Science
September 7, 2006
Adrian M. Owen, Martin R. Coleman, Melanie Boly et al.
1,974 citations
A patient who met the clinical criteria for a vegetative state showed brain activity indistinguishable from healthy volunteers when asked to imagine playing tennis or moving around her home. Using functional magnetic resonance imaging, the patient activated the same predicted cortical areas as conscious individuals, indicating preserved conscious awareness despite appearing unresponsive. This finding suggests that some patients diagnosed as vegetative may retain covert consciousness that standard behavioral assessments cannot detect.
Nature reviews. Neuroscience
April 20, 2016
Christof Koch, Marcello Massimini, Melanie Boly et al.
1,654 citations
The neural correlates of consciousness—the minimum neural mechanisms sufficient for any one specific conscious percept—are primarily localized to a posterior cortical hot zone that includes sensory areas, rather than to a fronto-parietal network involved in task monitoring and reporting. Some candidate neurophysiological markers of consciousness have proved illusory, while measures of differentiation and integration of neural activity offer more promising quantitative indices of consciousness.
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.
Anesthesiology
September 30, 2010
Pierre Boveroux, Audrey Vanhaudenhuyse, Marie‐Aurélie Bruno et al.
645 citations
Propofol-induced unconsciousness is linked to decreased connectivity within frontoparietal networks (the default-mode and executive-control networks) and between the thalamus and these networks, with a negative correlation between thalamic and cortical activity emerging during unconsciousness. In contrast, connectivity in low-level sensory cortices (auditory and visual networks) is preserved, including their thalamocortical connections. Loss of consciousness is associated with a breakdown of cross-modal interactions between visual and auditory networks. These findings suggest that unconsciousness results from disrupted communication between sensory and higher-order frontoparietal cortices, preventing conscious perception.
Journal of Neuroscience
October 4, 2017
Melanie Boly, Marcello Massimini, Naotsugu Tsuchiya et al.
591 citations
The role of the frontal cortex in consciousness is debated. This Perspective critically reviews clinical and neuroimaging evidence for the involvement of the front versus the back of the cortex in specifying conscious contents and discusses promising research avenues.
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.
Journal of Cognitive Neuroscience
June 1, 2010
Audrey Vanhaudenhuyse, Athena Demertzi, Manuel Schabus et al.
460 citations
Resting brain activity reveals two anticorrelated cortical systems linked to conscious awareness: an extrinsic system (lateral fronto-parietal areas) associated with external awareness and an intrinsic system (medial brain areas) associated with internal awareness. In 31 healthy volunteers, external and internal awareness were significantly anticorrelated, with a mean switching frequency of 0.05 Hz, similar to BOLD fMRI slow oscillations. In 22 volunteers, fMRI showed that precuneus/posterior cingulate, anterior cingulate/mesiofrontal cortices, and parahippocampal areas (intrinsic system) correlated with internal awareness, while lateral fronto-parietal cortices (extrinsic system) correlated with external awareness.
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.
Frontiers in Psychology
January 1, 2013
Melanie Boly, Anil K. Seth, Melanie Wilke et al.
295 citations
Consciousness research over the last decade has advanced through evidence that fronto-parietal connectivity and top-down processes enable information to travel across distant cortical areas, and through numerous dissociations between consciousness and cognitive functions such as attention in humans. Mental imagery paradigms now allow identification of covert awareness in non-responsive subjects. In non-human animals, technological enhancements have clarified the roles of cortical areas and higher-order thalamus for consciousness, and progress has been made in understanding non-vertebrate cognition relevant to possible conscious states. Major advances have also occurred in theories of consciousness and their comparison with available evidence.
Anesthesiology
August 9, 2016
Vincent Bonhomme, Audrey Vanhaudenhuyse, Athena Demertzi et al.
206 citations
Ketamine alters consciousness by disrupting connectivity within and between specific resting-state brain networks, particularly the default mode network (DMn) and salience network (SALn), while leaving sensory and motor networks largely intact. In healthy volunteers given stepwise ketamine infusions until they lost responsiveness, DMn connectivity between the medial prefrontal cortex and other network regions decreased (from 0.20 to 0.07), and the normal anticorrelated activity between the DMn and sensory regions reversed (e.g., right sensory cortex shifted from -0.07 to 0.04). SALn connectivity was also suppressed but nonuniformly. These specific changes, including preserved sensory network connectivity, are shared with propofol-induced unconsciousness.
Proceedings of the National Academy of Sciences
March 26, 2012
Melanie Boly, Vincent Perlbarg, Guillaume Marrelec et al.
201 citations
Consciousness is reduced during nonrapid eye movement (NREM) sleep due to changes in brain function that are still poorly understood. Here, we tested the hypothesis that impaired consciousness during NREM sleep is associated with an increased modularity of brain activity. Cerebral connectivity was quantified in resting-state functional magnetic resonance imaging times series acquired in 13 healthy volunteers during wakefulness and NREM sleep. The analysis revealed a modification of the hierarchical organization of large-scale networks into smaller independent modules during NREM sleep, independently from EEG markers of the slow oscillation. Such modifications in brain connectivity, possibly driven by sleep ultraslow oscillations, could hinder the brain's ability to integrate information and account for decreased consciousness during NREM sleep.
