Bjørn Erik Juel

• Halder, Sebastian; Juel, Bjørn Erik; Pope, Kenneth J.; Hardy, Andrew; Willoughby, John O. & Storm, Johan Frederik (2026). An experimental study of the effect of neuromuscular blockade on EEG-based measures of awareness. Scientific Reports. doi: 10.1038/s41598-026-50911-6. Full text in Research Archive Show summary

  Both basic and clinical consciousness research aims to find objective measures that reliably distinguish conscious from unconscious brain states. Electroencephalogram (EEG) measures are widely used, although they may be affected by interference from electrical signals such as those generated by muscles. To assess this source of error, we investigated the impact of neuromuscular blockade (NMB) on proposed measures of awareness (spectral slope, Lempel–Ziv complexity (LZc), connectivity, alpha peak frequency, power in canonical EEG frequency bands) computed from spontaneous high-density EEG recorded from six healthy volunteers in three different conditions: (1) awake-unparalysed (normal wakefulness), (2) awake-paralysed (complete paralysis caused by neuromuscular blocking agent (NMBA)), and (3) sedated-paralysed (deep sedation with propofol, with paralysis by NMBA). The measures we investigated distinguished awake-unparalysed states from sedated-paralysed with close to perfect accuracy in accordance with past findings. However, our analysis revealed a serious failure of most measures to recognise the awake-paralysed condition as an aware state. Errors ranged from 7% of awake-paralysed time segments predicted as unaware (using alpha power) to 100% (using LZc). Using a unique high-density EEG data set, this study clearly demonstrates that many EEG-based measures fail to recognise awareness in awake subjects under the influence of muscle relaxants. These results highlight critical limitations of current EEG-based measures at detecting awareness.

• Destexhe, Alain; Goldman, Jennifer S; Tort-Colet, Nuria; Roques, Axel; Fousek, Jan & Petkoski, Spase [Show all 35 contributors for this article] (2025). State-dependent brain responsiveness, from local circuits to the whole brain. eLIFE. 14, p. 1–36. doi: 10.7554/elife.108768.1. Full text in Research Archive Show summary

  The objective of this paper is to review physiological and computational aspects of the responsiveness of the cerebral cortex to stimulation, and how responsiveness depends on the state of the system. This correspondence between brain state and brain responsiveness (statedependent responses) is outlined at different scales from the cellular and circuit level, to the mesoscale and macroscale level. At each scale, we review how quantitative methods can be used to characterize network states based on brain responses, such as the Perturbational Complexity Index (PCI). This description will compare data and models, systematically and at multiple scales, with a focus on the mechanisms that explain how brain responses depend on brain states.

• Bajwa, Imad Javaid; Nilsen, Andre Sevenius; Skukies, René Sebastian; Aamodt, Arnfinn; Ernst, Gernot Walter & Storm, Johan Frederik [Show all 7 contributors for this article] (2025). A repeated awakening study exploring the capacity of complexity measures to capture dreaming during propofol sedation | Scientific Reports. Scientific Reports. 15, p. 1–12. doi: 10.1038/s41598-025-12695-z. Full text in Research Archive Show summary

  Patients undergoing general anesthesia are often assumed to be unconscious. However, it is known that conscious experiences in the form of dreams occur even in unresponsive states induced by anesthetics. Here, we recorded resting state electroencephalography (EEG) as well as EEG combined with TMS perturbations in 20 healthy participants during propofol sedation. Participants were repeatedly awoken from deep sedation and asked immediately whether they had experiences just before waking up and what they experienced. Out of the 52 attempted awakenings in this study, 24 produced reports of having had an experience, while there were 5 reports of no experience. In the remaining 23 attempts, the subject was either unarousable or the report too incoherent to provide information about their experience prior to awakening. We then tested whether two different consciousness measures based on EEG complexity—the state transitions perturbational complexity index (PCIst) and single-channel Lempel-Ziv complexity (LZc)—differed between awakenings with and without experience. While our study confirms earlier findings that the EEG complexity measures significantly decrease from the awake state to the sedated state, we find no evidence that these measures differ between periods associated with reports of dreaming and non-dreaming, within the sedated state. A few interpretations and limitations are discussed.

• Hov, Laila; Førde, Reidun; Steindal, Simen Alexander; Myrhaug, Hilde Tinderholt; Skogestad, Ingrid Johansen & Juel, Bjørn Erik (2025). Perspectives, attitudes and experiences of introducing noninvasive medical technologies in end-of-life care: a scoping review. BMC Palliative Care. 24(1), p. 1–7. doi: 10.1186/s12904-025-01890-4. Full text in Research Archive Show summary

  Abstract Background There is a strong tradition for withdrawing medical equipment from patients receiving end-of-life (EOL) care. However, the introduction of new noninvasive medical equipment could be acceptable provided that it improves the quality of care and patient comfort. Objectives We aimed to systematically map published studies of the perspectives, attitudes and experiences of health care professionals, dying patients, and their next of kin, about introducing noninvasive medical technology in end-of-life care. Design We conducted a scoping review. On January 27, 2025, systematic searches of five databases were carried out (Medline (EBSCO), CINAHL, Embase, Academic Search Elite, and Cochrane Library CDSR). Inclusion criteria were empirical studies published in English or Scandinavian languages. We searched for qualitative, quantitative or mixed method studies focusing on perspectives on, experiences of and attitudes toward introducing noninvasive medical technologies in end-of-life care from the view of health care professionals, dying patients, and their next of kin. Three pairs of researchers independently assessed potential eligibility and data extraction. Data would be summarized qualitatively. Results The searches yielded 3288 unique articles, 3194 of which were excluded following an initial screening. Among the remaining 94 articles, none satisfied our inclusion criteria. Thus, we found no empirical articles addressing perspectives on, attitudes toward, or experiences with the use of noninvasive medical technology in end-of-life care. Conclusions Empirical research exploring the perspectives on, attitudes toward, and experiences of, and use of noninvasive medical technology in end-of-life care is needed. This is important for understanding when and how it is feasible, useful, and ethical to introduce such technologies in the terminal phase of palliative care.

