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.
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.
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.
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.
arXiv Preprint Archive
October 7, 2025
Maria V. Sanchez-Vives, Arnau Manasanch, Andrea Pigorini et al.
The cerebral cortex generates diverse patterns of activity that shift across brain states such as sleep, wakefulness, anesthesia, and disorders of consciousness, yet a unified definition of brain states remains elusive. This review focuses on two extremes: synchronous states, which predominantly underlie unconsciousness, and asynchronous states, which predominantly underlie consciousness, though exceptions exist. The authors integrate data across levels from local circuits to whole-brain dynamics, examining properties like cortical complexity, functional connectivity, synchronization, wave propagation, and excitatory-inhibitory balance. They make experimental and clinical data, as well as computational models at micro-, meso-, and macrocortical levels, available to readers.
arXiv Preprint Archive
December 30, 2024
William G. P. Mayner, Bjørn Erik Juel, Giulio Tononi
Integrated information theory (IIT) holds that consciousness arises from a maximally irreducible complex of units whose cause-effect structure fully accounts for the quality of experience. The feeling of an experience is its intrinsic meaning for the subject, whether occurring in a dream or triggered by the environment. This work extends IIT to characterize the relationship between intrinsic meaning, extrinsic stimuli, and causal processes, using a simple sensory-hierarchy model. Perception is framed as a structured interpretation in which a stimulus merely triggers the complex's state, and the structure comes from the complex's intrinsic connectivity. Perceptual differentiation—the richness of structures triggered by representative stimulus sequences—quantifies how meaningful different environments are to a complex, reflecting the match between intrinsic meanings and environmental causal processes.
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.