NeuroImage
January 11, 2019
Michele Colombo, Martino Napolitani, Melanie Boly et al.
359 citations
During anesthesia, people may still be conscious even though they do not respond. A marker of consciousness based on the decay rate of the power spectral density (PSD) of resting EEG—measured by the spectral exponent β—was tested in healthy participants under xenon, propofol, or ketamine anesthesia (n=5 per group). Delayed reports indicated whether consciousness was present or absent. Xenon and propofol, which abolish consciousness, caused a steeper PSD decay (more negative β) compared to wakefulness. Ketamine, which preserves consciousness, showed a PSD decay similar to wakefulness overall but a flattening in high frequencies (20–40 Hz). The spectral exponent correlated strongly with the Perturbational Complexity Index (PCI), supporting its use as a marker of consciousness.
February 26, 2013
Vincent Bonhomme, P Boveroux, J. F. Brichant et al.
71 citations
Hypnotic anesthetic agents alter consciousness by targeting specific brain networks in a dose-dependent manner. Higher-order networks involved in mental content and sub-cortical networks regulating thalamic activity are affected first as concentrations increase and inhibitory neurotransmission is enhanced. Lower-order sensory networks, including thalamo-cortical connectivity within them, are preserved even at concentrations that suppress responsiveness, though cross-modal sensory interactions are inhibited. Thalamo-cortical connectivity into consciousness networks decreases with higher concentrations and becomes anti-correlated between thalamus and cortex at the deepest sedation levels when the subject is non-responsive. Whether these changes occur with agents that inhibit excitatory neurotransmission remains unknown, and the link between fMRI observations and biochemical targets is still unidentified.
Scientific Reports
November 5, 2018
Matthieu Darracq, Chadd M. Funk, Daniel Polyakov et al.
49 citations
Sleep and anesthesia alter conscious experience, which can be absent (unconsciousness) or take the form of dreaming where sensory stimuli are not incorporated (disconnected consciousness). Using transcranial magnetic stimulation-electroencephalography over parietal regions, evoked alpha power (8-12 Hz) decreased during disconnected consciousness in rapid eye movement sleep and ketamine anesthesia compared to wakefulness. In unconscious states of propofol anesthesia and non-rapid eye movement sleep, evoked low-gamma power (30-40 Hz) decreased compared to wakefulness or disconnected consciousness. These findings, confirmed with dream reports from serial awakenings, suggest suppression of evoked alpha activity may mark sensory disconnection.