• Bajwa, Imad Javaid; Nilsen, Andre Sevenius; Skukies, René Sebastian; Aamodt, Arnfinn; Ernst, Gernot Walter & Storm, Johan Frederik [Show all 7 contributors for this article] (2025). A repeated awakening study exploring the capacity of complexity measures to capture dreaming during propofol sedation. Scientific Reports. 15. doi: 10.1038/s41598-025-12695-z. Full text in Research Archive Show summary

  Patients undergoing general anesthesia are often assumed to be unconscious. However, it is known that conscious experiences in the form of dreams occur even in unresponsive states induced by anesthetics. Here, we recorded resting state electroencephalography (EEG) as well as EEG combined with TMS perturbations in 20 healthy participants during propofol sedation. Participants were repeatedly awoken from deep sedation and asked immediately whether they had experiences just before waking up and what they experienced. Out of the 52 attempted awakenings in this study, 24 produced reports of having had an experience, while there were 5 reports of no experience. In the remaining 23 attempts, the subject was either unarousable or the report too incoherent to provide information about their experience prior to awakening. We then tested whether two different consciousness measures based on EEG complexity—the state transitions perturbational complexity index (PCIst) and single-channel Lempel-Ziv complexity (LZc)—differed between awakenings with and without experience. While our study confirms earlier findings that the EEG complexity measures significantly decrease from the awake state to the sedated state, we find no evidence that these measures differ between periods associated with reports of dreaming and non-dreaming, within the sedated state. A few interpretations and limitations are discussed.

• Wong, William; Herzog, Ruben; Andrade, Kátia Cristine; Andrillon, Thomas; Araujo, Draulio Barros de & Arnulf, Isabelle [Show all 53 contributors for this article] (2025). A dream EEG and mentation database. Nature Communications. 16. doi: 10.1038/s41467-025-61945-1. Full text in Research Archive Show summary

  Magneto/electroencephalography (M/EEG) studies of dreaming are an essential paradigm in the investigation of neurocognitive processes of human consciousness during sleep, but they are limited by the number of observations that can be collected per study. Dream research also involves substantial methodological and conceptual variability, which poses problems for the integration of results. To address these issues, here we present the DREAM database—an expanding collection of standardized datasets on human sleep M/EEG combined with dream report data—with an initial release comprising 20 datasets, 505 participants, and 2643 awakenings. Each awakening consists, at minimum, of sleep M/EEG ( ≥ 20 s, ≥100 Hz, ≥2 electrodes) up to the time of waking and a standardized dream report classification of the subject’s experience during sleep. We observed that reports of conscious experiences can be predicted with objective features extracted from EEG recordings in both Rapid Eye Movement (REM) and non-REM (NREM) sleep. We also provide several examples of analyses, showcasing the database’s high potential in paving the way for new research questions at a scale beyond the capacity of any single research group.

• Nilsen, Andre Sevenius; Storm, Johan Frederik & Juel, Bjørn Erik (2024). Does Cognitive Load Affect Measures of Consciousness? Brain Sciences. 14(9). doi: 10.3390/brainsci14090919. Full text in Research Archive Show summary

  Background: Developing and testing methods for reliably measuring the state of consciousness of individuals is important for both basic research and clinical purposes. In recent years, several promising measures of consciousness, grounded in theoretical developments, have been proposed. However, the degrees to which these measures are affected by changes in brain activity that are not related to changes in the degree of consciousness has not been well tested. In this study, we examined whether several of these measures are modulated by the loading of cognitive resources. Methods: We recorded electroencephalography (EEG) from 12 participants in two conditions: (1) while passively attending to sensory stimuli related to the measures and (2) during increased cognitive load consisting of a demanding working memory task. We investigated whether a set of proposed objective EEG-based measures of consciousness differed between the passive and the cognitively demanding conditions. Results: The P300b event-related potential (sensitive to conscious awareness of deviance from an expected pattern in auditory stimuli) was significantly affected by concurrent performance on a working memory task, whereas various measures based on signal diversity of spontaneous and perturbed EEG were not. Conclusion: Because signal diversity-based measures of spontaneous or perturbed EEG are not sensitive to the degree of cognitive load, we suggest that these measures may be used in clinical situations where attention, sensory processing, or command following might be impaired.

