Science Translational Medicine
August 14, 2013
Adenauer G. Casali, Olivia Gosseries, Mario Rosanova et al.
1,299 citations
A new index called the perturbational complexity index (PCI) can objectively measure a person's level of consciousness without requiring them to respond or interact. PCI works by using transcranial magnetic stimulation to briefly perturb the cortex and then measuring the algorithmic complexity of the resulting brain activity patterns. The index was tested on healthy individuals during wakefulness, dreaming, nonrapid eye movement sleep, and under sedation with midazolam, xenon, and propofol, as well as on patients who had emerged from coma. PCI reliably distinguished conscious from unconscious states in single individuals across all conditions, including vegetative state, minimally conscious state, and locked-in syndrome.
Annals of Neurology
September 22, 2016
Silvia Casarotto, Angela Comanducci, Mario Rosanova et al.
504 citations
A brain-based measure called the Perturbational Complexity Index (PCI) can reliably distinguish conscious from unconscious individuals, even when they cannot speak or move. The index was first validated in 150 healthy and brain-injured people who could report their conscious state, achieving perfect accuracy in separating conscious from unconscious conditions. Applied to 81 noncommunicative patients, PCI correctly identified 94.7% of those in a minimally conscious state and revealed that 9 of 43 patients diagnosed as vegetative had PCI values overlapping with conscious individuals. These findings suggest that some behaviorally unresponsive patients may retain hidden conscious capacity.
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.
Clinical EEG and Neuroscience
January 1, 2014
Simone Sarasso, Mario Rosanova, Adenauer G. Casali et al.
164 citations
Consciousness requires both functional integration and differentiation in the brain, a property termed brain complexity. Transcranial Magnetic Stimulation combined with electroencephalography (TMS/EEG) can quantify this complexity. Studies consistently show that the complexity of the cortical response to TMS collapses during loss of consciousness in deep sleep, anesthesia, and vegetative state after severe brain injury. Complexity recovers when consciousness returns during wakefulness, dreaming, the minimally conscious state, or locked-in syndrome. This approach may help understand the pathophysiology of disorders of consciousness and requires careful methodological attention.
Trends in Cognitive Sciences
December 22, 2022
Christopher Timmermann, Prisca R. Bauer, Olivia Gosseries et al.
145 citations
A neurophenomenological framework is proposed for studying non-ordinary states of consciousness (NSCs) such as hypnosis, meditation, and psychedelics. NSCs involve shifts in what appears to the experiencer or how it appears, enabling investigation of the plastic and dynamic nature of experience across mind, brain, body, and context. The approach highlights NSCs as catalysts of transformation in clinical practice by refining understanding of relationships between subjective experience and neural dynamics. Ethical implications for standard conceptions of health and pathology are outlined, along with the crucial role of experience-based know-how in NSC research and application.
Journal of Neuroscience
February 8, 2017
Jason Samaha, Olivia Gosseries, Bradley R. Postle
131 citations
Transcranial magnetic stimulation (TMS) of occipital and posterior parietal cortex can produce visual sensations called phosphenes. Using near-threshold TMS with concurrent EEG, the authors found that prestimulus power and phase in the alpha band (8–13 Hz) predicted occipital TMS phosphenes, while higher-frequency beta-band (13–20 Hz) power (but not phase) predicted parietal TMS phosphenes. TMS-evoked responses related to phosphene perception were similar across sites, showing an early posterior negativity and later parietal positivity, plus low-frequency power increase followed by broadband alpha/beta power decrease. These correlates resemble those of conscious perception of near-threshold visual stimuli. The regionally differential prestimulus predictors suggest distinct frequencies reflect cortical excitability in occipital versus parietal cortex, challenging the assumption that alpha rhythm serves as a general index of cortical excitability.
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.
Frontiers in Systems Neuroscience
August 14, 2019
Vincent Bonhomme, Cécile Staquet, Javier Montupil et al.
109 citations
General anesthesia reversibly alters consciousness without globally shutting down the brain. Depending on the agent and dose, it can produce a complete absence of subjective experience (unconsciousness), a conscious experience without environmental perception (disconnected consciousness, like during dreaming), or oriented consciousness with environmental awareness (connected consciousness). Each state may be followed by explicit or implicit memories. Progress in brain function exploration has improved understanding of neural correlates of consciousness and their alterations during anesthesia, including changes in functional and effective brain connectivity, consciousness network topology, and spatio-temporal dynamics.
Scientific Reports
March 26, 2019
Minji Lee, Benjamin Baird, Olivia Gosseries et al.
98 citations
During non-rapid eye movement sleep, conscious experiences are linked to reduced phase-locking at low frequencies (<4 Hz) and lower transitivity and clustering coefficient in delta and theta bands compared to unconsciousness, especially over parietal-occipital regions. No significant differences in Granger-causality patterns between frontal and parietal areas were found. These findings suggest that decreased local connectivity at low frequencies in posterior brain regions may indicate consciousness during sleep.
Trends in Cognitive Sciences
January 22, 2020
Charlotte Martial, Héléna Cassol, Steven Laureys et al.
