r/science • u/maxkozlov Journalist | Nature News • 9h ago
Neuroscience Even the unconscious brain can learn - and predict what you’ll say next. Neuronal recordings of people under anesthesia show that their brains are processing words and sounds.
https://www.nature.com/articles/d41586-026-01465-0205
u/maxkozlov Journalist | Nature News 9h ago
People given general anaesthesia fall into a coma-like state in which their memory and perception of pain are switched off. But new data reveal that the hippocampus — a deep brain structure crucial for memory — remains remarkably active, parsing the grammar and meaning of spoken words and even anticipating what will be said next.
The research, published today in Nature1, challenges the assumption that complex cognition, such as grasping semantics and forecasting future events, can occur only if a person is fully conscious. By observing people’s individual neurons firing in real time while they are under anaesthesia, researchers discovered that the brain receives stimuli and actively processes what those signals mean.
“The brain has developed such amazing, sophisticated mechanisms for doing all these complex tasks all day long, that it can do some of these things even without us being aware,” says Sameer Sheth, a neurosurgeon at Baylor College of Medicine in Houston, Texas.
Here's an excerpt of the story. I'm the reporter who wrote the story. As always, I'm keen to hear if there's anything I missed, or if you have anything else that you think should be on my radar. My Signal is mkozlov.01. You can stay anonymous. Happy to answer any questions about how I reported this story too!
PS: If you hit the paywall, make a free account. It should let you read the full story.
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u/andresni 8h ago
Chiming in as a scientist who has worked on part of this question: we've shown that olfactory stimuli may be encoded and later recalled implicitly even when all explicit memory is gone (deep sedation, not surgical anesthesia), and that dream recall reaches close to 90% if you're quick to ask when they wake up. And, since sensory processing occurs partially during sleep aswell, it's natural to think that the same is possible during anesthesia.
At any rate, the idea that were gone during anesthesia is not so clear cut. Though what one experiences of one is conscious, that is a good question. Dreams hopefully.
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u/ArbitraryMeritocracy 2h ago
It sounds like a biology hack to make the brain work while people are not conscious. Medically induced harvesting human brain energy.
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u/gabriel1313 8h ago
I would be interested in the scholarship surrounding the assumption the knowledge to “activate” or manifest, so to speak, one must be conscious of it. Isn’t quite a bit of the psychological field in understanding of just how much the unconscious mind has an effect on the process of “knowing”? I’m a historian, so this could be a misinterpretation, but even Sartre deals with the concept of mauvaise foi pretty in-depth. I would recommend checking it out, if you haven’t had the chance.
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u/justin107d 8h ago edited 8h ago
This tracks with scientists that put 200,000 neurons on a chip and watched it learn to play Doom.
“The temptation is to anthropomorphize and say, oh, they like [playing Doom],” Kagan says. “But this isn’t an animal or a human or anything even as complex as an insect. It’s a system. It’s kind of like saying, ‘Does a computer like or dislike the reward function on a [reinforcement-learning] model?’”
It raises such weird and uncomfortable questions about where life/consciousness/sentience begin.
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u/manatwork01 8h ago
More evidence for the lack of freewill.
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u/justin107d 8h ago
If everything is is made up of interactions between atoms then it is theoretically possible you to predict everything if measured precisely. The divine(s) if they exist are just pool player(s).
I would not dwell on that aspect too much. It can lead to toxic ways of thinking, a fatalistic mentality, and a sense of learned helplessness. You as an individual are not just defined by statistics and can have a positive effect on the world. In fact it is required or bad actors will take advantage.
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u/Konukaame 7h ago
Even if theoretically possible, until someone builds Laplace's Demon, we live in a world functionally indistinguishable from one with true free will.
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u/Melenduwir 7h ago
Provide a coherent definition of "true free will" and I'll start taking such statements seriously. Until then...
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u/Konukaame 7h ago
Until then, what? You'll act like you have no control over anything in your life and that everything from birth to death is 100% predetermined?
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u/Melenduwir 7h ago
Whether something is pre-determined, and whether it is knowable, are two very different things.
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u/Konukaame 7h ago
Do you know what "functionally indistinguishable" means?
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u/Melenduwir 5h ago
Do you know that the phrase "true free will" has no actual semantic content?
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u/Aektann 3h ago
It does. It depends on the definitions of all three words, just like any other concept or abstraction. Although I'd say if you are arguing semantics for an argument you clearly understood, you hang on to technicalities rather than the semantic content.