• Albantakis, Larissa; Barbosa, Leonardo; Findlay, Graham; Grasso, Matteo; Haun, Andrew M. & Marshall, William [Show all 16 contributors for this article] (2023). Integrated information theory (IIT) 4.0: Formulating the properties of phenomenal existence in physical terms. PLoS Computational Biology. ISSN 1553-734X. 19(10). doi: 10.1371/journal.pcbi.1011465. Full text in Research Archive Show summary

  This paper presents Integrated Information Theory (IIT) 4.0. IIT aims to account for the properties of experience in physical (operational) terms. It identifies the essential properties of experience (axioms), infers the necessary and sufficient properties that its substrate must satisfy (postulates), and expresses them in mathematical terms. In principle, the postulates can be applied to any system of units in a state to determine whether it is conscious, to what degree, and in what way. IIT offers a parsimonious explanation of empirical evidence, makes testable predictions concerning both the presence and the quality of experience, and permits inferences and extrapolations. IIT 4.0 incorporates several developments of the past ten years, including a more accurate formulation of the axioms as postulates and mathematical expressions, the introduction of a unique measure of intrinsic information that is consistent with the postulates, and an explicit assessment of causal relations. By fully unfolding a system’s irreducible cause–effect power, the distinctions and relations specified by a substrate can account for the quality of experience.

• Aamodt, Arnfinn; Nilsen, Andre Sevenius; Markhus, Rune; Kusztor, Aniko; Hasanzadehmoghadam, Fatemeh & Kauppi, Nils [Show all 9 contributors for this article] (2023). EEG Lempel-Ziv complexity varies with sleep stage, but does not seem to track dream experience. Frontiers in Human Neuroscience. 16, p. 1–19. doi: 10.3389/fnhum.2022.987714. Full text in Research Archive Show summary

  In a recent electroencephalography (EEG) sleep study inspired by complexity theories of consciousness, we found that multi-channel signal diversity progressively decreased from wakefulness to slow wave sleep, but failed to find any significant difference between dreaming and non-dreaming awakenings within the same sleep stage (NREM2). However, we did find that multi-channel Lempel-Ziv complexity (LZC) measured over the posterior cortex increased with more perceptual ratings of NREM2 dream experience along a thought-perceptual axis. In this follow-up study, we re-tested our previous findings, using a slightly different approach. Partial sleep-deprivation was followed by evening sleep experiments, with repeated awakenings and immediate dream reports. Participants reported whether they had been dreaming, and were asked to rate how diverse, vivid, perceptual, and thought-like the contents of their dreams were. High density (64 channel) EEG was recorded throughout the experiment, and mean single-channel LZC was calculated for each 30 s sleep epoch. LZC progressively decreased with depth of non-REM sleep. Surprisingly, estimated marginal mean LZC was slightly higher for NREM1 than for wakefulness, but the difference did not remain significant after adjusting for multiple comparisons. We found no significant difference in LZC between dream and non-dream awakenings, nor any significant relationship between LZC and subjective ratings of dream experience, within the same sleep stage (NREM2). The failure to reproduce our own previous finding of a positive correlation between posterior LZC and more perceptual dream experiences, or to find any other correlation between brain signal complexity and subjective experience within NREM2 sleep, raises the question of whether EEG LZC is really a reliable correlate of richness of experience as such, within the same sleep stage.

• Nilsen, Andre Sevenius; Juel, Bjørn Erik; Thürer, Benjamin; Aamodt, Arnfinn & Storm, Johan Frederik (2022). Are we really unconscious in “unconscious” states? Common assumptions revisited. Frontiers in Human Neuroscience. 16. doi: 10.3389/fnhum.2022.987051. Full text in Research Archive Show summary

  In the field of consciousness science, there is a tradition to categorize certain states such as slow-wave non-REM sleep and deep general anesthesia as “unconscious”. While this categorization seems reasonable at first glance, careful investigations have revealed that it is not so simple. Given that (1) behavioral signs of (un-)consciousness can be unreliable, (2) subjective reports of (un-)consciousness can be unreliable, and, (3) states presumed to be unconscious are not always devoid of reported experience, there are reasons to reexamine our traditional assumptions about “states of unconsciousness”. While these issues are not novel, and may be partly semantic, they have implications both for scientific progress and clinical practice. We suggest that focusing on approaches that provide a more pragmatic and nuanced characterization of different experimental conditions may promote clarity in the field going forward, and help us build stronger foundations for future studies.

• Arena, Alessandro; Juel, Bjørn Erik; Comolatti, Renzo; Thon, Sarah & Storm, Johan Frederik (2021). Capacity for consciousness under ketamine anaesthesia is selectively associated with activity in posteromedial cortex in rats. Neuroscience of Consciousness. 2022(1), p. 1–15. doi: 10.1093/nc/niac004. Full text in Research Archive Show summary

  It remains unclear how specific cortical regions contribute to the brain’s overall capacity for consciousness. Clarifying this could help distinguish between theories of consciousness. Here, we investigate the association between markers of regionally specific (de)activation and the brain’s overall capacity for consciousness. We recorded electroencephalographic responses to cortical electrical stimulation in six rats and computed Perturbational Complexity Index state-transition (PCIST), which has been extensively validated as an index of the capacity for consciousness in humans. We also estimated the balance between activation and inhibition of specific cortical areas with the ratio between high and low frequency power from spontaneous electroencephalographic activity at each electrode. We repeated these measurements during wakefulness, and during two levels of ketamine anaesthesia: with the minimal dose needed to induce behavioural unresponsiveness and twice this dose. We found that PCIST was only slightly reduced from wakefulness to light ketamine anaesthesia, but dropped significantly with deeper anaesthesia. The high-dose effect was selectively associated with reduced high frequency/low frequency ratio in the posteromedial cortex, which strongly correlated with PCIST. Conversely, behavioural unresponsiveness induced by light ketamine anaesthesia was associated with similar spectral changes in frontal, but not posterior cortical regions. Thus, activity in the posteromedial cortex correlates with the capacity for consciousness, as assessed by PCIST, during different depths of ketamine anaesthesia, in rats, independently of behaviour. These results are discussed in relation to different theories of consciousness.

