Proc Natl Acad Sci
Propofol creates brain state distinct from sleep, coma
Clinical Takeaway: Whole-head EEG may offer a more precise way to track depth of anesthesia than current forehead monitoring. Aiming for a sleep-like profile rather than deeper, coma-like suppression could help limit postoperative cognitive deficits.
Anesthesia is routinely described to patients as sleep, but its underlying neural activity has been thought to sit closer to a medically induced coma. Propofol is the dominant induction agent for general anesthesia in the U.S., used in the large majority of adult surgical cases. This study mapped where on that spectrum propofol actually falls, and whether anesthesia carries unique features of its own.
Spectral analysis showed that propofol anesthesia shared features with both sleep and disorders of consciousness, but the overlapping signatures appeared in different brain regions and at different EEG frequencies for each state. Anesthesia was not simply a deeper version of sleep or a milder version of coma.
The investigators also identified several signatures that appear specific to propofol: posterior slow waves, frontocentral delta activity, and reduced aperiodic activity. The drop in aperiodic activity partially overlapped with REM sleep and may reflect lower cortical excitability, which may contribute to the reduced arousal, muscle atonia, and immobility seen in both states.
Researchers recorded whole-head scalp EEG in 28 patients under propofol anesthesia and compared the data with recordings from 14 awake individuals, 20 sleeping individuals, and 40 patients with disorders of consciousness, including coma, in the intensive care unit. They applied spectral parameterization and a new orthogonalization approach to separate features shared with sleep or coma from those unique to anesthesia.
The findings suggest anesthesia is its own brain state rather than a substitute for sleep or a controlled coma, with quantifiable similarities to each. That distinction matters because intraoperative monitoring still relies largely on limited frontal EEG, and clinicians have had few tools to detect excessive cortical suppression. Mapping the full spatiotemporal pattern could help guide titration and may eventually allow anesthesia to be steered toward a more sleep-like profile, which the authors link to better cognitive recovery.
The study compares brain states and does not show that targeting a sleep-like pattern improves postoperative outcomes; that will require prospective testing with cognitive endpoints. The dataset is also modest in size.
"Embracing its full spatiotemporal complexity could improve titration of sedation, thus minimizing excessive suppression and the risk of postoperative cognitive deficits," the authors conclude.
Source: Helfrich JD. Proc Natl Acad Sci. 2026 May 11. Spectral mapping reveals a resemblance of the anesthetic brain state to both sleep and coma