The spectral exponent of the resting EEG indexes the presence of consciousness during unresponsiveness induced by propofol, xenon, and ketamine
Michele A. Colombo, Martino Napolitani, Melanie Boly, Olivia Gosseries, Silvia Casarotto, Mario Rosanova, J. F. Brichant, Pierre Boveroux, Steffen Rex, Steven Laureys, Marcello Massimini, Arturo Chieregato, Simone Sarasso
Neuroimage January 11, 2019 DOI: 10.1016/j.neuroimage.2019.01.024 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Controlled experimental study Peer reviewed |
|---|---|
| Sample size | 15 |
| Population | Healthy participants |
| Interventions | Xenon Propofol Ketamine |
| Topics | Ketamine Esketamine |
| Keywords | Propofol Xenon Exponent Anesthesia Electroencephalography Consciousness Nuclear magnetic resonance Atomic physics |
| Citations | 359 |
| Key findings | A steeper decay of the resting EEG power spectral density reliably indexed unconsciousness under xenon and propofol anesthesia, while ketamine preserved a wakefulness-like decay consistent with consciousness. |
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 β, for a broad band (1-40 Hz) and narrower sub-bands (1-20 Hz, 20-40 Hz). Within-subject anesthetic changes in β were assessed. Furthermore, based on β, '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 (20-40 Hz)-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.
Comparable studies
Other experimental studies on ketamine, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Ketamine activates psychosis and alters limbic blood flow in schizophrenia Schizophrenic individuals | 1995 | Experimental study | |
| Ketamine Increases Human Motor Cortex Excitability to Transcranial Magnetic Stimulation Normal human subjects | 2003 | Experimental study | n = 7 |
| Evidence that Subanesthetic Doses of Ketamine Cause Sustained Disruptions of NMDA and AMPA-Mediated Frontoparietal Connectivity in Humans Human participants | 2015 | Experimental study | |
| Simultaneous population pharmacokinetic modelling of ketamine and three major metabolites in patients with treatment‐resistant bipolar depression Patients with treatment-resistant bipolar depression | 2012 | Population pharmacokinetic analysis | n = 9 |
| Ketamine administration reduces amygdalo‐hippocampal reactivity to emotional stimulation Healthy subjects | 2016 | Experimental study with fMRI and resting-state fMRI | n = 23 |
Citations in the library
Cited by 60
- Consciousness among delta waves: a paradox? Brain March 6, 2021
- Consciousness and complexity: a consilience of evidence Neuroscience of Consciousness 2021
- Consciousness is supported by near-critical slow cortical electrodynamics. Proceedings of the National Academy of Sciences February 1, 2022
- Quantifying arousal and awareness in altered states of consciousness using interpretable deep learning Nature Communications February 25, 2022
- General Anesthesia: A Probe to Explore Consciousness Frontiers in Systems Neuroscience August 14, 2019
and 55 more in the library
Cites 21
- Neural correlates of consciousness: progress and problems Nature Reviews Neuroscience April 20, 2016
- A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior Science Translational Medicine August 14, 2013
- The entropic brain: a theory of conscious states informed by neuroimaging research with psychedelic drugs Frontiers in Human Neuroscience 2014
- Stratification of unresponsive patients by an independently validated index of brain complexity Annals of Neurology September 22, 2016
- Unresponsiveness ≠ Unconsciousness Anesthesiology February 7, 2012
and 16 more in the library