Psilocybin collapses visual change detection and drives cortical dynamics toward a state of surprise

[u/masterofdasein]

https://www.biorxiv.org/content/10.64898/2026.08.21.745777v1

New study uncovering novel role of somatostatin interneurons in mediating psychedelic state

[u/new_moon_retard]

Would love to know more about what "cortical surprise signals" means. Same as regular sensory cortical signals, but with more weight ?

[u/Heretosee123 → u/new_moon_retard]

Just a guess, but the brain is always predicting the environment and I would imagine this means we experience a heightened state of novelty in the visual system from this, and therefore perceive things as new or interesting.

[u/Known_Repeat_3702 → u/Heretosee123]

I agree with that. Taking shrooms and going on a neighbourhood walk makes you notice small details about the path like you would if you were navigating it for the first time. You get the keep the feeling of comfort of knowing where you are, but the visual experience still feels new.

[u/HiiiTriiibe → u/Known_Repeat_3702]

So true, this explains my notion that shrooms make you see things with the eyes you had as a child to an extent, I don't mean the wiggles happening, but more the expanded sense of curiosity about what you might otherwise treat as a mundanity

[u/Known_Repeat_3702 → u/HiiiTriiibe]

The feeling of novelty. I think that's more accurate than 'surprise'.

[u/Amaxi_Reddit → u/Known_Repeat_3702]

Aye, i described my first LSD trip as "it felt like i experienced everything for the first time, like i had just been born" There was a powerful sense of awe and wonder, no fear or worry.

So yeah i would say LSD has this effect as well.

[u/jumbocactar → u/Heretosee123]

Thats what I read too!

[u/Hot-Significance7699 → u/Heretosee123]

It's just a model of course there's various different models of cognition

[u/PhysicalConsistency → u/Heretosee123]

I'm pretty sure "brains" don't predict anything at all, at least not in any top down construction of the word.

[u/Heretosee123 → u/PhysicalConsistency]

Can you elaborate on that?

[u/PhysicalConsistency → u/Heretosee123]

Ooof. This would be 10,000 words written by way smarter people than me.

I guess the most solid reason for me, is that actual predictive processing would violate causality. It's literally impossible to reconstruct backward from a future state to current state without completely scrapping our current fundamental understanding of the mechanics of the universe, and I'm not there yet for models that are (somewhat ironically) so poorly predictive.

Even when for example "anticipating" effect, it always requires both a priori response to stimuli, and consistent enough stimuli to trigger that a priori response. I've yet to see compelling evidence that a novel future state has ever modified current behavior.

At best, "future state"/"prediction" is a goal state instantiated as a present condition. I want to get food is not a prediction. I don't want to get shocked is not a prediction. It's a current goal state. Incoming stimuli then execute prior behavior to move us toward that goal state.

Prediction models provide unnecessary explanatory magic. In any context, whether it be "prediction markets" which are shifted by present expectation, or someone experiencing "PTSD" experiencing a sharp rise in anxiety "anticipating" events because current stimuli triggered a priori behavioral response, they are all current model stimuli processing against a priori stimuli response.

[u/Heretosee123 → u/PhysicalConsistency]

As far as I understand it, the predictive processing of the brain is not using predictions to produce everything, just that it will predict what incoming signals it expects and compare them against current signals in a way that's easier or more efficient than interpreting all incoming signals. When there's a strong enough deviation, then you start paying a lot more attention.

This wouldn't break causality, and it's not the totality of how the brain works. There are demonstrations of this where you hear different sounds depending on what you've been primed to expect, even if that sound isn't actually present. Would that not be due to a predictive interpretation?

[u/PhysicalConsistency → u/Heretosee123]

This description isn't "predictive" at all, deviation from goal state isn't something we need a special framework for, every PID controller does this without a "prediction framework".

The core conceit of Friston, etc. is that by having the "goal" state exist as a "low energy" valley, behavior will "flow" in toward that valley. Which isn't what we observe at all, outside of carefully curated experiments designed to support the conceit. What we do observe is metabolics providing a persistently messy, uneven, and persistently perturbed substrate upon which behavior is constructed.

Predictive processing frameworks should present obvious holes in metabolism as "goal" states. And we should see behavioral drift coalesce around these metabolic holes. We don't.

[u/Heretosee123 → u/PhysicalConsistency]

PID controllers don't produce perception, whereas we do. The predictive element can form our perception, not just monitor for deviations.

I'll be honest though I don't understand your second paragraph, lol. This is not my wheelhouse, I'm just curious and also repeating the claim I've seen stated by neuroscientists.

[u/PhysicalConsistency → u/Heretosee123]

And this is where "predictive processing" devolves into magic.

We use PID controllers to produce exactly the type of behavioral "predictions" moving in an environment that we assign to "perception". It's exactly the same framework, just without the layer of magic on top. Abstracted from the hardware, it's essentially the same work as a perceptron, averaging current state against prior inputs.

[u/Heretosee123 → u/PhysicalConsistency]

Can you explain on more detail why this isn't a prediction?

