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.
Frontiers in Human Neuroscience
January 1, 2022
Arnfinn Aamodt, André Sevenius Nilsen, Rune Markhus et al.
29 citations
In a follow-up EEG sleep study, brain signal complexity (Lempel-Ziv complexity, LZC) decreased progressively from wakefulness into deeper non-REM sleep. However, within NREM2 sleep, there was no significant difference in LZC between dream and non-dream awakenings, and no correlation between LZC and subjective ratings of dream vividness, diversity, or perceptual quality. The authors failed to reproduce their earlier finding that posterior LZC increased with more perceptual dream experiences. This raises doubts about whether EEG LZC is a reliable marker of richness of experience within the same sleep stage.
Frontiers in Psychology
April 23, 2021
Arnfinn Aamodt, André Sevenius Nilsen, Benjamin Thürer et al.
24 citations
Signal diversity in EEG recordings, measured by Lempel-Ziv complexity and other metrics, decreases with deeper non-REM sleep stages, consistent with theories linking consciousness to complex cortical dynamics. However, signal diversity did not significantly differ between dreaming and non-dreaming periods within the same sleep stage. A positive correlation was found between Lempel-Ziv complexity over the posterior cortex and the thought-perceptual quality of dream contents, suggesting that specific aspects of dream experience may relate to local cortical signal diversity.
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.
Nature Communications
August 13, 2025
William Wong, Rubén Herzog, Kátia Cristine Andrade et al.
10 citations
A new open database, the DREAM database, combines standardized sleep magneto/electroencephalography (M/EEG) recordings with dream reports from 505 participants across 20 datasets, totaling 2,643 awakenings. Each awakening includes at least 20 seconds of high-resolution sleep EEG (≥100 Hz, ≥2 electrodes) and a classification of the sleeper's reported experience. Analyses showed that reports of conscious experiences during sleep can be predicted from objective EEG features in both REM and NREM sleep. The database aims to overcome limitations of small sample sizes and methodological variability in dream research, enabling larger-scale investigations of the neurocognitive basis of dreaming.
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.
Brain Sciences
September 13, 2024
André Sevenius Nilsen, Johan Frederik Storm, Bjørn Erik Juel
Measures of consciousness based on signal diversity of spontaneous or perturbed EEG are not affected by cognitive load, whereas the P300b event-related potential is. In 12 participants, EEG was recorded during passive attention to sensory stimuli and during a demanding working memory task. The P300b, which reflects conscious awareness of auditory deviance, was significantly reduced by the concurrent memory task. In contrast, several signal diversity measures, including the perturbational complexity index, were unchanged. These findings suggest that signal diversity measures may remain reliable for assessing consciousness in clinical settings where attention, sensory processing, or command following are impaired.
Entropy (Basel, Switzerland)
May 24, 2019
André Sevenius Nilsen, Bjørn Erik Juel, William Marshall
Integrated information theory (IIT) proposes a measure called Phi (Φ) to capture the level of consciousness in a physical system, but calculating Φ is only possible for very small systems. Researchers tested whether several heuristic measures and computational approximations could estimate Φ accurately in small binary networks of 3-6 nodes. They found that some approximations correlated strongly with Φ (r > 0.95) but did not reduce computational demands. Measures of signal complexity, decoder-based integrated information, and state differentiation correlated with the maximum Φ across states. These measures may help estimate a system's capacity for high Φ or identify low-Φ systems, but their applicability to larger or more complex systems remains uncertain.