace by an approximate factor 1.6 and we showed that the resulting EEG trace match the conscious state. Using the theoretical model, we successfully reproduced this behavior. We show that the recovery of consciousness corresponds to a transition in the frequency (f, δf) space, which is exactly reproduced by a simple time rescaling. These findings may perhaps be applied to other altered consciousness states. General anesthesia (GA) is an example of a reversible manipulation of consciousness, which is performed every day in hospitals around the world. While the mechanisms that underlie the effects of anesthetics become clearer at the cellular level 1,2 , the effects of anesthetics on brain activity at the scale of functional neural networks are still debated, which leaves space for several competing hypotheses 3. GA shares many common pathways with sleep, specifically with respect to the loss and recovery of consciousness, but it also displays specific electrophysiological features that are related to drug effects. The changes in the EEG during sleep or anesthesia are empirically well described but their function and generation are still unknown 4. The loss of consciousness induced by the widely used anaesthetic propofol is associated with an increase of power in the low-frequencies of the EEG and the emergence of strong and highly structured rhythmic activities in the EEG 5–7 corresponding to frontal alpha oscillations (8 to 13 Hz) 5. Many anesthetics share the same effects 8. Moreover, for some authors, the characteristic changes in the EEG during GA are similar to those observed in the first stages of sleep 9,10. A consistent explanation for these findings is missing and the behavior is still debated, which has led to different models 3,11–14. In this article, we recorded Electrocorticography (ECOG) after stopping the infusion of anaesthetics for brain surgery requiring functional testing in awake patients. We investigated the reorganization of dynamics in local
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Submitted on : Tuesday, May 8, 2018 - 11:54:05 AM
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Salah Boussen, Andreas Spiegler, Christian Bénar, Marcel Carrère, Fabrice Bartolomei, et al.. Time rescaling reproduces EEG behavior during transition from propofol anesthesia-induced unconsciousness to consciousness. Scientific Reports, Nature Publishing Group, 2018, 8 (1), pp.6015. ⟨10.1038/s41598-018-24405-z⟩. ⟨hal-01788058⟩

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