Many people tend to think of anesthesia as a state of “deep sleep.” When an anesthesiologist steps into the operating room, their objective is to ensure the patient remains completely unaware until they awaken—sometimes hours later. The effects of anesthetic drugs on the brain during surgery have been a topic of considerable discussion among scientists and medical professionals.
A recent study from the Yale School of Medicine—published in the Proceedings of the National Academy of Sciences on May 11, 2026—offers new insights that could reshape our understanding of anesthesia. The research titled “Spectral mapping reveals a resemblance of the anesthetic brain state to both sleep and coma,” suggests that anesthesia may involve states more similar to a coma than previously thought.
The anesthetized brain
Dr. Janna Helfrich, an assistant professor of anesthesiology and the lead author, investigated how anesthesia and pain management can be restructured to minimize long-term cognitive and behavioral effects following surgeries. Although the brain plays a critical role in ensuring patient safety and comfort during procedures, it typically isn’t monitored while under anesthesia. Most surgeries are performed without brain monitoring because, historically, tracking brain activity has been challenging.
“It’s surprising, really. Anesthesia has been around for over 150 years, but we’ve only started paying attention to the brain recently,” Helfrich noted when asked about her research’s inspiration. “Previously, we focused on vital stats like blood pressure and heart rate, but measuring brain activity isn’t yet standard practice, which is odd considering that’s where all the drugs take effect, be it anesthetics or painkillers.”
Comparing brain waves
The research team analyzed brain wave data from patients sedated with propofol, a widely used anesthetic in surgeries, employing electroencephalography (EEG) with electrodes placed on the scalp to capture brain activity. They then compared these patterns to those from patients in various states, including deep sleep and coma, as well as those fully awake.
“Instead of just focusing on the front of the head, which is standard practice, we used a full head EEG with 20 electrodes,” Helfrich explained. “This provided insights from all areas of the brain.”
The study’s results challenge the notion that anesthesia is merely deep sleep. Instead, the data reveal that the anesthetized brain can exhibit various states, some resembling sleep and others akin to a coma. Anesthesia produces unique brain activity patterns that differ significantly from other states of consciousness.
Helfrich and her team are keen on exploring the intricacies of anesthesia and its impact on the brain during surgery.
“The notion that it’s either sleep or coma is misleading. Anesthesia can embody elements of both at once, depending on the specific context,” Helfrich pointed out. “Yet, there’s also something distinctly unique about anesthesia itself.”
Enhancing anesthesia care
Patients may face difficulties post-surgery due to anesthesia, especially older individuals or those with existing medical issues, often leading to cognitive impairments or memory loss. This study emphasizes the importance of administering anesthesia in a way that avoids inducing a coma-like state, aiming to bring patients to a state akin to natural sleep.
Looking forward, Helfrich and her colleagues hope their findings will improve monitoring practices for the brain, enhancing overall health during anesthesia. Future studies may guide clinicians to steer the anesthetic experience toward a more restorative sleep-like state instead of a coma-like one.
“Sleep offers numerous benefits,” Helfrich remarked. “It rejuvenates cognitive functions, boosts the immune system, and aids metabolism. So I envision adjustments in anesthesia that encourage a sleep-oriented state, potentially alleviating some adverse effects.”
Prioritizing patient health before, during, and after surgery remains paramount for all medical professionals. By keeping track of brain activity, anesthesiologists can better tailor their care and harness sleep-related advantages during surgery.
In addition to Helfrich, the study included contributions from Randolph F. Helfrich, Jerzy Szaflarski, Marianne C. J. N Nævra, Luis Romunstad, Matthew P. Walker, Bryce A. Mander, Robert T. Knight, and Pål G. Larsson.
Lucy Nemchek serves as a communications officer at Yale School of Medicine. This collaboration is with Yale School of Medicine. Fundings for this research were provided by the German Research Foundation, the Medical Faculty of the University of Tübingen, and the Jung Foundation for Research and Science.
