Neuron
May 15, 2024
Johan F. Storm, P Christiaan Klink, Jaan Aru et al.
108 citations
Consciousness may be explained by multiple, partly compatible theories rather than a single winner. A group of scientists representing different theories argue that various accounts often address different aspects or mechanistic levels of conscious experience, so they do not necessarily contradict each other. Instead, several theories may converge on fundamental neuronal mechanisms and be complementary, allowing multiple perspectives to simultaneously advance understanding. The authors advocate for unifying, integration-oriented approaches that combine valuable elements from diverse theories, an approach that has so far been largely neglected.
PLoS One
November 23, 2020
Nadine Farnes, Bjørn E. Juel, André S. Nilsen et al.
81 citations
In humans, the psychedelic state induced by ketamine is associated with increased diversity and complexity of spontaneous electroencephalography (EEG) signals, but not of evoked EEG responses. This suggests that ketamine's effects on brain dynamics are specific to ongoing, internally generated neural activity rather than to stimulus-driven responses. The finding points to a potential neural marker of altered consciousness under psychedelics.
Frontiers in Human Neuroscience
January 1, 2022
André Sevenius Nilsen, Bjørn E. Juel, Benjamin Thürer et al.
36 citations
Consciousness is more complex than simply labeling states like deep sleep and anesthesia as "unconscious." Investigations show that behavioral signs and subjective reports can be unreliable, challenging traditional beliefs. For instance, individuals in presumed unconscious states may still report experiences, suggesting that 30-50% of patients under general anesthesia retain some awareness. Reevaluating these assumptions could enhance scientific clarity and improve clinical practices, fostering a deeper understanding of consciousness and its disorders. A nuanced approach is essential for future advancements in the field.
May 16, 2023
William Wong, Kátia C. Andrade, Thomas Andrillon et al.
21 citations
preprint
A new open-access database, DREAM, combines sleep magneto/electroencephalography (M/EEG) recordings with standardized dream reports to enable large-scale neurocognitive research on dreaming. The initial release includes 20 datasets from 561 participants and 2649 awakenings, each with at least 20 seconds of high-frequency M/EEG data and a classification of the subject's experience. Analyses demonstrate that features extracted from EEG can predict whether a person reports having had a conscious experience during both REM and NREM sleep. The database aims to overcome the limitations of small sample sizes and methodological variability in dream research, allowing new questions to be addressed at a scale unattainable by individual labs.
Neuroscience of Consciousness
January 1, 2024
André Sevenius Nilsen, Alessandro Arena, Johan F. Storm
10 citations
In rats under propofol, sevoflurane, and ketamine anesthesia, the perturbational complexity index (PCI) and two spontaneous EEG measures—Lempel-Ziv complexity (LZ) and geometric integrated information (ΦG)—best distinguished awake from anesthetized states for propofol and sevoflurane. However, PCI was anti-correlated with spontaneous measures of integrated information, which increased during propofol and sevoflurane anesthesia, contrary to expectations. The divergence suggests anesthesia disrupts global cortico-cortical information transfer, while spontaneous activity suggests the opposite, possibly due to suppressed encoding specificity or driving subcortical projections. Perturbation-based and spontaneous measures may be complementary for studying altered consciousness.
Scientific Reports
September 24, 2025
Imad J. Bajwa, André Sevenius Nilsen, René Skukies et al.
3 citations
People under general anesthesia are often assumed to be unconscious, but some experience dreams. In 20 healthy participants sedated with propofol, EEG was recorded at rest and with TMS perturbations. Participants were repeatedly awakened from deep sedation and asked if they had an experience just before waking. Of 52 attempted awakenings, 24 yielded reports of an experience, 5 reports of no experience, and 23 were unarousable or gave incoherent reports. Two EEG complexity measures—the state transitions perturbational complexity index and single-channel Lempel-Ziv complexity—decreased from awake to sedated states, but did not differ between periods with and without reported experiences within sedation. The authors discuss interpretations and limitations.
PLoS One
January 1, 2024
Nicholas Hagger-Vaughan, Daniel Kolnier, Johan F. Storm
2 citations
A newly described type of depolarising plateau potential (PP) in layer 2/3 pyramidal cells of rat prefrontal cortex slices generates sustained spiking that outlasts the triggering stimulus. Unlike previously known plateau potentials that rely on the apical dendrite, these PPs persist even when the apical dendrite is severed, and are sustained by calcium application only to the soma and basal dendrites. They depend on metabotropic cholinergic or glutamatergic modulation and on TRPC4 and TRPC5 cation channels, requiring external calcium and internal calcium stores but not voltage-gated calcium channels. These PPs may underlie sustained activity important for working memory, access consciousness, and executive functions.