• Aamodt, Arnfinn; Nilsen, Andre Sevenius; Thürer, Benjamin; Moghadam, Fatemeh Hasanzadeh; Kauppi, Nils & Juel, Bjørn Erik [Show all 7 contributors for this article] (2021). EEG Signal Diversity Varies With Sleep Stage and Aspects of Dream Experience. Frontiers in Psychology. 12. doi: 10.3389/fpsyg.2021.655884. Full text in Research Archive Show summary

  Several theories link consciousness to complex cortical dynamics, as suggested by comparison of brain signal diversity between conscious states and states where consciousness is lost or reduced. In particular, Lempel-Ziv complexity, amplitude coalition entropy and synchrony coalition entropy distinguish wakefulness and REM sleep from deep sleep and anesthesia, and are elevated in psychedelic states, reported to increase the range and vividness of conscious contents. Some studies have even found correlations between complexity measures and facets of self-reported experience. As suggested by integrated information theory and the entropic brain hypothesis, measures of differentiation and signal diversity may therefore be measurable correlates of consciousness and phenomenological richness. Inspired by these ideas, we tested three hypotheses about EEG signal diversity related to sleep and dreaming. First, diversity should decrease with successively deeper stages of non-REM sleep. Second, signal diversity within the same sleep stage should be higher for periods of dreaming vs. non-dreaming. Third, specific aspects of dream contents should correlate with signal diversity in corresponding cortical regions. We employed a repeated awakening paradigm in sleep deprived healthy volunteers, with immediate dream report and rating of dream content along a thought-perceptual axis, from exclusively thought-like to exclusively perceptual. Generalized linear mixed models were used to assess how signal diversity varied with sleep stage, dreaming and thought-perceptual rating. Signal diversity decreased with sleep depth, but was not significantly different between dreaming and non-dreaming, even though there was a significant positive correlation between Lempel-Ziv complexity of EEG recorded over the posterior cortex and thought-perceptual ratings of dream contents.

• Arena, Alessandro; Juel, Bjørn Erik; Comolatti, Renzo; Thon, Sarah Kriebel & Storm, Johan (2021). Does the posteromedial cortex play a primary role for the capacity for consciousness in rats? BioRxiv. ISSN 0362-4331. doi: 10.1101/2021.01.22.427747. Full text in Research Archive Show summary

  It remains unclear how specific cortical regions contribute to the brain’s overall capacity for consciousness. Clarifying this could help distinguish between theories of consciousness. Here, we investigate the association between markers of regionally specific (de)activation and the brain’s overall capacity for consciousness. We recorded electroencephalographic (EEG) responses to cortical electrical stimulation in 6 rats, and computed Perturbational Complexity Index state-transition (PCIST), which has been extensively validated as an index of the capacity for consciousness in humans. We also estimated the balance between activation and inhibition of specific cortical areas with the ratio between high and low frequency power (HF/LF) from spontaneous EEG activity at each electrode. We repeated these measurements during wakefulness, and under the influence of ketamine anaesthesia at two doses: the minimal dose needed to induce behavioural unresponsiveness and twice this dose. We found that PCIST was only slightly reduced from wakefulness to light ketamine anaesthesia, but dropped significantly down with deeper anaesthesia. The high-dose effect was selectively associated with reduced HF/LF ratio in the posteromedial cortex, which strongly correlated with PCIST. Conversely, behavioural unresponsiveness induced by light ketamine anaesthesia, was associated with similar spectral changes in frontal, but not posterior cortical regions. These findings seem to support the claim that the posteromedial cortex may play a primary role for the capacity for consciousness. Such region-specific associations between cortical activation and the overall capacity for consciousness must be accounted for by theories of consciousness.

• Nilsen, Andre Sevenius; Juel, Bjørn Erik; Farnes, Nadine; Romundstad, Luis Georg & Storm, Johan Frederik (2020). Behavioral effects of sub-anesthetic ketamine in a go/no-go task. Journal of Psychedelic Studies. 4(3), p. 156–162. doi: 10.1556/2054.2020.00126. Full text in Research Archive Show summary

  Background and aims While psychedelic agents are known to have powerful, but largely unexplained, effects on contents of consciousness, there is an increasing interest in the potential clinical usefulness of such drugs for therapy, and legalization is discussed in some countries. Thus, it is relevant to study the effects of psychedelic compounds not only on experience, but also on behavioral performance. Methods Seven healthy participants performed a motor response inhibition task before, during, and after sub-anesthetic doses of intravenously administered ketamine. The infusion rate was individually adjusted to produce noticeable subjective psychedelic effects. Results We observed no statistically significant impact of sub-anesthetic ketamine on reaction times, omission errors, or post error slowing, relative to the preceding drug-free condition. However, we did observe significant correlations between performance impairment and self-reported, subjective altered states of consciousness, specifically experience of “anxiety” and “complex imagery.” Conclusions Considering the limited number of participants and large variation in strength of self-reported experiences, further studies with wider ranges of ketamine doses and behavioral tasks are needed to determine the presence and strength of potential behavioral effects.