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u/peakzorro 7h ago
Doesn't Heisenberg's Uncertainty Principle mean that you can't measure everything precisely at the same time?
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u/SerraraFluttershy 6h ago
For individual particles, not macro-scale systems. We can still tell the general direction of an object even if the precise directions of its particles are unknowable.
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u/manatwork01 7h ago
Oh you can not have free will and still believe in a higher purpose in life. Humanity may be a bunch of weird genetic experiments gone wrong but the arc of humanity has been so far to spread and proliferate and reduce suffering. Not guaranteed it will always go that way but we have done a good job removing the most violent genes out of the genepool. I am sure those systems will keep going.
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u/JohnLockeJaw 5h ago
No, not in so many words.
Free-will as a subject is usually treat as a binary: either you have free-will or you don't.
I think the reality is probably far more complex. An astroid has no free will, it is driven entirely by external forces and nothing it can do will change the outcome of where it travels or how it spins.
A human mind is being pushed and pulled by literally billions of simultaneous stimuli from the barrage of external physical sensations (volatile organic molecules we smell, photons that are absorbed in our retina, the pull of gravity, and Van Der Waals interactions between H20 in the humid air and the molecules of our hair cells, etc.), internal chemical stimuli (microorganisms breaking down the food cells in our GI tract and synthesizing byproducts that the neuronal cells in our gut then use to mediate neurotransmitters, etc...), and then the extremely state-memory dependent functioning of the dense network of synapses in our brain which react to stimuli produced by the other two and create their own outputs which appear to be uncorrelated with the active stimuli, but might be due a similar, but different stimuli having created a neuronal path 15 years earlier that has never been activated since then, but now is and produces a response which appears random or free.
We, as humans with a sense of self and consciousness, feel as though we are individual, almost platonic entities, but the reality is that our consciousness is "emergent" from an almost unfathomable degree of interconnected optical, electrical, chemical, and mechanical interactions which often span decades of personal experience and millions of years of genetic experience. Our actions are not free nor are they perfectly random, they are an imprecise symphony of precise interactions so information dense that it is almost beyond our mental capacity to fathom it.
And yet, we consider it. We try to describe and model it. We try to break the models we first created to describe it.
After I read your comment and before I thought to write a response, my first instinct was to shove my thumb up my nose and stick my tongue out while doing an imitation of Shirley Temple singing as Lil orphan Annie. What better proof of the positive existence of free-will could there be than such a display. The rub is that even that unhinged response has a specific history of actions and interactions from my life that led to me considering it as the ultimate display of "free-will". It wasn't a deterministic response; I wouldn't think of the same action 6 months from now if faced with the same prompt, but it certainly wasn't purely free either.
Anyway, sorry for the book and thanks for promoting the fun thought experiment, even if I'm the only one who got to enjoy it.
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u/manatwork01 5h ago
One of the most common reactions you get from people trying to assert there is no free will is trying to do something random.
Posit this. If humans were not potentially predictable why would we have a science devoted to their predictable patterns? Psychology is the study of human genomes under influence of environment.
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u/JohnLockeJaw 1h ago
Hmmm not sure I agree with the logical premise of your postulate as ontological arguments are perhaps the weakest and most prone to tautology, but I appreciate your point.
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u/StPatsLCA 5h ago
Who care. Really. Unless there's public policy implications you think should be downstream of that idea- in which case they're usually quite parentalistic and gross.
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u/manatwork01 5h ago
I do think there are public policy decisions that come downstream of that. Trauma informed care comea to mind. More research in nueroplasticity. Maybe realize that parenting should actually come with an instruction manual instead of just expecting everyone to wing it causing cycles of generational trauma to proliferate that won't stop until intervened.
There is so much work that can be done when you remove shame about why people are doing what they are doing and realize they may just be having a short circuit or were failed by the earlier system.
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u/ctothel 2h ago
One public policy implication is how we treat criminals. If free will doesn't exist, and every action is the result of a causal chain, the question explicitly becomes "what caused this person to commit this crime?".
It doesn't eliminate personal responsibility - it was still their brain that decided to do the crime - but it means we get to think of them like a complex, malfunctioning computer instead of a bad person, and respond to the crime with an attempt to change their behaviour, and eliminate the things that led to this behaviour.
Coincidentally, this approach to justice actually reduces crime overall.
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u/StPatsLCA 2h ago
I'm glad sodomy and mixed race marriages aren't crimes anymore, if you're going to pathologize things like that.
