Propofol anesthesia creates a brain state where some features resemble sleep while others are more similar to coma, and embracing its full spatiotemporal complexity could improve titration of sedation, thus minimizing excessive suppression and the risk of postoperative cognitive deficits.
Key Findings
Results
Propofol anesthesia exhibits spatiotemporal patterns resembling both coma and sleep, rather than being uniquely similar to either state.
Whole-head EEG was used to analyze brain activity across three groups: individuals under propofol anesthesia, individuals during sleep, and individuals with disorders of consciousness (DoC) in the intensive care unit.
Spectral parameterization and similarity analyses were used to compare brain states across conditions.
The anesthetic brain state was found to share features with both sleep and coma rather than mapping cleanly onto either one.
The authors conclude that propofol anesthesia is neither simply 'like sleep' nor 'like coma' but a hybrid state with distinct spatiotemporal characteristics.
Results
Spectral orthogonalization identified unique neural signatures of propofol anesthesia not shared with sleep or coma.
A spectral orthogonalization approach was introduced specifically to isolate signatures unique to propofol anesthesia after removing variance shared with sleep and DoC.
Unique signatures of propofol anesthesia include posterior slow waves and frontocentral delta activity.
Reduced aperiodic activity was also identified as a distinctive feature of the propofol anesthetic state.
Frontal alpha oscillations were confirmed as a key feature of propofol anesthesia detectable via intraoperative EEG.
Results
Reduction in aperiodic neural activity under propofol anesthesia partially overlaps with REM sleep.
Aperiodic activity, which reflects the broadband non-oscillatory component of the EEG signal, was reduced under propofol anesthesia.
This reduction in aperiodic activity was found to partially overlap with patterns observed during REM sleep.
The authors suggest this reduction 'may reflect decreased cortical excitability, contributing to reduced arousal, muscle atonia, and immobility common to both states.'
This finding is notable because delta activity (< 4 Hz), another electrophysiological marker, is absent during REM sleep but present in slow wave sleep, coma, and propofol anesthesia, making aperiodic activity a point of convergence between anesthesia and REM sleep specifically.
Background
Delta activity is present in slow wave sleep, disorders of consciousness including coma, and propofol anesthesia, but absent during REM sleep.
Electrophysiological markers such as delta activity (< 4 Hz) were examined across all states.
Delta activity was identified as a shared feature of slow wave sleep, DoC (including coma), and propofol anesthesia.
The absence of delta activity during REM sleep distinguishes REM from the other states examined.
This pattern informed the framework for comparing these states and motivated the search for additional distinguishing features.
Discussion
The clinical implications of the findings suggest that recognizing the full complexity of propofol anesthesia could reduce the risk of postoperative cognitive deficits.
The authors argue that current reliance on alpha and delta activity alone does not 'fully define the brain state' under propofol anesthesia.
Embracing the 'full spatiotemporal complexity' of the anesthetic brain state 'could improve titration of sedation.'
Improved titration could minimize 'excessive suppression and the risk of postoperative cognitive deficits.'
The study's framework, using spectral parameterization and similarity analysis across sleep, anesthesia, and DoC, provides a potential basis for developing richer intraoperative EEG monitoring approaches.
What This Means
This research suggests that the brain state produced by the common anesthetic drug propofol is more complex than previously appreciated. Scientists often say that general anesthesia is 'like sleep,' but this study found that the brain during propofol anesthesia actually shares features with both sleep and coma simultaneously, rather than closely resembling either one on its own. Using detailed brain wave recordings (EEG) from patients under anesthesia, sleeping volunteers, and comatose patients in the ICU, the researchers applied advanced analysis techniques to map out what makes each brain state unique and what they share.
The study identified several brain activity patterns that are unique to propofol anesthesia — including specific slow wave activity at the back of the head, delta wave activity at the front and center, and a reduction in background brain signal that is also seen during REM (dreaming) sleep. This last finding is particularly interesting because REM sleep and propofol anesthesia are otherwise quite different, yet both show this reduction in baseline brain activity, which the researchers think may relate to reduced muscle tone and immobility seen in both states.
This research suggests that the way anesthesiologists currently monitor brain activity during surgery — primarily by looking for specific wave patterns like frontal alpha waves — may not capture the full picture of what the brain is doing under anesthesia. A more complete understanding of the anesthetic brain state could help doctors more precisely control the depth of anesthesia, potentially avoiding over-sedation, which has been linked to memory and thinking problems after surgery (postoperative cognitive deficits).
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Helfrich J, Szaflarski J, Nævra M, Romunstad L, Walker M, Mander B, et al.. (2026). Spectral mapping reveals a resemblance of the anesthetic brain state to both sleep and coma.. Proceedings of the National Academy of Sciences of the United States of America. https://doi.org/10.1073/pnas.2514098123