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• 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.

• 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.

• 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.

• 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.

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