A repeated awakening study exploring the capacity of complexity measures to capture dreaming during propofol sedation

Patients undergoing general anaesthesia 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 anaesthetics. 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, 24 produced reports of having had an experience, while there were 5 reports of no experience. 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 the study confirms earlier findings that EEG complexity measures significantly decrease from the awake state to the sedated state, no evidence was found that these measures differ between periods associated with dreaming and non-dreaming within the sedated state.

Contributions: Data collection, design, analysis, conception, implementation, writing.

Recommended citation: Bajwa, I. J., Nilsen, A. S., ..., Storm, J. F., & Juel, B. E. (2025). A repeated awakening study exploring the capacity of complexity measures to capture dreaming during propofol sedation. Scientific Reports, 15(1).
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