How Does Anesthesia Work? (Spoiler Alert: We Still Don’t Really Know)

I find all aspects of anesthesia endlessly interesting (as evidenced by this Substack!). But probably the most interesting part is that we still don’t really fully know how it works.

There are parts we do understand, in extraordinary detail. We can identify the receptors anesthetic drugs bind to, measure how they change individual neurons, watch the electrical rhythms of the brain reorganize, and track the breakdown and return of communication between entire brain networks.

But if you are part of the team that finally explains how all of those changes become the disappearance of conscious experience, there is a good chance you are going to win a Nobel Prize for it.

To be fair to anesthesia, science can’t explain how the consciousness you’re having right now arises either. Anesthesia didn’t create that mystery—it just gives us a switch.

It Isn’t One Thing

Part of the confusion is that we say someone is “under,” as if anesthesia were a single state made by a single drug.

It isn’t. General anesthesia handles several separate things at once: you shouldn’t be consciously aware of the operation, shouldn’t feel pain, shouldn’t form memories of it, and shouldn’t move. Those effects aren’t interchangeable. A sedative can relax you without making you unconscious. An opioid treats pain without reliably making you unconscious. A paralytic stops movement while providing no unconsciousness and no amnesia at all.

Stillness is not anesthesia. Each effect is its own dial. And the memory dial is where things get really strange.

You Were Awake. You Just Don’t Remember It

Before almost every surgery, I have a conversation the patient won’t remember having. I ask about their teeth, their last meal, I might joke about their socks. They answer. Then they wake up in recovery and tell the nurse, with total sincerity, that they never even made it to the operating room.

But they did. They talked to me the whole way there.

Most people assume the forgetting is just a side effect of being unconscious. It isn’t—because for a lot of what you don’t remember, you weren’t unconscious. You were awake, following instructions, moving yourself onto the table. You just weren’t recording any of it.

The dose that stops you forming new memories is lower than the dose that puts you to sleep. So there’s a window where you’re awake by every outward sign—you’re talking, moving, responding—while the recorder is already off.

The drug behind that is often midazolam (brand name Versed), a relative of Valium we give before heading to the OR. It softens the anxiety, and it’s a remarkably reliable eraser—we choose it partly for that. It works by boosting GABA, the brain’s main “slow down” signal, which quiets neurons everywhere. But the hippocampus—the small structure that turns a passing moment into a storable memory—quiets first and most.

It’s like the recording studio goes dark while the rest of the building is still lit. The experience streams in; nobody hits record.

So when a patient says “I closed my eyes and then I was in recovery,” it isn’t that the brain lived eight hours as an instant. It’s that no continuous memory was made in between. The last memory before surgery sits right beside the first one after.

It Doesn’t Turn the Brain Off — It Reorganizes It

The transition from awake to unconscious usually comes from propofol, the milky-white medication that works faster than anyone expects. One moment they’re looking at me; the next, they’re not responding.

And here’s the surprise: the brain doesn’t go quiet. On an EEG, activity becomes slower and more synchronized, locked into big repetitive waves. The awake brain constantly moves among many different patterns—taking in information, comparing it with memory, updating its picture of the world. Under anesthesia, that range collapses. Activity becomes repetitive, local, and unable to travel across the brain.

The clue is in what still works. An unconscious brain often registers the first flicker of a sound— the hearing center responds—but the signal doesn’t spread through the rest of the network. The sound reaches the brain. What fails is the step that turns it into “someone is speaking to me”.

I picture it less like the lights going out and more like the phone lines between the rooms going down: rooms still lit, still busy, no longer talking to each other.

How Different Drugs Do the Same Thing (In Different Ways)

Here’s what researchers discovered: Three completely different anesthetic drugs, each working through different mechanisms, all did the same thing to brain cells.

Brain cells have parts that receive feedback from other parts of the brain. Think of it like a cell’s antenna—it’s how the cell stays connected to everything else. What the researchers found was that these three different drugs all blocked that antenna. The cell stayed active, but it couldn’t receive signals from the rest of the brain anymore. The feedback line went quiet.

Different drugs. Same result: disconnection.

Not every anesthetic even slows the brain down. Ketamine can actually increase activity in some regions, and the brain can look busy while the patient is completely disconnected from the world. That’s one of the biggest clues we have: unconsciousness can’t just mean “less brain activity.” Sometimes there’s more.

What fails is the brain’s ability to organize activity into a single, coherent experience—to have all the different pieces talking to each other. Different receptors, different patterns, same endpoint: a brain that can’t hold the conversation together.

But no single receptor, structure, or rhythm has been shown to explain every anesthetic in every person. That’s the part we’re still solving.

So Do We Understand Anesthesia?

Yes, and not completely. We understand the drugs extraordinarily well: how fast they act, how they clear, how illness and age change the dose, how to support your breathing and blood pressure the entire time.

What we don’t have is one clean line from a molecule to the disappearance of the self.

And here’s the reassuring part: safety doesn’t depend on solving consciousness. Anesthesia isn’t a drug you’re given and left to work on its own. It’s a changing state that’s tended the whole way through. The surgery gets more stimulating, and the anesthetic changes. Your pressure shifts, and it changes again. The person at the head of the bed is part of the system.

I can tell you exactly what propofol does to your receptors and still find the moment remarkable: you’re talking to me, and then you’re not, and hours later you come back with no memory of the time between.

My job isn’t to solve the mystery of the mind. It’s to know what the anesthetic is doing to you, respond to every change, and stay at the head of the bed until you’re safely back.

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If this gives you a different understanding of what happens when you go under, share it with someone who’s having surgery soon. Knowing that anesthesia is a carefully tended state—not just a drug and hope—makes the whole thing feel less mysterious and more secure.

The Art of Anesthesia explains what actually happens before, during, and after anesthesia — and the parts patients rarely get to see.

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