• Farnes, Nadine; Juel, Bjørn Erik; Nilsen, Andre Sevenius; Romundstad, Luis Georg & Storm, Johan Frederik (2020). Increased signal diversity/complexity of spontaneous EEG, but not evoked EEG responses, in ketamine-induced psychedelic state in humans. PLOS ONE. 15:e024056(11), p. 1–21. doi: 10.1371/journal.pone.0242056. Full text in Research Archive Show summary

  Objective How and to what extent electrical brain activity is affected in pharmacologically altered states of consciousness, where it is mainly the phenomenological content rather than the level of consciousness that is altered, is not well understood. An example is the moderately psychedelic state caused by low doses of ketamine. Therefore, we investigated whether and how measures of evoked and spontaneous electroencephalographic (EEG) signal diversity are altered by sub-anaesthetic levels of ketamine compared to normal wakefulness, and how these measures relate to subjective assessments of consciousness. Methods High-density electroencephalography (EEG, 62 channels) was used to record spontaneous brain activity and responses evoked by transcranial magnetic stimulation (TMS) in 10 healthy volunteers before and after administration of sub-anaesthetic doses of ketamine in an open-label within-subject design. Evoked signal diversity was assessed using the perturbational complexity index (PCI), calculated from the global EEG responses to local TMS perturbations. Signal diversity of spontaneous EEG, with eyes open and eyes closed, was assessed by Lempel Ziv complexity (LZc), amplitude coalition entropy (ACE), and synchrony coalition entropy (SCE). Results Although no significant difference was found in the index of TMS-evoked complexity (PCI) between the sub-anaesthetic ketamine condition and normal wakefulness, all the three measures of spontaneous EEG signal diversity showed significantly increased values in the sub-anaesthetic ketamine condition. This increase in signal diversity also correlated with subjective assessment of altered states of consciousness. Moreover, spontaneous signal diversity was significantly higher when participants had eyes open compared to eyes closed, both during normal wakefulness and during influence of sub-anaesthetic ketamine doses. Conclusion The results suggest that PCI and spontaneous signal diversity may be complementary and potentially measure different aspects of consciousness. Thus, our results seem compatible with PCI being indicative of the brain’s ability to sustain consciousness, as indicated by previous research, while it is possible that spontaneous EEG signal diversity may be indicative of the complexity of conscious content. The observed sensitivity of the latter measures to visual input seems to support such an interpretation. Thus, sub-anaesthetic ketamine may increase the complexity of both the conscious content (experience) and the brain activity underlying it, while the level, degree, or general capacity of consciousness remains largely unaffected.

• Halder, Sebastian; Juel, Bjørn Erik; Nilsen, Andre Sevenius; Raghavan, L Venkat & Storm, Johan Frederik (2020). Changes in measures of consciousness during anaesthesia of one hemisphere (Wada test). NeuroImage. ISSN 1053-8119. 226. doi: 10.1016/j.neuroimage.2020.117566. Full text in Research Archive Show summary

  Background In the Wada test, one hemisphere is selectively anaesthetised by unilateral intracarotid injection of a fast-acting anaesthetic agent. This gives a unique opportunity to observe the functions and physiological activity of one hemisphere while anaesthetising the other, allowing direct comparisons between brain states and hemispheres that are not possible in any other setting. Aim To test whether potential measures of consciousness would be affected by selective anaesthesia of one hemisphere, and reliably distinguish the states of the anesthetised and non-anesthetised hemispheres. Methods We analysed EEG data from 7 patients undergoing Wada-tests in preparation for neurosurgery and computed several measures reported to correlate with the state of consciousness: power spectral density, functional connectivity, and measures of signal diversity. These measures were compared between conditions (normal rest vs. unilateral anaesthesia) and hemispheres (injected vs. non-injected), and used with a support vector machine to classify the state and site of injection objectively from individual patient's recordings. Results Although brain function, assessed behaviourally, appeared to be substantially altered only on the injected side, we found large bilateral changes in power spectral density for all frequency bands tested, and functional connectivity changed significantly both between and within both hemispheres. Surprisingly, we found no statistically significant differences in the measures of signal diversity between hemispheres or states, for the group of 7 patients, although 4 of the individual patients showed a significant decrease in signal diversity on the injected side. Nevertheless, including signal diversity measures improved the classification results, indicating that these measures carry at least some non-redundant information about the condition and injection site. We propose that several of these results may be explained by conduction of activity, via the corpus callosum, from the injected to the contralateral hemisphere and vice versa, without substantially affecting the function of the receiving hemisphere, thus reflecting what we call “cross-state unreceptiveness”.

• Juel, Bjørn Erik; Romundstad, Luis Georg; Storm, Johan Frederik & Larsson, Pål Gunnar (2020). Validation of a new approach for distinguishing anesthetized from awake state in patients using directed transfer function applied to raw EEG. Journal of clinical monitoring and computing. ISSN 1387-1307. p. 1–14. doi: 10.1007/s10877-020-00603-x. Full text in Research Archive Show summary

