EEG Lempel-Ziv complexity varies with sleep stage, but does not seem to track dream experience.
Arnfinn Aamodt, André Sevenius Nilsen, Rune Markhus, Anikó Kusztor, Fatemeh Hasanzadehmoghadam, Nils Kauppi, Benjamin Thürer, Johan Frederik Storm, Bjørn Erik Juel
Frontiers in Human Neuroscience 2022 DOI: 10.3389/fnhum.2022.987714 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Observational cohort Peer reviewed |
|---|---|
| Population | Participants in evening sleep experiments after partial sleep deprivation |
| Intervention | partial sleep deprivation |
| Topics | Dreaming |
| Keywords | EEG Complexity Consciousness Sleep |
| Citations | 29 |
| Key findings | Within NREM2 sleep, EEG LZC did not differ between dream and non-dream awakenings and did not correlate with subjective dream ratings, failing to replicate a previous finding. |
Abstract
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.
Comparable studies
Other observational and cohort studies on dreaming, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Lucid Dreaming: a State of Consciousness with Features of Both Waking and Non-Lucid Dreaming Student volunteers trained to become lucid and signal lucidity with horizontal eye... | 2009 | Observational study | n = 6 |
| Nightmare Prevalence, Nightmare Distress, and Self-Reported Psychological Disturbance Young adults with a mean age of 20 years | 2002 | Prospective observational study | n = 116 |
| Long-term effects of extreme situational stress on sleep and dreaming Survivors of traumatic events who complained of sleep disturbances, compared with... | 1987 | Case-control study | n = 11 |
| The relationship of nightmare frequency and nightmare distress to well‐being Adults who reported dreams | 2004 | Observational cohort | n = 147 |
| Dreaming in NREM Sleep: A High-Density EEG Study of Slow Waves and Spindles Healthy human subjects | 2018 | Observational cohort | n = 14 |
Citations in the library
Cited by 10
- Breathwork-induced psychedelic experiences modulate neural dynamics. Cerebral Cortex August 1, 2024
- DREAM: A Dream EEG and Mentation database May 16, 2023
- Psychedelics and disorders of consciousness: the current landscape and the path forward. Neuroscience of Consciousness June 15, 2024
- Sensory modality defines the relation between EEG Lempel–Ziv diversity and meaningfulness of a stimulus Scientific Reports March 1, 2023
- Subanesthetic ketamine alters EEG signal complexity: Implications for treatment stratification in depression. Journal of Affective Disorders October 1, 2025
and 5 more in the library
Cites 33
- An information integration theory of consciousness BMC Neuroscience November 2, 2004
- Neural correlates of consciousness: progress and problems Nature Reviews Neuroscience April 20, 2016
- A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior Science Translational Medicine August 14, 2013
- The entropic brain: a theory of conscious states informed by neuroimaging research with psychedelic drugs Frontiers in Human Neuroscience 2014
- Are the Neural Correlates of Consciousness in the Front or in the Back of the Cerebral Cortex? Clinical and Neuroimaging Evidence Journal of Neuroscience October 4, 2017
and 28 more in the library