PLoS One
January 1, 2025
Anne S. Fleiner, Daniel Kolnier, Nicholas Hagger-Vaughan et al.
1 citation
Propofol and ketamine, two common general anesthetics, affect consciousness differently—propofol produces a deeply unconscious state with few dreams, while ketamine often leads to vivid dreaming. In rat brain slices of the medial prefrontal cortex, an area linked to conscious access and working memory, researchers added muscarine to mimic an aroused state and recorded electrical activity in layer 2/3 pyramidal cells. Muscarine triggered long-lasting depolarizing plateau potentials and spiking. Pre-incubation with a low dose of propofol reduced these plateau potentials and significantly reduced spiking, whereas a low dose of ketamine appeared to enhance them, though not significantly. A high dose of ketamine suppressed both. The contrasting effects on plateau potentials may relate to the different clinical experiences of dreaming under these drugs.
Scientific Reports
May 2, 2026
Sebastian Halder, Bjørn Erik Juel, Kenneth J Pope et al.
Many EEG-based measures of consciousness, such as spectral slope, Lempel-Ziv complexity, connectivity, alpha peak frequency, and power in canonical frequency bands, fail to detect awareness in awake individuals who are paralyzed by neuromuscular blocking agents. In a study of six healthy volunteers, these measures distinguished awake-unparalysed states from sedated-paralysed states with near-perfect accuracy, but misclassified 7% to 100% of time segments from awake-paralysed subjects as unaware. The findings highlight critical limitations of current EEG-based measures for detecting awareness, particularly in clinical settings where muscle relaxants are used.
bioRxiv Preprint Server
February 14, 2024
Anne S. Fleiner, Daniel Kolnier, Nicholas Hagger-Vaughan et al.
preprint
Propofol and ketamine are both general anaesthetics but produce markedly different states of consciousness. Propofol induces a deeply unconscious state with few or no dream reports, whereas ketamine anaesthesia is frequently followed by reports of vivid dreams. The abstract contrasts these two drugs' effects on awareness and dreaming, highlighting that different anaesthetics can produce distinct subjective experiences even when both cause loss of consciousness.
bioRxiv Preprint Server
March 22, 2019
André S. Nilsen, Bjørn E. Juel, Johan F. Storm
preprint
Measures that distinguish conscious from unconscious brain states may also be influenced by attentional load and cognitive resource use within conscious states. Testing several proposed measures, the study examines whether they are modulated by changes in attention and cognitive demands, which has rarely been tested before. The findings suggest that these measures are not solely markers of consciousness but can vary with attentional load within conscious states.
Frontiers in Neural Circuits
January 1, 2018
William A Phillips, Talis Bachmann, Johan F. Storm
General anesthetics may suppress either the level of consciousness (arousal) or its contents (specific percepts, thoughts, feelings). This distinction is important for understanding both anesthesia and the neural bases of consciousness. Evidence indicates that both level and content depend on apical input to neocortical pyramidal cells, which selectively amplifies relevant signals. What these cells transmit information about can be separated from arousal levels controlled by sub-cortical nuclei and from prioritization set by thalamocortical interactions. The authors hypothesize that when conscious, we have particular directly experienced mental states, and that anesthetics disrupt the subcellular processes that selectively amplify contextually relevant activities.
The Journal of neuroscience : the official journal of the Society for Neuroscience
November 8, 2017
Johan F. Storm, Melanie Boly, Adenauer G. Casali et al.
The mind-body problem—how consciousness arises from brain processes—has long been considered a philosophical puzzle but is now being tackled empirically. This review describes progress since Crick and Koch (1998) proposed searching for the neural correlates of consciousness (NCC). It covers content-specific NCCs, which link particular brain activity to specific experiences, and the full NCC, which supports entire conscious states. The authors discuss methodological advances for isolating conscious experience from enabling functions, suggest that reconsidering the frontal cortex's role may refine NCCs, advocate for objective brain-based measures of consciousness independent of sensory or executive processes, and show how animal studies reveal network phenomena relevant to consciousness mechanisms.
André S. Nilsen, Bjørn E. Juel, Benjamin Thürer et al.
preprint
A systematic review of 255 EEG-based measures of consciousness found that signal diversity and event-related potential measures are the most consistent for distinguishing conscious from unconscious brain states. Spectral entropy, Lempel Ziv complexity, and spectral edge frequency emerged as the most practical, consistent, and reproducible measures. However, because most studies relied on behavioral assessments rather than subjective reports, the true presence or absence of phenomenological experience remains uncertain, limiting the conclusions that can be drawn. The review provides detailed categorizations to guide future research.