--- description: Brain monitoring is uncovering surprising similarities among different anesthesia drugs. title: What Anesthesia Does to the Brain, According to a New Study image: https://static.time.com/v3/assets/bltea6093859af6183b/blt4eb9e8e4e1c0d452/6988604c8e06017e23461fdb/brain-health-illo.jpg?branch=production&width=2400&quality=75&auto=webp&crop=16:9 ---  * [Health](/section/health/) ## Health Update your preferences in [Account Settings](/account/preferences/) Close * [Brain](/tag/brain/) ## Brain Update your preferences in [Account Settings](/account/preferences/) Close # What Anesthesia Does to the Brain, According to a New Study by [Veronique Greenwood](/author/veronique-greenwood/) ## Veronique Greenwood Update your preferences in [Account Settings](/account/preferences/) Close Mar 23, 2026 4:25 PM CUT  Illustration by Sydney Rae Hass for TIME by [Veronique Greenwood](/author/veronique-greenwood/) ## Veronique Greenwood Update your preferences in [Account Settings](/account/preferences/) Close Mar 23, 2026 4:25 PM CUT There’s something a little bit magical about anesthesia. One minute you’re there, the next you’re not—and as you go under, you might entertain the nurses with [some bizarre chit-chat](https://www.buzzfeed.com/lizmrichardson/patient-anesthesia-surgery-stories "undefined") you’ll be embarrassed to hear about later. Anesthesiologists use a variety of drugs, both injected and inhaled, to create this effect. But while [careful monitoring of the patient’s vital signs](https://time.com/archive/6731734/whats-up-doc-3/ "undefined") helps make anesthesia very safe, much is still unknown about how, precisely, these drugs have their effects. A [new paper](https://www.cell.com/cell-reports/fulltext/S2211-1247%2826%2900126-9 "undefined") published in _Cell Reports_, in which researchers work with primates, sheds some light on the question. Researchers found that three very different anesthetics all destabilize macaques’ [brain activity](https://time.com/5700721/neural-activity-longevity-study/ "undefined") the same way, despite acting on completely separate brain molecules. This supports the idea that anesthesia’s effects might be down to something broader than the individual pathways drugs interfere with, like interrupted communication between groups of neurons. Understanding how drugs have their effects might one day help doctors calibrate doses even more precisely, and perhaps help illuminate what it means to be conscious. ## What anesthesia does to the brain Propofol, [ketamine](https://time.com/collections/davos-2020-mental-health/4876098/new-hope-for-depression/ "undefined"), and dexmedetomidine are all commonly used anesthetics, but they act on different systems in the brain, says Earl Miller, a professor of cognitive neuroscience at MIT and an author of the new paper. How they manage to have similar effects on consciousness, then, is an interesting question. “What we've been finding over a number of studies over the past 10 years is it doesn't just simply shut off your cortex,” the portion of the brain responsible for higher-level processing, says Miller. “It changes the dynamics of the cortex, and this paper is another way of looking at that.” When you’re awake, messages between neurons fly around your brain, producing patterns of electrical activity familiar to doctors and scientists, who can observe them on an electroencephalogram (EEG) from electrodes placed around the scalp. These are the dynamics Miller is referring to, and when someone falls asleep or goes under anesthesia, the [patterns shift dramatically](https://hms.harvard.edu/news-events/publications-archive/brain/anesthesia-brain "undefined"). In the new paper, the researchers studied the effects of these three drugs on rhesus macaques. Instead of fitting the macaques with scalp electrodes, the researchers surgically placed electrodes directly in the brain, enabling close monitoring of the kinds of activity picked up by EEG. ## How the brain reacts The researchers watched the macaques’ readings as they received the anesthetic drugs, and observed the familiar patterns of unconsciousness taking over. Then, curious to see how the brain would respond to changes in the environment, they played sounds. In the conscious state, says Miller, such perturbations only briefly affect how the brain behaves. But the brains of the anesthetized macaques showed much less stability. “You knock it with a perturbation, and it takes longer to recover and get back on track again,” he says. One way to think about it is that the conscious brain is like a top that’s spinning quickly, able to recover from bumps and jolts. The unconscious brain is like a top that’s spinning more slowly and is more vulnerable to disruptions—wobbly, in a way. The researchers observed this instability regardless of the drug, which is “really striking,” says Ben Palanca, a professor of anesthesiology at Washington University School of Medicine who was not involved in the study: “They find something quite similar across the three anesthetics that have very different primary mechanisms.” It raises questions about just what that instability reflects, on the level of neurons and how they talk to one another. ## Monitoring the brain during surgery Understanding how the brain operates under anesthesia is more than a matter of curiosity. It’s the kind of information that might eventually influence how anesthesia is monitored and administered. Though EEG is used in some surgeries to keep track of patients’ responses to anesthesia, in the U.S. it “is not standard,” says Palanca. Emery Brown, a professor of anesthesia at Harvard Medical School who is an author of the new study, has been [a vocal advocate of the practice](https://picower.mit.edu/innovations-inventions/eeg-monitoring-anesthesia "undefined"), arguing that keeping an eye on brain activity could mean giving smaller doses of drugs, with fewer side effects. Indeed, EEG can provide a powerful way to monitor patients’ level of unconsciousness, and in Europe it is more widely used during surgery, says Darren Hight, a research scientist at the University Hospital of Bern in Switzerland, who was not involved in the new paper. “We're experiencing a bit of a revival in EEG at the moment,” he says. “A lot of people are interested. A lot of people are starting to learn about it.” Understanding brain activity under anesthesia could help doctors personalize medicine dosing. “If we can deliver more precise doses of anesthesia by monitoring these signatures in the brain, we can reduce the amount of anesthesia, and reduce the risk,” says Miller. And work like that in this new study might even lead to insights into what consciousness looks like. “If you look across different anesthetics, and you find a universal signature of unconsciousness,” Miller continues. “It gives you a big point in the correct direction of what's required for consciousness.” ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/article/2026/03/23/anesthesia-drugs-surgery-affect-brain/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/article/2026/03/23/anesthesia-drugs-surgery-affect-brain/"},"headline":"What Anesthesia Does to the Brain, According to a New Study","datePublished":"2026-03-23T16:25:14.013Z","dateModified":"2026-05-13T06:52:26.154Z","description":"Brain monitoring is uncovering surprising similarities among different anesthesia drugs.","url":"https://time.com/article/2026/03/23/anesthesia-drugs-surgery-affect-brain/","keywords":["Brain"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/blt4eb9e8e4e1c0d452/6988604c8e06017e23461fdb/brain-health-illo.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Veronique Greenwood","jobTitle":"","url":"https://time.com/author/veronique-greenwood/"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/blt4eb9e8e4e1c0d452/6988604c8e06017e23461fdb/brain-health-illo.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"TIME.com stock health brain","caption":"TIME.com stock health brain","creditText":"","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/brain/","name":"Brain"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/article/2026/03/23/anesthesia-drugs-surgery-affect-brain/","name":"What Anesthesia Does to the Brain, According to a New Study"}}]}] ```