  We test whether a measure based on the directed transfer function (DTF) calculated from short segments of electroencephalography (EEG) time-series can be used to monitor the state of the patients also during sevoflurane anesthesia as it can for patients undergoing propofol anesthesia. We collected and analyzed 25-channel EEG from 7 patients (3 females, ages 41–56 years) undergoing surgical anesthesia with sevoflurane, and quantified the sensor space directed connectivity for every 1-s epoch using DTF. The resulting connectivity parameters were compared to corresponding parameters from our previous study (n = 8, patients anesthetized with propofol and remifentanil, but otherwise using a similar protocol). Statistical comparisons between and within studies were done using permutation statistics, a data driven algorithm based on the DTF-parameters was employed to classify the epochs as coming from awake or anesthetized state. According to results of the permutation tests, DTF-parameter topographies were significantly different between the awake and anesthesia state at the group level. However, the topographies were not significantly different when comparing results computed from sevoflurane and propofol data, neither in the awake nor in anesthetized state. Optimizing the algorithm for simultaneously having high sensitivity and specificity in classification yielded an accuracy of 95.1% (SE = 0.96%), with sensitivity of 98.4% (SE = 0.80%) and specificity of 94.8% (SE = 0.10%). These findings indicate that the DTF changes in a similar manner when humans undergo general anesthesia caused by two distinct anesthetic agents with different molecular mechanisms of action.

• Nilsen, Andre Sevenius; Juel, Bjørn Erik; Thürer, Benjamin & Storm, Johan Frederik (2020). Proposed EEG measures of consciousness: asystematic, comparative review. PsyArXiv. doi: 10.31234/osf.io/sjm4a. Full text in Research Archive
• Juel, Bjørn Erik; Comolatti, Renzo; Albantakis, Larissa & Tononi, Giulio (2019). When is an action caused from within? Quantifying the causal chain leading to actions in simulated agents. ALIFE : Proceedings of the Artificial Life Conference. doi: 10.1162/isal_a_00207. Full text in Research Archive Show summary

  An agent’s actions can be influenced by external factors through the inputs it receives from the environment, as well as internal factors, such as memories or intrinsic preferences. The extent to which an agent’s actions are “caused from within”, as opposed to being externally driven, should depend on its sensor capacity as well as environmental demands for memory and context-dependent behavior. Here, we test this hypothesis using simulated agents (“animats”), equipped with small adaptive Markov Brains (MB) that evolve to solve a perceptual-categorization task under conditions varied with regards to the agents’ sensor capacity and task difficulty. Using a novel formalism developed to identify and quantify the actual causes of occurrences (“what caused what?”) in complex networks, we evaluate the direct causes of the animats’ actions. In addition, we extend this framework to trace the causal chain (“causes of causes”) leading to an animat’s actions back in time, and compare the obtained spatio-temporal causal history across task conditions. We found that measures quantifying the extent to which an animat’s actions are caused by internal factors (as opposed to being driven by the environment through its sensors) varied consistently with defining aspects of the task conditions they evolved to thrive in.

• Nilsen, Andre Sevenius; Juel, Bjørn Erik & Marshall, William (2019). Evaluating approximations and heuristic measures of integrated information. Entropy. 21(5), p. 1–23. doi: 10.3390/e21050525. Full text in Research Archive Show summary

  Integrated information theory (IIT) proposes a measure of integrated information, termed Phi (Φ), to capture the level of consciousness of a physical system in a given state. Unfortunately, calculating Φ itself is currently possible only for very small model systems and far from computable for the kinds of system typically associated with consciousness (brains). Here, we considered several proposed heuristic measures and computational approximations, some of which can be applied to larger systems, and tested if they correlate well with Φ. While these measures and approximations capture intuitions underlying IIT and some have had success in practical applications, it has not been shown that they actually quantify the type of integrated information specified by the latest version of IIT and, thus, whether they can be used to test the theory. In this study, we evaluated these approximations and heuristic measures considering how well they estimated the Φ values of model systems and not on the basis of practical or clinical considerations. To do this, we simulated networks consisting of 3–6 binary linear threshold nodes randomly connected with excitatory and inhibitory connections. For each system, we then constructed the system’s state transition probability matrix (TPM) and generated observed data over time from all possible initial conditions. We then calculated Φ, approximations to Φ, and measures based on state differentiation, coalition entropy, state uniqueness, and integrated information. Our findings suggest that Φ can be approximated closely in small binary systems by using one or more of the readily available approximations (r > 0.95) but without major reductions in computational demands. Furthermore, the maximum value of Φ across states (a state-independent quantity) correlated strongly with measures of signal complexity (LZ, rs = 0.722), decoder-based integrated information (Φ*, rs = 0.816), and state differentiation (D1, rs = 0.827). These measures could allow for the efficient estimation of a system’s capacity for high Φ or function as accurate predictors of low- (but not high-)Φ systems. While it is uncertain whether the results extend to larger systems or systems with other dynamics, we stress the importance that measures aimed at being practical alternatives to Φ be, at a minimum, rigorously tested in an environment where the ground truth can be established.

• Kusztor, Aniko; Raud, Liisa; Juel, Bjørn Erik; Nilsen, Andre Sevenius; Storm, Johan Frederik & Huster, Rene (2019). Sleep deprivation differentially affects subcomponents of cognitive control. Sleep. ISSN 0161-8105. 42(4). doi: 10.1093/sleep/zsz016. Full text in Research Archive
• Juel, Bjørn Erik; Romundstad, Luis Georg; Kolstad, Frode; Storm, Johan Frederik & Larsson, Pål Gunnar (2018). Distinguishing anesthetized from awake state in patients: A new approach using one second segments of raw EEG. Frontiers in Human Neuroscience. 12:40, p. 1–14. doi: 10.3389/fnhum.2018.00040. Full text in Research Archive Show summary

