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The Mind-Melting Science of What Shrooms Do to Your Brain

No one’s exactly sure why psilocybin makes you see goats in your bathroom, but it might have something to do with how your brain processes reality

The human brain goes into full weirdo mode after a handful of shrooms. It forgets how time works. It turns blank walls into geometrical works of art. It makes you believe the cucumber in your fridge is an actual God. (Or was that just me?) But why? What do shrooms do to your brain? 

It’s a complicated question, one that will challenge your perception of reality.

The surface-level explanation, according to researcher and philosopher Chris Letheby, author of Philosophy of Psychedelics, is that psilocybin, the psychedelic compound in magic mushrooms, stimulates serotonin 2A receptors in your brain. In a way we don’t yet fully understand, this induces the psychedelic effects commonly associated with mushies — hallucinations, transcendence of time and space, whatever’s going on between my cucumber and me.

But what happens in the thick of those two occurrences — provocation of the serotonin 2A receptors and your tripping balls — is a major mystery. That said, Cal State University, Fullerton neuroscientist Luke McGowan says that predictive processing, a framework for understanding how your brain works — and how psychedelics disrupt it — can provide some compelling clues.

In short, predictive processing says that, as you trample through life, your brain becomes increasingly familiar with how the world around you works. Once it’s gathered enough data and formulated models based on what it’s seen, your mind begins the constant process of making assumptions about incoming sensory information — sights, sounds, smells — to help you comprehend your relationship with the world. Or as McGowan says, “Your brain is a guessing machine.”

The guesses it makes are based on a hierarchical series of assumptions, some of which your mind is more confident in than others. For instance, your higher-order belief that fairies don’t exist will do it’s best to overrun your lower-order belief that you just saw a fairy out of the corner of your eye.

Here’s another example: A coat hanger in your bedroom momentarily appears to be a person. Then, one of your brain’s higher-order models — your previous knowledge of everything in your room, and the fact that nobody’s ever popped up in your bedroom in the middle of the night — tells your eyes that they’re mistaken. As a result, your perception reverts back to that of just a coat hanger, and you can soundly get some sleep.

This is where psilocybin comes in, and Letheby points to a theoretical model called REBUS — “relaxed beliefs under psychedelics” — to help explain its plausible impact on the brain. In short, REBUS suggests that shrooms decrease your confidence in all those assumptions we just covered. 

For instance, if your eyes sent a signal to your sober brain saying they saw your walls moving, it would respond: “No, your walls aren’t moving.” But under the effects of some shroom tea, your brain wouldn’t be so sure. It may believe your eyes, and as a result, it’ll send out signals so your walls actually start dancing (or rather, you perceive them to be dancing). 

So, in very, very simple terms, psilocybin interrupts your perception of the world around you, and as a result, you’ll essentially manifest that new reality in your head.

None of this is to say that the world around you isn’t real. “It’s just that our experience of that world is always this internal kind of virtual simulation process,” Letheby says. There are actual, animate objects around you, but your concept of them helps shape your perception. 

Psilocybin simply makes your brain either second guess its preconceived notions or acknowledge new ones. It allows your mind to temporarily go back to its blanker self, before it was indoctrinated by experiences. Or as Letheby says, “It sort of serves as a reset for the mind.”

This is where shrooms flaunt their potential as therapeutics for disorders like anxiety, depression, addiction and PTSD — all issues that stem from infinite loops of negative thinking. “You get kind of entrenched in these sort of perceptual and psychological echo chambers, where you have certain models of who you are,” Letheby says.

But shrooms can give your brain a chance to unlearn those assumptions. Under the right therapeutic conditions, McGowan says a psilocybin trip may allow you to assign new levels of confidence to your abilities, whether that be kicking a compulsion or cutting ties with a trauma.

Interestingly, studies suggest that these effects may last long-term and could potentially help people overcome psychological issues in a very short period of time. There’s plenty of anecdotal evidence to support this, too: Famed mycologist Paul Stamets, for instance, freed himself from a lifelong stutter thanks to a large dose of magic mushrooms.

Still, Letheby says we need more research to truly harness psilocybin’s potential, but if we can manage to use it in calculated ways to help relieve people from their psychological burdens, it’ll be a “game-changer in psychiatry.”

Now can somebody please explain to me why there’s a cucumber shrine in my bedroom?

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