NeuroImage
January 11, 2019
Michele Colombo, Martino Napolitani, Mélanie 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.
Neuroscience of Consciousness
January 1, 2021
Simone Sarasso, Adenauer G. Casali, Silvia Casarotto et al.
183 citations
A growing body of empirical studies has identified complexity-related measures as reliable markers of consciousness across conditions including sleep, anesthesia, hallucinatory states, coma, and related disorders. These measures were proposed independently by researchers working within different frameworks and using diverse methods. This paper systematically reviews that literature, identifies a common denominator among the measures, and traces it to theoretical principles and predictions made over 20 years ago. The authors highlight a consistent trajectory across two decades of consciousness research and offer a provisional taxonomy of the existing work. They argue that this convergence provides a solid foundation for designing future experiments and advancing the field.
Nature Communications
February 25, 2022
Minji Lee, Leandro Sanz, Alice Barra et al.
120 citations
A deep-learning-based explainable consciousness indicator (ECI) uses EEG responses to transcranial magnetic stimulation and resting-state EEG to separately quantify arousal and awareness. Tested during sleep (n=6), general anesthesia (n=16), and severe brain injury (n=34), ECI distinguishes states such as ketamine-induced anesthesia and rapid eye movement sleep, which combine low arousal with high awareness. Parietal brain regions are most relevant for these measurements. The indicator offers a way to disentangle the two components of consciousness across physiological, pharmacological, and pathological conditions.
iScience
May 19, 2023
Andres Ort, John W Smallridge, Simone Sarasso et al.
47 citations
Classical psychedelic drugs like psilocybin induce profound changes in consciousness, including heightened sensory-emotional awareness and arousal, accompanied by increased spontaneous EEG signal diversity. By combining Transcranial Magnetic Stimulation (TMS) with EEG, this work shows that psilocybin creates a state of increased chaotic brain activity, which is not due to altered complexity in causal interactions between brain regions. The study also maps regional effects of psilocybin on TMS-evoked activity, identifying changes in frontal brain structures that may relate to the phenomenology of psychedelic experiences.