Electrophysiological correlates of conscious experiences during sleep: Lucid dreams, sleep paralysis, out-of-body experiences, and false awakenings

Background:

Reports of vivid, emotionally intense, immersive dreams, accompanied by a sense of awareness, suggest that conscious experience can occur during sleep, challenging long-standing views that consciousness is exclusive to wakefulness [1,2].

Altered states of consciousness emerge during sleep – there are: lucid dreams (LDs), where the dreamer becomes consciously aware that they are dreaming [3]; out-of-body experiences (OBEs), characterized by a sensation of detachment from the physical body when asleep, often observing it from an external perspective [4]; sleep paralysis (SP), marked by transient atonia and hallucinations during Rapid Eye Movement (REM) sleep transitions [5]; and false awakenings (FAs), in which the sleeper dreams they have woken up, but they were still asleep [6].

Most studies examining sleep-conscious experiences rely primarily on subjective data, such as self-reports and questionnaires, and there is a critical lack of objective validation through polysomnography or neuroimaging techniques [7]. LDs have been the most extensively studied using objective methods [8,9] while other sleep-conscious experiences remain poorly characterized.

In this preprint, Herrero and team attempt to bridge this gap by investigating whether out-of-body experiences (OBEs) and false awakenings (FAs) can be distinguished electrophysiologically from standard sleep stages. The authors recorded overnight polysomnography (PSG) in seven participants who frequently experience conscious states during sleep. To objectively capture moments of awareness, participants were trained to signal the realization that they were dreaming using a well-established eye movement sequence commonly employed in lucid dreaming research. Using these signals, the researchers compared neural activity associated with different conscious sleep experiences to canonical sleep and wake states. REM sleep—classically associated with vivid dreaming and conscious mentation—and Stage 1 (S1), a transitional stage characterized by reduced awareness, served as key reference points. By contrasting these baselines, the study aimed to determine whether phenomena such as sleep paralysis (SP), out-of-body experiences (OBEs), and false awakenings (FAs) reflect variations of known sleep states or instead constitute distinct states of consciousness. The results reveal that these experiences share common features while also exhibiting neural signatures that differentiate them from both REM sleep and wakefulness.

Key findings:

Lucid dreams share features with REM sleep

LDs shared many spectral characteristics with REM sleep, particularly during phasic REM. While signs of increased cortical activation were observed, this study did not find significant spectral differences between LDs and REM. This finding contrasts with previous literature reporting elevated fast-frequency activity during LDs.

Sleep paralysis reflects a state of conscious clarity despite persistent muscle atonia

Sleep paralysis showed reduced theta power, consistent with previous findings, alongside novel increases in beta and low-gamma activity compared to REM sleep and Stage 1 sleep. These results suggest heightened cortical activation and support the interpretation of SP as a distinct conscious state—one of “lucid paralysis”—characterized by self-awareness and cognitive clarity despite persistent muscle atonia.

Out-of-body experiences constitute an internally immersive state with reduced sensory processing

This study provides the first electroencephalographic recordings of out-of-body experiences occurring during sleep and reveals neural signatures distinct from REM sleep, Stage 1 sleep, and wakefulness. The two observed OBEs were characterized by increased delta and theta power and reduced alpha, beta, and low-gamma activity relative to REM sleep and wakefulness, with particularly robust effects in OBE1. These findings suggest reduced sensory integration and processing; they support the interpretation that OBEs are internally immersive conscious states.

Out-of-body experiences and false awakenings preserve lucidity through voluntary eye signalling

Using eye movement markers, the study offers the first neurophysiological evidence of preserved lucidity during out-of-body experiences and false awakenings. A voluntary left–right–left–right eye movement signal was detected during one out-of-body experience and one false awakening, demonstrating sustained conscious awareness during these episodes. These results support the use of ocular signals as reliable indicators of lucidity in immersive, dreamlike conscious states.

Why we highlight this preprint:

This preprint reunites our three main research interests. While sleep and consciousness remain historically understudied, particularly through objective methods, both subjects are gaining interest from the scientific community, and their convergence in Herrero et al.’s study is timely and innovative. Consciousness remains one of neuroscience’s most elusive frontiers, although many aspects of sleep physiology are poorly understood. In contrast, electrophysiology is a well-established methodology, and its use in this study lends robustness to the investigation of underexplored consciousness states in sleep.

What stood out to us most was this study’s methodological originality and the novel findings reported. It complements recent literature by replicating some spectral trends, while also presenting novel insights—most notably, the authors report having captured ocular signals during SPs and are the first to use an ocular signal to mark lucidity during OBEs and FAs, as well as the first to obtain EEG recording of OBEs occurring during sleep. These contributions introduce reliable, time-locked physiological markers of subjective awareness for these conscious states.

Overall, this work contributes to a more nuanced consciousness mapping during sleep. It opens new avenues for investigating how internally generated states may emerge, stabilize, and differentiate within the sleeping brain.

Questions for the authors:

• Would you consider incorporating standardized phenomenological tools—such as ASC scales, structured dream content-coding, or validated questionnaires—to complement verbal self-reports and support classifying conscious states during sleep?
• Would it be relevant to clarify that consciousness is commonly described as involving two dimensions—wakefulness and awareness—and that, in the altered states examined, only the awareness component appears to be modulated, while wakefulness remains relatively preserved?
• Given that delta activity appears inconsistent or difficult to interpret across certain states, how would incorporating connectivity analyses or integrating functional measures help better differentiate conscious states during sleep?

References

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doi: https://doi.org/10.1242/prelights.43018

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