90 citations
Near-death experiences (NDEs) occur during comatose states, challenging the common view that consciousness disappears when the brain shuts down. A new framework distinguishing awareness, wakefulness, and connectedness is needed to understand the phenomenon. Classical NDEs represent internal awareness experienced in unresponsive conditions, constituting an episode of disconnected consciousness. This proposal points toward new directions for NDE research and consciousness science more broadly.
Journal of Neuroscience
March 23, 2021
Diego Candia‐rivera, Jitka Annen, Olivia Gosseries et al.
81 citations
Heartbeat-evoked responses (HERs) in resting-state EEG can distinguish between postcomatose patients who are unresponsive and those in a minimally conscious state with 87% accuracy, 96% sensitivity, and 50% specificity. HERs provide more accurate classification than random EEG segments not locked to heartbeats or heart rate variability. HER-based consciousness scores correlate with glucose metabolism in the right superior temporal sulcus and right ventral occipitotemporal cortex. HERs reflect consciousness diagnosis based on brain metabolism better than behavior-based diagnosis (77% validation accuracy). These findings suggest HERs capture a capacity for consciousness that does not necessarily translate into intentional overt behavior.
Scientific Reports
December 6, 2018
Benjamin Baird, Anna Castelnovo, Olivia Gosseries et al.
74 citations
People who have frequent lucid dreams—three or more per week—show stronger functional connections between the left anterior prefrontal cortex and several brain regions, including the angular gyrus, middle temporal gyrus, and inferior frontal gyrus, compared to people who rarely or never lucid dream. These connections involve areas that are normally less active during sleep. No differences in brain structure were found. The findings suggest that frequent lucid dreaming is linked to how certain brain networks communicate, not to structural differences.
Consciousness and Cognition
November 1, 2020
Charlotte Martial, Jessica Simon, Ninon Puttaert et al.
69 citations
Two scales for measuring near-death experiences (NDEs) were evaluated. The original NDE scale showed several weaknesses. A new 20-item Near-Death Experience Content (NDE-C) scale was developed and validated, revealing a five-factor structure covering relevant dimensions. The NDE-C scale demonstrated very good internal consistency (Cronbach α = 0.85) and concurrent validity (correlations above 0.76). This new reliable scale should facilitate future research on NDEs.
PLoS ONE
May 13, 2015
Melanie Boly, Shuntaro Sasai, Olivia Gosseries et al.
69 citations
A meaningful sequence of stimuli, like movie frames, triggers varied experiences, while meaningless stimuli, like TV noise, produce a uniform experience despite physical differences. The differentiation of cortical responses, measured by Lempel-Ziv complexity of functional MRI images, reflects the overall meaningfulness of a stimulus set rather than differences among stimuli. Brain activity patterns showed highest differentiation during a movie, intermediate for a temporally scrambled movie, and minimal for spatially scrambled TV noise, even though overall cortical activation was strong and widespread in all conditions. Meaningfulness also correlated with higher information integration among cortical regions. This approach can assess stimulus meaningfulness without identifying relevant features or neural locations.
Communications Biology
June 29, 2022
Anira Escrichs, Yonatan Sanz Perl, Carme Uribe et al.
67 citations
Different brain states—resting, meditating, deep sleep, and disorders of consciousness after coma—are underpinned by distinct spatiotemporal dynamics that can be characterized using turbulence theory. Non-conscious states tend to be more synchronous, while conscious states are more asynchronous, but the work goes beyond this simple dichotomy. A model-free analysis of human neuroimaging data applied Kuramoto's turbulence framework with coupled oscillators and measured information cascades across spatial scales. A complementary model-based approach used exhaustive computer simulations of whole-brain models fitted to those measures to study information encoding. The framework shows that turbulence theory provides excellent tools for describing and differentiating between brain states.
Scientific Reports
August 5, 2016
Jaakko O. Nieminen, Olivia Gosseries, Marcello Massimini et al.
60 citations
During non-rapid eye movement (NREM) sleep, the brain's response to transcranial magnetic stimulation (TMS) differs depending on whether the person is conscious (dreaming) or not. When subjects reported no conscious experience upon awakening, TMS evoked a larger negative deflection and a shorter phase-locked response compared to when they reported a dream. The amplitude of the negative deflection—a hallmark of neuronal bistability—was inversely correlated with the length of the dream report. These findings suggest that variations in the level of consciousness within the same physiological state are associated with changes in underlying cortical bistability.
Communications biology
August 5, 2024
Charlotte Maschke, Jordan O'Byrne, Michele Angelo Colombo et al.
50 citations
Consciousness may depend on brain activity poised at criticality—a state with complex patterns and high sensitivity to disruption. Analyzing resting-state EEG from healthy volunteers under propofol, xenon, or ketamine anesthesia, the study found that unconsciousness (from propofol or xenon) shifted brain dynamics away from avalanche criticality and the edge of chaos. Ketamine anesthesia preserved consciousness (vivid dreams) and criticality. Dynamical properties from resting EEG accurately predicted individual values of the perturbational complexity index (PCI), a TMS-based consciousness measure. The findings link perturbational complexity to criticality and suggest criticality is necessary for consciousness.
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.
