Evaluation of putative signatures of consciousness using specific definitions of responsiveness, connectedness, and consciousness.
British journal of anaesthesia February 1, 2024 Cameron P Casey, Sean Tanabe, Zahra Z Farahbakhsh et al.
Many EEG-based measures previously thought to indicate unconsciousness actually track sensory connectedness—awareness of the environment—rather than consciousness itself. Analyzing data from the UNderstanding Consciousness Connectedness and Intra-Operative Unresponsiveness Study, researchers tested 10 resting-state EEG markers derived from unresponsive subjects during dexmedetomidine and propofol sedation and natural sleep. While several markers correlated with reported subjective experience (consciousness), none were specific to consciousness alone; each was also linked to connectedness. Loss of normalized-symbolic transfer entropy (front to back) was associated with connectedness across all conditions, and the shift from disconnected consciousness to unconsciousness involved significant decreases in permutation entropy and spectral exponent. The findings caution against equating unresponsiveness with unconsciousness.