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Anaesthesia and the Brain: when do individuals stop perceiving the outside world?

Despite the 100,000s of anaesthetics administered daily worldwide, we still have no robust way of knowing when a patient stops perceiving the outside world under general anaesthesia. We used multimodal EEG-FMRI to dissect the processes by which individuals lose and regain consciousness under anaesthesia. We found that, after loss of behavioural responsiveness, each individual's EEG slow-wave activity (SWA, 0.5-1.5Hz) rose to saturation and remained constant despite increasing anaesthetic concentrations. Simultaneously collected FMRI data showed that at SWA saturation, the thalamocortical system became isolated from sensory stimuli and a more fundamental cortical network persisted. Furthermore, the peak EEG-SWA level correlated with the individual’s prefrontal grey matter volume indicating maximal involvement of potentially recruitable cortical neurons. By applying Bayesian algorithms to clinical EEG data, I will present data on the existence of SWAS during surgical anaesthesia and discuss its potential for depth of anaesthesia monitoring.