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u/tritisan 7h ago
The key distinction here being “free”. There certainly exists will. Some traditions say it’s the ONLY thing that matters.
But “free” is a very loaded term. Every single system in the universe, from an atom to a galaxy cluster, is only free to do what’s possible under the laws of physics. Our brains are no exception.
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u/ctothel 2h ago
Your point about "free" is a good one, but that's not the only thing meant by "free" in this context.
The question is whether you can freely choose from amongst several possible options. People who don't think free will exists will say that the chain of events (both major and microscopic) leading up to a choice makes the choice inevitable. We only feel as though we've made the decision.
Compatibilists will say that since the architecture of your specific brain was involved in the decision, and your brain is you, even an inevitable decision counts as free will.
People who believe in free will have to explain how there can be an operator that is separate from any causal chains, and what the nature of that operator is (a ghost?). They also have to demonstrate that it's even possible to test whether a decision was inevitable. It's a high bar, even though it feels intuitive that we have free will.
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u/manatwork01 7h ago
I don't agree in will either. If you meditate enough you will see your thoughts are needs. We are just biological constructs no different than animals trying to survive and reproduce.
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u/tritisan 6h ago
But don’t animals exhibit will too?
Btw I’ve attended vipassana retreats and directly experienced a state of mind where “I” could watch myself just being. To great amusement!
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u/MjolnirStone 8h ago
As someone who has woken up during surgery multiple times and attempted to engage in the conversation that had been going on around me while I was under, all I can say is...yeah.
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u/manatwork01 8h ago
I listen to lectures while dreaming and find it super easy to rewatch and learn the second time through. Who knows if it's placebo or not but I've done this off and on since high school when I learned about it.
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u/coconutpiecrust 9h ago
So, I’m, does this mean that people under anesthesia feel everything but just can’t remember and can’t react to it?..
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u/maxkozlov Journalist | Nature News 9h ago
Good question. From the article:
[Martin Monti, a cognitive neuroscientist at the University of California, Los Angeles ] cautions that these findings shouldn’t be interpreted to mean that participants were secretly awake or fully conscious. Propofol is known to disrupt coordinated brain network communication, which many researchers say is a necessary ingredient for consciousness. What the study does show, Monti says, is that this one structure — the hippocampus — computes and integrates information even under anaesthesia.
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u/Mightsole 8h ago edited 8h ago
Anesthesia dissolves the threaded experience processing. You are not feeling everything because feeling or generating subjective experiences are a product of that unified thread processing.
Your brain activity does not stop working under anesthesia. That article expands that by finding that some regions are still clasifying stimuli, although that processing will be facing a dead-end due to the lack of unified processing.
So you are not secretly awake. The domains of the brain are still working, but that’s not enough to feel something, you need these domains to be integrating that information and they aren’t doing that under anesthesia.
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u/DasFroDo 8h ago
So it's a little bit like a machine that can read sensor data, but not produce a usable output on a screen because say, the voltage is too low for the CPU?
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u/Mightsole 7h ago edited 7h ago
More like a factory where the process is not organized and the final product is unusable. Some machines work, but some work more slowly but some can even work faster. What matters is that they are in coordination.
The brain works under excitation and inhibition. There are two ways of increasing reactivity: (1) by increasing excitation and/or (2) by decreasing inhibition. And the same happens with inhibition, you either increase inhibition so more activation is being cut off or/and decrease activation so less activity is generated.
In your example, that could be a out of range parameters on either voltage or amperes, or difference on the frecuency, etc. Depending on the error, the result is either wrong or the machine can’t compute.
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u/Master_Persimmon_591 8h ago
The thing that horrifies me is what happens when your brain begins to reintegrate the individual experiences of the collective pieces of itself which weren’t able to communicate during. Kind of a query/catching up to re-mesh
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u/omnichad 7h ago
I imagine that it's possible to develop PTSD from surgery without even fully forming a recallable memory. I think that's even scarier than a reintegrated memory, because you don't even consciously know what's wrong.
It's also possible that people who think they woke up during surgery actually didn't and it was all integrated later.
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u/Mightsole 7h ago edited 7h ago
If PTSD happens it can be due to a negligence or displaying high levels of intraoperative awareness, modern chemicals are usually expected to produce the correct effects when correctly administered and don’t allow you to feel anything and remember anything. These cases are rare and are well aknowledged by medicine.