  Objective: The objective of this study was to test whether properties of 1-s segments of spontaneous scalp EEG activity can be used to automatically distinguish the awake state from the anesthetized state in patients undergoing general propofol anesthesia. Methods: Twenty five channel EEG was recorded from 10 patients undergoing general intravenous propofol anesthesia with remifentanil during anterior cervical discectomy and fusion. From this, we extracted properties of the EEG by applying the Directed Transfer Function (DTF) directly to every 1-s segment of the raw EEG signal. The extracted properties were used to develop a data-driven classification algorithm to categorize patients as “anesthetized” or “awake” for every 1-s segment of raw EEG. Results: The properties of the EEG signal were significantly different in the awake and anesthetized states for at least 8 of the 25 channels (p < 0.05, Bonferroni corrected Wilcoxon rank-sum tests). Using these differences, our algorithms achieved classification accuracies of 95.9%. Conclusion: Properties of the DTF calculated from 1-s segments of raw EEG can be used to reliably classify whether the patients undergoing general anesthesia with propofol and remifentanil were awake or anesthetized. Significance: This method may be useful for developing automatic real-time monitors of anesthesia.

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• Juel, Bjørn Erik (2025). 2000 mennesker døde: Hevder de så dette. [Journal]. Dagbladet. doi: https:/www.dagbladet.no/tema/2000-mennesker-dode-hevder-de-sa-dette/83675631. Full text in Research Archive Show summary

  Hva skjer etter døden? Dagbladet har sett på forskningen, snakket med forskere og tar deg med så langt det er mulig på den andre siden. I en av studiene snakket forskerne med flere som har vært klinisk døde - og nå svarer de: Dette skal de ha sett.

• Juel, Bjørn Erik (2025). Ferievikarene - bevissthet. [Radio]. NRK. doi: https:/radio.nrk.no/serie/ferievikarene/sesong/202507/PLUV16000725. Full text in Research Archive
• Aas, Kristina; Aass, Hanne Cecilia; Jemterud, Torkild; Juel, Bjørn Erik & Storm, Johan Frederik (2025). Hvorfor drømmer vi? [Radio]. NRK. doi: https:/radio.nrk.no/podkast/abels_taarn/l_8028544e-1ce4-4462-a854-4e1ce454629b. Full text in Research Archive Show summary

  Hva er det som egentlig skjer i hjernen når vi drømmer? Hvordan kan drømmer føles så ekte, og hvorfor drømmer vi i det hele tatt? I denne miniserien tar vi et dypdykk i drømmenes verden.

• Sandtorv, Alexander Harald; Schau, Kristopher & Juel, Bjørn Erik (2025). Afantasi - «når jeg lukker øynene er det svart». doi: https:/shows.acast.com/tingenes-tilstand/episodes/afantasi-nar-jeg-lukker-yene-er-det-svart. Full text in Research Archive Show summary

  Vi satt igjen med flere spørsmål enn svar sist vi var inne på temaet, derfor har vi hanket inn en gjest som SELV har afantasi - fysiker og hjerneforsker Bjørn Erik Juel. Drømmer han? Får han sanger på hjernen? Hvordan er det med hukommelsen? Og hva med den indre monologen?

• Schau, Kristopher & Juel, Bjørn Erik (2025). Bevissthet. doi: https:/shows.acast.com/rekommandert/episodes/bevissthet. Full text in Research Archive Show summary

  Fysiker og hjerneforsker Bjørn Juel er på besøk for å snakke om bevissthet. Hva er det? Går det noen klar grense mellom bevisst og ubevisst? Og hvordan forsker man på noe sånt? Bjørn har et prosjekt gående der han forsker på bevissthet ved livets slutt, så dette blir en kveld vi må innom alt fra biologi til etikk, fra teknologi til filosofi. Om jeg får vilja mi, må vi innom så mye av det som finnes under topplokket som vi bare rekker.