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.
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.
PLoS ONE
February 10, 2023
Lucia Melloni, Liad Mudrik, Michael Pitts et al.
106 citations
An adversarial collaboration between proponents of Global Neuronal Workspace and Integrated Information Theory devised and preregistered two experiments that test contrasting predictions about the location and timing of correlates of visual consciousness. Six theory-impartial laboratories will follow the study protocol using fMRI, M-EEG, and intracranial EEG, with built-in replications between labs and within datasets. The project aims to provide decisive evidence for or against the two theories and clarify the neural footprints of conscious visual perception, while modeling large-scale, collaborative, and open science practice.
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.
Nature
June 1, 2025
Oscar Ferrante, Urszula Gorska-Klimowska, Simon Henin et al.
94 citations
Different theories explain how subjective experience arises from brain activity. An open science adversarial collaboration directly juxtaposed integrated information theory (IIT) and global neuronal workspace theory (GNWT). Human participants (n = 256) viewed suprathreshold stimuli for variable durations while neural activity was measured with fMRI, MEG, and intracranial EEG. Information about conscious content was found in visual, ventrotemporal, and inferior frontal cortex, with sustained responses in occipital and lateral temporal cortex reflecting stimulus duration, and content-specific synchronization between frontal and early visual areas. These results align with some predictions of IIT and GNWT but substantially challenge key tenets of both theories, including a lack of sustained posterior cortex synchronization for IIT and a lack of ignition at stimulus offset and limited prefrontal representation for GNWT.
Journal of Cognitive Neuroscience
May 31, 2017
Lampros Perogamvros, Benjamin Baird, Mitja Seibold et al.
76 citations
Spontaneous thoughts occur during wakefulness, NREM sleep, and REM sleep, and all share activation in the midcingulate cortex. Waking thoughts additionally involve a medial prefrontal region linked to metacognition and have more metacognitive content than sleep thoughts. REM sleep thoughts are more social in content. The findings suggest a core neural substrate for thoughts across behavioral states, with medial prefrontal regions contributing to metacognitive qualities during wake.
Human Brain Mapping
May 8, 2008
Melanie Boly, Christophe Phillips, Evelyne Balteau et al.
73 citations
Variability in how people perceive the same sensory stimulus from one moment to the next may stem from ongoing fluctuations in baseline brain activity. This review examines evidence that activity levels in sensory brain areas before a stimulus predict whether that stimulus will be consciously perceived. The findings are discussed in the context of recent discoveries about the structure of spontaneous BOLD signal fluctuations in the awake human brain, and possible sources of these baseline fluctuations are considered.
Science
March 2, 2007
Adrian M. Owen, Martin R. Coleman, Melanie Boly et al.
72 citations
Functional neuroimaging data indicate that brain activity patterns in a patient diagnosed as vegetative could not have occurred automatically without conscious awareness. The most straightforward explanation is that the patient was consciously aware despite the vegetative state diagnosis.
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.
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.
Neuroscience and biobehavioral reviews
March 1, 2025
Liad Mudrik, Melanie Boly, Stanislas Dehaene et al.
68 citations
In a structured public debate at the 2022 meeting of the Association for the Scientific Study of Consciousness, proponents of five major theories—Global Neuronal Workspace Theory, Higher-Order Theories, Integrated Information Theory, Recurrent Processing Theory, and Predictive Processing—clarified their theories' core mechanisms, foundational premises, and what each theory aims to explain. The discussion revealed more controversy than agreement, particularly on the most basic questions: what consciousness is, how to identify conscious states, and what any adequate theory must account for. Addressing these foundational disagreements is essential for advancing the field and enabling meaningful comparison of competing theories.
Neuroscience of consciousness
January 1, 2021
Francesco Ellia, Jeremiah Hendren, Matteo Grasso et al.
61 citations
Subjective experience can be objectively explained in physical terms by moving beyond cognitive functions and understanding how experience is structured. Integrated information theory provides a framework to account for both the essential properties of every experience and the specific properties that make particular experiences feel the way they do, avoiding the fallacy that only objective properties should be explained by science.
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.
bioRxiv Preprint Server
March 19, 2017
Melanie Boly, Marcello Massimini, Naotsugu Tsychiya et al.
56 citations
preprint
The role of the frontal cortex in consciousness is debated. This perspective critically reviews clinical and neuroimaging evidence on whether the front or back of the cortex specifies conscious contents, and discusses promising research avenues. The authors argue that current evidence does not clearly support a primary role for the frontal cortex in generating conscious experience, pointing instead to posterior regions as more directly involved. They suggest that future research should focus on distinguishing neural correlates of consciousness from prerequisites and consequences.