A repeated awakening study exploring the capacity of complexity measures to capture dreaming during propofol sedation
Imad J. Bajwa, André Sevenius Nilsen, René Skukies, Arnfinn Aamodt, Gernot Ernst, Johan F. Storm, Bjørn Erik Juel
Scientific Reports September 24, 2025 DOI: 10.1038/s41598-025-12695-z (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Experimental study Peer reviewed |
|---|---|
| Sample size | 20 |
| Population | Healthy participants |
| Intervention | propofol sedation |
| Topics | Dreaming |
| Keywords | Electroencephalography Sedation Propofol Level of consciousness Persistent vegetative state Anesthesia Burst suppression Altered state |
| Citations | 3 |
| Key findings | EEG complexity measures decreased from awake to sedated states but did not differ between periods with and without reported dream experiences during propofol sedation. |
Abstract
Abstract 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 (PCI st ) 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.