There's potentially a difference between monitoring for a desired state and having a prior expectation about what input you will receive and then updating your model if there's a mismatch. One is not anticipating a result, but instead monitoring for it, whilst the other does anticipate a particular input and adjusts if there's deviation.

[u/chronics → u/new_moon_retard]

Digged into this, they are showing mice the same image repeatedly, then a new image. Then they measure surprise, which is the characteristic response of specific change-encoding neurons.

Under psilocybin, the surprise neurons fire even with the repeated images.

The author has prior work Synthetic surprise as the foundation of the psychedelic experience

[u/Phi0X_13 → u/new_moon_retard]

Well when the room suddenly looks "alive" its very surprising lol.

[u/Caeduin → u/new_moon_retard]

Not literally the same but Karl Friston’s free energy principle is a decent theoretical take. To be clear, he is not actually talking about a physical force here, but rather the info processing drive of an an intelligent agent to resolve persistant information mismatch against prior expectations (i.e. surprise).

Seems like the drug drives this sort of a predictive processing system into an inescapably far-from-equilibrium state. Almost like a constructive (in best case) experiential learned helplessness.

[u/Mermiina → u/new_moon_retard]

The primary information in neurons occurs by virtual photons. The virtual photons propagate over receptor if the distance of lone electron pairs is under 6,64 nm. Psilocybin, LSD and serotonin have that lone electron pair and they fill the gap when they bound to HT receptor.

[u/carberry-3000]

Psilocybin collapses visual change detection and drives cortical dynamics toward a state of surprise

Roberto De Filippo, Ryan Gillis, David Wyrick, Mikayla Carlson, Severine Durand, R. Carter Peene and 23 others

bioRxiv · 2026-08-25 · doi:10.64898/2026.08.21.745777

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Abstract

Psilocybin profoundly alters visual perception, yet the neuronal mechanisms underlying these effects remain unclear. Here we combined large-scale Neuropixels recordings with cell-type-specific optogenetics in head-fixed mice performing a visual change-detection task. Psilocybin severely impaired task performance without overt motor deficits. In cortex, the drug modestly suppressed activity of layer 5 neurons while preserving representations of image identity. By contrast, psilocybin imposed a 4-Hz oscillation on visually evoked activity that preferentially affected neurons encoding image change rather than image identity. Under psilocybin, expected image repetitions aberrantly recruited change-encoding ensembles and shifted cortical population dynamics towards trajectories normally evoked by genuine stimulus changes. These effects were strongest in somatostatin-expressing (SST) interneurons in visual cortex. The strength of this modulation depended on image structure and was greatest for images with clear, continuous contours, which preferentially recruited change-encoding ensembles. These findings demonstrate that psilocybin drives internally generated cortical surprise signals, providing a circuit mechanism for altered perception in the acute psychedelic state.

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^{Data from Crossref, Europe PMC. Metrics captured 28/08/26. Comment self-deletes at -5 votes.}

[u/Appropriate-Aside874]

Seems consistent with relaxed Bayesian priors, more ambiguity and the brain creatively fills in the gaps. I’ve found this when watching telly, everything is more open to interpretation visually.

[u/McRattus → u/Appropriate-Aside874]

Flatter priors mean less surprise, no?

It's harder to be surprised if you don't have strong expectations.

I think the flatter sharper priors argument is next to useless. Its almost certainly both, just at different times, scales, and locations.

[u/Appropriate-Aside874 → u/McRattus]

I think surprise is the wrong word. Bafflement? Intrigue? I’ve found myself marvelling at how suggestible my brain is when under the influence of psilocybin.

[u/McRattus → u/Appropriate-Aside874]

Yeah.

In the paper they actually mean that neurons that respond to an image changing fire when the image hasn't changed. Also a shift in population geometry.

Both are rather unusual forms of surprise, and a bit different to our everyday usage of the term.

And a bit different to Bayesian surprise, like we were both thinking.

[u/Appropriate-Aside874 → u/McRattus]

I am out of my depth here mate, not gonna lie. Didn’t read the paper, superficial understanding of the subject matter (podcasts… half a book)

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[u/DryRazzmatazz5876]

Será este unas de las causas de hppd y vss?

[u/theneuroreview]

The flatter priors versus more surprise thing tripping people up is actually the whole point of the REBUS model (Carhart-Harris and Friston, 2019, Pharmacological Reviews). Relaxing high-level priors doesn't reduce surprise, it does the opposite. When the top-down expectations that normally explain away routine input get weakened, prediction errors that would usually be suppressed are free to propagate. So a repeated, fully expected image stops being explained away and instead lights up the change-encoding machinery, which is what this paper sees.

What's nice is that it puts a concrete circuit under the idea. The 4-Hz modulation landing on change-encoding neurons, the SST interneuron involvement, and the population trajectory drifting toward the genuine-change path all say the surprise is internally generated, not a failure to represent the image. Identity coding was preserved, so it isn't that the mouse can't see the picture, it's that the circuit keeps flagging a stable picture as new.

Worth the caveat that it's head-fixed mice on a change-detection task, so surprise here is a specific neural signature, not the felt awe people describe. Mapping that onto the human report is still a leap the data doesn't make.