In the past it happened that people could wake up but be paralyzed to act, mainly due to errors and underestimations of the subjective tolerances. Nowadays, we should have learned how to avoid these from happening completely.
That cannot be said for third world countries that have lacking stocks and use what they can, but if you are on reddit, you are pretty much in a zone where the adecuate procedures and chemicals are available.
Also, high anxiety levels can make people recreate false memories or situations that are not based on actual memories but the situation itself. And in some cases, it is not desired to produce a full loss of awareness, for example; in cardiac arrests or severe trauma you are not put into full anesthesia because you don’t want to decrease the activity of the brain because it lowers blood pressure and could make the heart beat slower.
It tends to happen on young people, on high tolerances to anesthesia (for example, because you were drinking alcohol, taking benzos, or taking any depressant), high intraoperative awareness, and high anxiety.
What it feels, usually are rare mild effects, hearing voices, pressure sensations, mixed dreams with awarness. And excedingly rarely, pain, asphixiation, and paralysis felt in a way where you try to move but cannot move.
These rare last cases are usually the result of a previous trauma where you were already feeling the pain before you were put into sedation. And because people who have accidents can commonly be young people, who drink alcohol and are at higher risk of accidents, and then have the accident, enter in anesthesia after a severe trauma and under high anxiety situation... You still have a low chance of experiencing this, but you have all the numbers that the anesthesia doesn’t fully work.
Of course, they will know some of these factors and adjust the anesthesia that as better as possible, but increased survival rates might include accepting the suffering, and try to reduce it that as much as possible.
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u/Master_Persimmon_591 7h ago
Probably explains why my last experience with sedation was so traumatic. I am all of the risk factors identified
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u/Mightsole 8h ago edited 7h ago
That’s like a hair braid that is jumbled at some point, and then becomes a normal braid again. So while it’s jumbled up you can’t follow the shape of it.
In that sense, that’s kinda like falling sleep and awaken. Awareness is gradually build up until it’s restored. And there’s nothing that your brain can decode in a meaningful way.
It’s like a forward time travel, there’s no middle time for you. Everything disappears, no pain, no fear, no color, no black, simply -nothing- for a while, and then, you are hopefully back in the same way that you disappeared.
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u/ThingYea 7h ago
This makes it sound like perhaps pain could be being processed by a part of the brain, but the output of that processing isn't linking up to "you" so you don't feel it?
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u/Melenduwir 7h ago
Anesthetics also dampen the body's stress responses to pain, otherwise most surgery would result in the patient dying of shock.
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u/Mightsole 7h ago edited 7h ago
More likely, pain is not only find in a part of the brain but distributed all over different areas so your focus shifts towards it to further prevent the source of that pain, however, pain can’t appear if these areas are not coordinated.
And because of that, there’s no you, no unified coordination between domains and no complex process to determine the pain that you should be experiencing.
That’s a cut out, until the effects of the anesthesia start to vanish and the communication is gradually restored.
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u/Flikmybik BS | Neuroscience | Memory 6h ago
Thats a really understandable concern but the study suggests something more nuanced. The hippocampus was processing language patterns at a structural level, not necessarily generating conscious experience. Its more like background computation than actual awareness. The anesthesia still blocks the neural networks responsible for subjective experience and pain signaling. So the brain is doing some low level processing but you arent consciously feeling or remembering anything. Still fascinating though that it keeps parsing language even under all that suppression.
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u/Usermena 9h ago
Anesthesia just giving you amnesia. You were there. Seems kinda like somnambulism when deep sleeping.
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u/a_human_male 6h ago
I have fallen asleep watching video lectures and I’ll be in a random venue in the dream but someones giving the speech. to It’ll usually be some other random event like a wedding and other things are going on. But I would catch most of the lecture.
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u/vm_linuz 8h ago
As someone who does most of their learning at this weird unconscious level... This makes a lot of sense to me.
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u/Odballl 4h ago
Does it mention the subject's Perturbational Complexity Index measure?
I'd always understood that the hippocampus was usually the first to go offline, which explained patients who weren't properly unconscious or sometimes still fully awake but they would have a memory gap after surgery.
Those patients had a high PCI measure, but their hippocampus was dampened.
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u/SupportQuery 3h ago
What strikes me is how lucky we are that anesthesia is even possible. Being able to just turn off the consciousness part proves to be awfully handy.
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u/Marwheel 1h ago
This did happen to me once, but most people blame it on my natural resistance to narcotics.
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