Brain Injury
August 1, 2014
Martino Napolitani, Olivier Bodart, Paola Canali et al.
44 citations
Transcranial magnetic stimulation combined with high-density electroencephalography (TMS-hdEEG) offers advantages over other brain imaging techniques for assessing consciousness. A key requirement for consciousness is the brain's capacity to rapidly integrate information across specialized cortical areas. TMS-EEG stimulates any cortical area and records immediate electrical responses, successfully measuring changes in brain complexity under physiological, pharmacological, and pathological conditions. This technique reliably discriminates between conscious and unconscious patients at the single subject level, though further validation as a clinical tool is needed.
Brain sciences
July 14, 2021
Charlotte Martial, Géraldine Fontaine, Olivia Gosseries et al.
37 citations
People who have had a near-death experience often report a disturbed sense of having a distinct self. In a survey of 100 individuals who scored 27 or higher out of 80 on the Near-Death-Experience Content scale, 80 had their experience in a life-threatening situation and 20 did not. Participants completed inventories measuring ego dissolution and ego inflation during their NDE, as well as a scale of nature-relatedness. Ego-dissolution scores were higher than ego-inflation scores. Total NDE intensity positively correlated with ego dissolution and, more weakly, with ego inflation and nature-relatedness. Ego dissolution also correlated with the intensity of out-of-body experiences and a sense of unity. The findings suggest that dissolved ego-boundaries are a common feature of NDEs.
Scientific reports
October 1, 2019
Charlotte Martial, Armand Mensen, Vanessa Charland-Verville et al.
36 citations
A proof-of-concept study induced near-death experience (NDE)-like features in five volunteers who had previously had a pleasant NDE by having them recall the memory under hypnosis while their brain activity was recorded with high-density EEG. The hypnosis protocol recreated NDE-like features without adverse effects and increased absorption and dissociation compared to normal consciousness recall. Recalling the NDE phenomenology was associated with increased alpha brain activity in frontal and posterior regions. The methodology offers a controlled way to prospectively study NDE-like features and their EEG correlates.
BJA Open
September 26, 2023
Javier Montupil, Paolo Cardone, Cécile Staquet et al.
32 citations
The source of consciousness is widely thought to be within the brain, and anesthesiologists have their own operational definition based on observations during anesthesia. The full functional correlates of consciousness remain unclear, but several theories have gained varying support from experiments, including those using anesthesia to reversibly alter aspects of consciousness. Understanding these mechanisms could improve patient management by enabling monitoring devices that detect different states during anesthesia: unconsciousness, internal awareness with or without conscious perception of the environment (connected or disconnected consciousness). Unresponsiveness does not guarantee absence of connectedness or consciousness. This narrative review presents current knowledge from a system-level perspective, highlighting anesthesia's contribution to theories of consciousness and proposing future research directions.
NeuroImage
February 9, 2021
Riku Ihalainen, Olivia Gosseries, Frederik van de Steen et al.
30 citations
Using dynamic causal modelling of high-density EEG recordings from 10 people during propofol anaesthesia, the study evaluated how three resting state networks—the default mode network, the salience network, and the central executive network—contribute to consciousness. Loss of consciousness reduced inter-network connectivity in the parietal cortex, especially feed-forward frontoparietal and parietal connections at the precuneus node within the default mode network. Within the salience and central executive networks, unconsciousness generated small increases in bidirectional connectivity. The most consistent predictions of consciousness came from a key set of frontoparietal connections, supporting the importance of the posterior hot zone in explaining loss of consciousness.
Scientific Reports
September 22, 2023
Victor Oswald, Audrey Vanhaudenhuyse, Jitka Annen et al.
24 citations
Self-induced cognitive trance (SICT) is a voluntary non-ordinary state of consciousness involving narrowed awareness, hyper-focused immersion, and altered perception. This study examined autonomic nervous system changes during SICT by measuring heart rate variability and respiration rate variability in 25 proficient participants across three conditions: resting state, SICT, and a mental imagery task. During SICT, participants showed increased heart rate, decreased high-frequency heart rate variability, and specific increases in respiratory amplitude, phase ratio, and respiration rate variability compared to control conditions. These findings suggest SICT is associated with reduced parasympathetic activity, indicating a hyperarousal state of the autonomic nervous system.
NeuroImage
June 1, 2024
Pradeep Kumar G, Rajanikant Panda, Kanishka Sharma et al.
20 citations
High-order interactions between brain regions, measured as synergistic and redundant information, change differently across three non-ordinary states of consciousness. During Rajyoga meditation, synergy increased across the whole brain in delta and theta brainwave bands, while redundancy decreased in frontal, central, and posterior electrodes in delta and beta bands. During hypnosis, synergy decreased in mid-frontal, temporal, and mid-centro-parietal electrodes in the delta band, and in left frontal and right parietal electrodes in the beta2 band. During auto-induced cognitive trance, synergy decreased in delta and theta bands in left-frontal, right-frontocentral, and posterior electrodes, and at the whole brain level in the alpha band. Redundancy changes during hypnosis and auto-induced cognitive trance were not significant. Subjective reports of absorption, dissociation, and mystical experience did not correlate with the high-order measures.