EEG Lempel-Ziv complexity varies with sleep stage, but does not seem to track dream experience
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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.
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Studies capturing both N2 and N3 experiential reports often report slightly higher null report rates in N3 than N2.
“For example, studies capturing both N2 and N3 experiential reports often report slightly higher null report rates in N3 than N2.43–45,65”
From We are the Sensors of Consciousness! A Review and Analysis on How Awakenings During Sleep Influence Dream Recall (2025) · cites this paper as [43]
Section 2.2 (Participants and data; page unavailable) reports awakening reports from both NREM2 and NREM3, and Figure 1C’s caption says reports were classified by sleep stage as no experience or dream experience. The text gives the NREM2 no-experience count but not the NREM3 count or a comparison of null-report rates, so it does not establish that NREM3’s rate was slightly higher. (LLM, conf=0.78)
Experimental — accuracy not yet measuredTwo studies attempting to correlate the diversity of dreams with EEG signal complexity resulted in null or conflicting findings.
“This uncertainty is further emphasized by two studies attempting to correlate the diversity of dreams with EEG signal complexity, resulting in null or conflicting findings.42,43”
From We are the Sensors of Consciousness! A Review and Analysis on How Awakenings During Sleep Influence Dream Recall (2025) · cites this paper as [43]
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Cited by
Sorted by citations
Stucky, B. (2025) · Nature and Science of Sleep · doi:10.2147/nss.s506461 · Cited by 7 · see citing works
- Authors
- Aamodt, A., Sevenius Nilsen, A., Markhus, R., Kusztor, A., HasanzadehMoghadam, F., Kauppi, N., Thürer, B., Storm, J. F., & Juel, B. E.
- Affiliations
- University of Oslo (NO)
- Oslo University Hospital (NO)
- Corresponding author
- Aamodt, Arnfinn
- Juel, Bjørn Erik
- Venue
- Frontiers in Human Neuroscience
- Publisher
- Frontiers Media SA
- Published
- 2023-01-10
- Volume
- 16
- Pages
- 987714-987714
- ISSN
- 1662-5161 (ISSN-L)
- PMC
- PMC9871639
- OpenAlex
- W4315471554
- Cited by
- 30
- References
- 20
- Citations by year
- 2026: 9 · 2025: 9 · 2024: 7 · 2023: 4 · 2022: 1
- FWCI
- 4.34
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- Frontiers in Human Neuroscience (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- NORA - Norwegian Open Research Archives (submittedVersion, cc-by)
- Funders
- Norges Forskningsråd
- Horizon 2020 Framework Programme
- Topics
- Life Sciences › Neuroscience › Cognitive Neuroscience › Sleep and Wakefulness Research
- Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and related disorders
- Social Sciences › Psychology › Experimental and Cognitive Psychology › Philosophy and Theoretical Science
- Keywords
- Lempel-Ziv complexity, EEG complexity, sleep stages, NREM sleep, dream experience, dream vividness, posterior cortex, sleep deprivation, reproducibility, subjective experience
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