• Nilsen, Andre Sevenius; Juel, Bjørn Erik; Marshall, William & Storm, Johan Frederik (2019). Estimating Integrated Information: How noise, sampling, and perturbations affect Phi. Full text in Research Archive
• Murphy, Ricardo; Nilsen, Andre Sevenius; Juel, Bjørn Erik; Plesser, Hans Ekkehard; Hill, Sean & Nieus, Thierry [Show all 8 contributors for this article] (2019). A multiarea Hill-Tononi thalamocortical network model evaluated with proposed measures of consciousness. Full text in Research Archive
• Juel, Bjørn Erik; Nilsen, Andre Sevenius; Gosseries, Olivia; Sarasso, Simone; Larsson, Pål Gunnar & Boly, Malanie [Show all 9 contributors for this article] (2018). Measures of connectivity, complexity and signal diversity in EEG distinguish conscious from unconscious state during anesthesia. Full text in Research Archive
• Juel, Bjørn Erik; Nilsen, Andre Sevenius; Murphy, Ricardo & Storm, Johan Frederik (2018). Thalamocortical model for studying the effects of neuromodulation on network properties. Full text in Research Archive
• Juel, Bjørn Erik; Romundstad, Luis Georg; Kolstad, Frode; Storm, Johan Frederik & Larsson, Pål Gunnar (2018). Changes in EEG captured by Directed Transfer Function is sufficient to accurately classify the state of wakefulness in patients undergoing sevoflurane anesthesia in accordance with the clinician’s judgement. Full text in Research Archive
• Halder, Sebastian; Raghavan, L Venkat; Juel, Bjørn Erik; Nilsen, Andre Sevenius & Storm, Johan Frederik (2018). Effects of intracarotid sodium amobarbital procedure (ISAP) on cortical complexity. Full text in Research Archive
• Murphy, Ricardo; Nilsen, Andre Sevenius; Juel, Bjørn Erik; Plesser, Hans Ekkehard; Hill, Sean & Nieus, Thierry [Show all 8 contributors for this article] (2018). Implementation of the Hill-Tononi thalamocortical network model in the neural simulator NEST. Full text in Research Archive
• Nilsen, Andre Sevenius; Juel, Bjørn Erik; Marshall, William & Storm, Johan Frederik (2018). Calculating conscious capacity: approximations, analogues, and correlates of PHI. Full text in Research Archive
• Nilsen, Andre Sevenius; Juel, Bjørn Erik & Storm, Johan Frederik (2018). Attentional Modulation on Measures of Conscious States. Full text in Research Archive
• Juel, Bjørn Erik; Nilsen, Andre Sevenius; Farnes, Nadine & Storm, Johan Frederik (2017). Comparing electrophysiological markers of consciousness between physiologically distinct states of wakefulness. Full text in Research Archive
• Nilsen, Andre Sevenius; Juel, Bjørn Erik; Storm, Johan Frederik; Romundstad, Luis Georg & Larsson, Pål Gunnar (2017). Markers of consciousness before, during, and after anesthesia. Full text in Research Archive
• Juel, Bjørn Erik; Kusztor, Aniko; Nilsen, Andre Sevenius; Farnes, Nadine; Larsson, Pål Gunnar & Romundstad, Luis Georg [Show all 7 contributors for this article] (2017). Changes in electrophysiological markers of consciousness in response to various anesthetics. Full text in Research Archive
• Nilsen, Andre Sevenius; Juel, Bjørn Erik; Storm, Johan Frederik; Murphy, Ricardo; Plesser, Hans Ekkehard & Hill, Sean [Show all 8 contributors for this article] (2017). Implementation of the Hill-Tononi thalamocortical network model in the neural simulator NEST. Full text in Research Archive
• Nilsen, Andre Sevenius; Storm, Johan Frederik & Juel, Bjørn Erik (2017). Attentional Modulation on Measures of Conscious States. Full text in Research Archive
• Nilsen, Andre Sevenius; Juel, Bjørn Erik & Storm, Johan Frederik (2017). Proxies for integrated information of microscale networks Is it possible to predict PHI? Full text in Research Archive
• Bremnes, Thomas Rene; Juel, Bjørn Erik; Sarasso, Simone; Boly, Melanie; Casarotto, Silvia & Casali, Adenauer G. [Show all 12 contributors for this article] (2017). Unresponsive states with and without report of conscious experience show distinct patterns of EEG-based effective brain connectivity in humans. Full text in Research Archive
• Nilsen, Andre Sevenius; Arena, Alessandro; Juel, Bjørn Erik; Storm, Johan Frederik; Murphy, Ricardo & Hu, Hua [Show all 7 contributors for this article] (2017). Forsknigstorget: Hvordan kan hjernen skape bevissthet. Full text in Research Archive
• Juel, Bjørn Erik; Bremnes, Thomas Rene; Larsson, Pål Gunnar & Storm, Johan Frederik (2017). Classifying states of (un)consciousness based on one second of raw EEG. Full text in Research Archive
• Farnes, Nadine; Juel, Bjørn Erik; Nilsen, Andre Sevenius; Romundstad, Luis Georg; Larsson, Pål Gunnar & Engstrøm, Morten [Show all 7 contributors for this article] (2017). Integrated information in sub-anaesthetic ketamine measured by TMS and EEG. Full text in Research Archive
• Murphy, Ricardo; Nilsen, Andre Sevenius; Juel, Bjørn Erik; Plesser, Hans Ekkehard; Hill, Sean & Nieus, Thierry [Show all 8 contributors for this article] (2017). Implementation of the Hill-Tononi thalamocortical network model in the neural simulator NEST. Full text in Research Archive
• Nilsen, Andre Sevenius; Murphy, Ricardo; Juel, Bjørn Erik; Plesser, Hans Ekkehard; Hill, Sean & Nieus, Thierry [Show all 8 contributors for this article] (2017). Simulating deep sleep and awake states in a mammalian thalamocortical model. Full text in Research Archive
• Juel, Bjørn Erik; Romundstad, Luis Georg; Kolstad, Frode; Storm, Johan Frederik & Larsson, Pål Gunnar (2016). Differences in effective connectivity can be used to separate conscious from unconscious states in patients undergoing general anesthesia. Full text in Research Archive
• Juel, Bjørn Erik; Bremnes, Thomas Rene; Larsson, Pål Gunnar & Storm, Johan Frederik (2016). Comparing Potential Objective Measures of Human Consciousness: the Perturbational Complexity Index and the Directed Transfer Function. Full text in Research Archive
• Juel, Bjørn Erik; Romundstad, Luis Georg; Kolstad, Frode; Storm, Johan Frederik & Larsson, Pål Gunnar (2015). Monitoring Brain Connectivity to Predict Patients’ Level of Awareness. Full text in Research Archive
• Juel, Bjørn Erik; Romundstad, Luis Georg; Kolstad, Frode; Storm, Johan Frederik & Larsson, Pål Gunnar (2015). Can We Monitor Consciousness in Real Time with EEG? Full text in Research Archive

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