Thank you Tom!

Special thanks to you @sergedumoulin.net for allowing this to happen!! As supervisor it would have been much easier for you to say 'no' to such a complex and potentially risky study. But you had the evidence-based open mindedness and courage to go through with it. I am very grateful for that 🙏

Thank you Evan!

Thank you Anirudh!

Thanks Tomas! Couldn't have done it without you :D

From founding the Amsterdam Psychedelic Research Association (APRA) in 2017 to leading the first-ever neuroimaging study with a classic psychedelic in Amsterdam, this paper represents the closing of a circle and truly means a lot to me. I hope you find it interesting :)

Thank you for reading! I am grateful to all coauthors (Gilles de Hollander, Nina Vreugdenhil, Tomas Knapen, Serge Dumoulin) and study participants, without whom none of this would have been possible.

Indeed, we speculate that the butterfly-effect cascading from such a relatively simple, but profound and pervasive computational change, may explain the broad variety and apparent paradoxicality of psychedelic effects.

Now, imagine what could happen to your subjective experience if a fundamental computation for contextual information-processing was altered throughout many, recurrently interacting levels of the brain's functional hierarchy, from visual, to temporal, to semantic processing...

Divisive normalization is not only present in vision; rather, it is considered a 'canonical neural computation' implementing contextual processing in a variety of sensory and cognitive domains. nature.com/articles/nrn...

In other words, we found that psilocybin altered a fundamental computational building block of contextual processing in the human brain: divisive normalization, particularly in the form of visual surround suppression.

Enter the divisive normalization population receptive field model. The parameter governing surround suppression systematically dropped with psilocybin! This could not be explained by noise or HRF changes alone, which are also included in the model. 🤖

This hinted at a potentially deep computational shift, occurring already at low levels of the brain functional hierarchy. So how can we capture it and make sure it’s not all noise or blood-flow changes?

To find out, we scanned participants with 7T fMRI while showing sweeping high-contrast bars. Key result: psilocybin systematically reduced surround suppression, a key mechanism to optimize contextual neural computations, in early visual areas! 🧠

This wasn’t because participants got worse at the task: perceptual noise was unchanged. The effect of psilocybin was specific to contextual perception! So what’s happening in the brain?

First, we looked at visual perception using the Ebbinghaus illusion, a classic example of how context shapes what we perceive. The contextual surround illusion got systematically stronger! It's not just a figure of speech: we literally see the world differently with psilocybin👁️

thank you for sharing Matt!

thank you @manojdoss.bsky.social ! will add ref :)