In the search for EEG markers of human consciousness, alpha power has long been considered a reliable marker which is fundamental for the assessment of unresponsive patients from all etiologies. However, recent evidence questioned the role of alpha power as a marker of consciousness and proposed the spectral exponent and spatial gradient as more robust and generalizable indexes. In this study, we analyzed a large-scale dataset of 260 unresponsive patients and investigated etiology-specific markers of level of consciousness, responsiveness and capacity to recover. We compare a set of candidate EEG makers: 1) absolute, relative and flattened alpha power; 2) spatial ratios; 3) the spectral exponent; and 4) signal complexity. Our results support the claim that alpha power is an etiology-specific marker, which has higher diagnostic value for anoxic patients. Meanwhile, the spectral slope showed diagnostic value for non-anoxic patients only. Changes in relative power and signal complexity were largely attributable to changes in the spectral slope. Grouping unresponsive patients from different etiologies together can confound or obscure the diagnostic value of different EEG markers of consciousness. Our study highlights the importance of analyzing different etiologies independently and emphasizes the need to develop clinical markers which better account for inter-individual and etiology-dependent differences.

Jacobo D. Sitt is scientific co-founder of NeuroMeters (scientific advisory activity but no executive or management activity).

SBM is supported by the Canada Research Chairs Program (Tier II). CM is funded through Fonds de recherche du Quebec Sante (FRQS). This research is supported in part by the FRQNT Strategic Clusters Program (2020 RS4 265502 Centre UNIQUE Union Neurosciences et Artificial Intelligence Quebec). This study was funded through an NSERC Discovery Grant (RGPIN 2023 03619) and a France Canada Research Fund New Research Collaborations Program. This research was undertaken thanks in part to funding from the Canada First Research Excellence Fund and Fonds de recherche du Quebec, awarded to the Healthy Brains, Healthy Lives initiative at McGill University. This study was partly funded by the European Union (ERA PerMed JTC2019 PerBrain, grant to JDS) and FLAG ERA project ModelDXConsciousness. DM received individual funding from Ecole Doctorale Frontieres de l'Innovation en Recherche et Education Programme Bettencourt.

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Ethics committee/IRB of the Pitie - Salpetriere hospital gave ethical approval for this work under the code Recherche en soins courants.

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The participants of this study did not give consent for their data to be shared publicly. Due to the sensitive nature of the research EEG data is not publicly available. Derived data supporting the findings of this study are available upon reasonable request to the authors.