• Cameron P Casey, Sean Tanabe, Zahra Z Farahbakhsh, Margaret Parker, Amber Bo, Marissa White, Tyler Ballweg, Andrew Mcintosh, William Filbey, Matthew I Banks, Yuri B Saalmann, Robert A Pearce, and Robert D Sanders.
• Department of Anesthesiology, University of Wisconsin-Madison, Madison, WI, USA. Electronic address: cpcasey3@wisc.edu.
• Br J Anaesth. 2024 Feb 1; 132 (2): 300311300-311.

BackgroundUnderstanding the neural correlates of consciousness has important ramifications for the theoretical understanding of consciousness and for clinical anaesthesia. A major limitation of prior studies is the use of responsiveness as an index of consciousness. We identified a collection of measures derived from unresponsive subjects and more specifically their association with consciousness (any subjective experience) or connectedness (specific experience of environmental stimuli).MethodsUsing published data generated through the UNderstanding Consciousness Connectedness and Intra-Operative Unresponsiveness Study (NCT03284307), we evaluated 10 previously published resting-state EEG-based measures that were derived using unresponsiveness as a proxy for unconsciousness. Measures were tested across dexmedetomidine and propofol sedation and natural sleep. These markers represent the complexity, connectivity, cross-frequency coupling, graph theory, and power spectrum measures.ResultsAlthough many of the proposed markers were associated with consciousness per se (reported subjective experience), none were specific to consciousness alone; rather, each was also associated with connectedness (i.e. awareness of the environment). In addition, multiple markers showed no association with consciousness and were associated only with connectedness. Of the markers tested, loss of normalised-symbolic transfer entropy (front to back) was associated with connectedness across all three experimental conditions, whereas the transition from disconnected consciousness to unconsciousness was associated with significant decreases in permutation entropy and spectral exponent (P<0.05 for all conditions).ConclusionsNone of the proposed EEG-based neural correlates of unresponsiveness corresponded solely to consciousness, highlighting the need for a more conservative use of the term (un)consciousness when assessing unresponsive participants.Clinical Trial RegistrationNCT03284307.Copyright © 2023 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.

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