The spectral exponent of the resting EEG indexes the presence of consciousness during unresponsiveness induced by propofol, xenon, and ketamine

By M. Colombo, M. Napolitani, Melanie Boly, Olivia Gosseries, Silvia Casarotto, Mario Rosanova, Jean-François Brichant, Pierre Boveroux, S. Rex, Steven Laureys and 3 more. NeuroImage, 2019

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ABSTRACT Despite the absence of responsiveness during anesthesia, conscious experience may persist. However, reliable, easily acquirable and interpretable neurophysiological markers of the presence of consciousness in unresponsive states are still missing. A promising marker is based on the decay‐rate of the power spectral density (PSD) of the resting EEG. We acquired resting electroencephalogram (EEG) in three groups of healthy participants (n=5 each), before and during anesthesia induced by either xenon, propofol or ketamine. Dosage of each anesthetic agent was tailored to yield unresponsiveness (Ramsay score=6). Delayed subjective reports assessed whether conscious experience was present (‘Conscious report’) or absent/inaccessible to recall (‘No Report’). We estimated the decay of the PSD of the resting EEG—after removing oscillatory peaks—via the spectral exponent &bgr;, for a broad band (1–40Hz) and narrower sub‐bands (1–20Hz, 20–40Hz). Within‐subject anesthetic changes in &bgr; were assessed. Furthermore, based on &bgr;, ‘Conscious report’ states were discriminated against ‘no report’ states. Finally, we evaluated the correlation of the resting spectral exponent with a recently proposed index of consciousness, the Perturbational Complexity Index (PCI), derived from a previous TMS‐EEG study. The spectral exponent of the resting EEG discriminated states in which consciousness was present (wakefulness, ketamine) from states where consciousness was reduced or abolished (xenon, propofol). Loss of consciousness substantially decreased the (negative) broad‐band spectral exponent in each subject undergoing xenon or propofol anesthesia—indexing an overall steeper PSD decay. Conversely, ketamine displayed an overall PSD decay similar to that of wakefulness—consistent with the preservation of consciousness—yet it showed a flattening of the decay in the high‐frequencies (20–40Hz)—consistent with its specific mechanism of action. The spectral exponent was highly correlated to PCI, corroborating its interpretation as a marker of the presence of consciousness. A steeper PSD of the resting EEG reliably indexed unconsciousness in anesthesia, beyond sheer unresponsiveness. HIGHLIGHTSUnconsciousness does not imply unresponsiveness.Consciousness is abolished during xenon and propofol, yet preserved during ketamine.EEG Spectral exponent indexes the 1/f‐like decay of non‐oscillatory PSD background.Xenon and propofol steepen broad‐band decay; ketamine flattens high‐frequency decay.Spectral exponent separates un/consciousness in anesthesia‐induced unresponsiveness.

Subfields: Anesthesiology and Pain Medicine, Cellular and Molecular Neuroscience, Cognitive Neuroscience

View Paper: https://www.semanticscholar.org/paper/960e89a91dd065008e33373617c5860f747ffde8

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Citations in the corpus

Aperiodic Dynamics of Cell Assemblies Recruited for L1 and L2 Processing of French Wh-Dependencies Highlight a Temporo-Parietal Engagement in Syntax (2026, unknown): “Crucially, aperiodic activity also shifts in task processing [67] and has been tied to arousal [68], consciousness [69,70], and performance [71–73], reflecting close ties between aperiodic activity and functional connectivity [74].”
Relating ADHD to the aperiodic component of the EEG signal in both males and females across development (2026, unknown): “…experiment involving macaques, the aperiodic exponent reliably tracked both the induction and recovery from propofol-anesthesia, suggesting that a steeper aperiodic exponent may reflect, in part, greater GABAergic inhibition in the brain, a finding later replicated in humans (Colombo et al., 2019).”
Hemispherotomy leads to persistent sleep-like slow waves in the isolated cortex of awake humans (2025, unknown): “…exponent has been validated as a reliable EEG marker of the level of consciousness across a range of physiological [52–60], pharmacological [55, 61–65], and pathological states [62,64,66,67], including conditions of disconnected consciousness such as ketamine-induced dreaming and locked-in…”
Reevaluating the neural noise in dyslexia using biomarkers from electroencephalography and high-resolution magnetic resonance spectroscopy (2025, unknown): “However, there are also pharmacological studies providing mixed results ( Colombo et al., 2019 ; Salvatore et al., 2024 ).”
The development of aperiodic and periodic resting-state power between early childhood and adulthood: New insights from optically pumped magnetometers (2024, result): “The link between E/I balance and the spectral slope has been supported by studies examining changes in the aperiodic slope under pharmacological interventions known to modify inhibitory and excitatory neural activity (Colombo et al., 2019; Gao et al., 2017; Fig.”
Aperiodic EEG and 7T MRSI evidence for maturation of E/I balance supporting the development of working memory through adolescence (2024, background): “…E relative to I or increasing I relative to E) via propofol (Colombo et al., 2019), diazepam (Gonza-lez-Burgos et al., 2023; Salvatore et al., 2024), MK-801 (Gonza-lez-Burgos et al., 2023), ketamine (Colombo et al., 2019), or xenon (Colombo et al., 2019), all steepen the aperiodic slope.”
Periodic and Aperiodic EEG Features as Potential Markers of Developmental Dyslexia (2023, background): “At the intra-individual level, anesthetics-induced changes in subjects’ consciousness levels influence the decaying pattern of the aperiodic power across frequencies [33,43].”
The development of oscillatory and aperiodic resting state activity is linked to a sensitive period in humans (2023, background): “The Lf-Slope of the aperiodic component was significantly steeper (more negative slope), and the Hf-Slope of the aperiodic component was significantly flatter (less negative slope) in CB and CC participants compared to the typically sighted controls.”
Periodic and aperiodic neural activity displays age-dependent changes across early-to-middle childhood (2021, background): “Studies have shown aperiodic activity to be modulated by task-performance (He et al., 2010), level of arousal (Lendner et al., 2020), and drug-induced states (Colombo et al., 2019; Muthukumaraswamy & Liley, 2018; Waschke et al., 2021).”
Separating Neural Oscillations from Aperiodic 1/f Activity: Challenges and Recommendations (2021, background): “Indeed, (Colombo et al., 2019) could link this index to the 1/f exponent during wakefulness and anesthesia yielding similar results with both methods.”
Linking the multiple-demand cognitive control system to human electrophysiological activity (2025, unknown): “…et al., 2018; Donoghue et al., 2020; Ka ł a-ma ł a et al., 2024; Voytek et al., 2015), sleep stages (Lendner et al., 2020), levels of consciousness (Colombo et al., 2019), psychiatric diseases such as ADHD (Robertson et al., 2019) and schizophrenia (Molina et al., 2020), and various aspects of…”