I have a habit of jumping toward the next promising thing the moment I hear about it. That is what happened when psychedelics started making their way back into clinical conversation, this time with serious money behind them, rigorous protocols, and trials designed to convince regulatory agencies that these compounds deserved a second look. Posttraumatic stress disorder (PTSD) was at the center of it. I went immediately to get trained, had my own experiences, and came away convinced that the benefits were real, and that what made them real was not the substance alone but everything surrounding it.
As I was finishing my training, something else was already happening. More and more clients were reporting that they had tried psychedelics on their own, or were planning to. The frustrations were immediate and layered. I could not refer them to a licensed provider because the treatments were not yet legal. I found myself explaining, over and over, that preparation matters, that without it, the experience is far less likely to be therapeutic. I wanted them to understand that the protocols existed for a reason: the doses are not arbitrary, the setting is not incidental, and taking MDMA at a concert does not constitute a therapeutic session.
The reality, though, was moving faster than the regulation. People were having trips without preparation, without support, without integration—and most of them were not getting the results they had hoped for.
That gap sent me deeper into the question of how these substances actually work. What I found there genuinely excited me.
Your brain is not a camera
One of the theories I have adopted for its revolutionary implications holds that the brain is better understood as a prediction engine. Rather than passively receiving information, it is constantly generating hypotheses about what is happening—what you are seeing, feeling, hearing, and experiencing—and then comparing those predictions to incoming signals from the senses and the body. When reality matches the prediction, nothing much changes. When it doesn’t, the brain registers what neuroscientists call a prediction error, and it updates its internal model accordingly.
This framework, known as the Free Energy Principle, was developed by neuroscientist Karl Friston, and it’s becoming one of the most influential theories in contemporary cognitive science. The core idea is simple, even when it is based on very sophisticated calculations: The brain’s fundamental job is to minimize surprise. It does this not by knowing everything but by becoming very good at predicting and by continuously refining those predictions in the light of experience.
When we lose the capacity to update
To understand how this applies to conditions like depression, anxiety, or PTSD, it helps to think of the brain as a hierarchy of predictions.
At the top sit high-level beliefs: deep, generalized convictions about yourself, other people, and how the world works. These are the executive layer, the conclusions drawn from a lifetime of experience.
At the bottom sit the raw data: sensory signals, bodily sensations, the moment-to-moment input streaming in from the environment.
In a well-functioning brain, these levels are in ongoing dialogue. Top-down beliefs shape how incoming information is interpreted. But when new information is strong enough and clear enough, it updates the beliefs. The model stays flexible. It learns continuously, updating the information it will use for the next prediction.
In many forms of psychological suffering, particularly traumatic experiences that remain active, this dialogue breaks down in a specific way. The high-level beliefs become what researchers call hyper-precise priors: rigid, over-weighted convictions that refuse to be revised, no matter what the incoming evidence suggests.
A client comes to mind. When I met them, they were in the grip of chronic depression, holding the deep conviction that they were fundamentally unlovable. When a friend reached out warmly, a colleague offered genuine praise, or a partner expressed care, these were prediction errors, incoming signals that contradicted the existing model, but they had no effect. The belief was so heavily weighted that it overrode those experiences. The brain didn’t update. Instead, it reinterpreted, dismissed, or simply ignored the disconfirming evidence. The loop closed in on itself.
Psychedelics Essential Reads
What others call resistance is, at its core, a systems problem. The brain is doing its job: minimizing free energy, reducing surprise, maintaining its model. But it is doing it with a model that is distorted, outdated, and deeply costly to the person living inside it.
Where psychedelics come in
In 2019, Robin Carhart-Harris and Karl Friston proposed a model that links psychedelic therapy directly to this framework. They called it REBUS: relaxed beliefs under psychedelics.
The core claim is precise. Psychedelic compounds like psilocybin and LSD act primarily on serotonin receptors that are densely concentrated in the brain’s high-level predictive networks, including the default mode network, the system most associated with self-referential thought, narrative identity, and the consolidated sense of who we are. By disrupting the synchronized activity of these networks, psychedelics temporarily loosen the grip of those top-down priors. The executive layer, so to speak, stops issuing orders.
The effect moves through the system in sequence. With the top-down suppression lifted, lower-level signals, raw sensory input, embodied experience, and emotional material that have been filtered out or overridden for years can finally surface. Memories return with unusual clarity. Emotions arrive with unusual immediacy. Connections form between regions of the brain that rarely communicate under ordinary conditions. The brain enters a state of heightened plasticity, moving through mental territory that its ordinary architecture had rendered inaccessible.
One image captures this well: Imagine a snowy hill where a sled has traveled the same path so many times that the grooves are deep and fixed. Steering is no longer a choice; the sled simply follows the channel it has always followed. Psychedelics act like a fresh snowfall. The grooves soften. The hill opens. And if what happens during that window is met with skilled therapeutic support, the sled can find a new path when it moves again.
This is why the integration phase, the therapeutic work that follows the psychedelic experience, matters so much. The loosening of priors creates an opening, but it does not determine what fills it. That is the work of therapy: helping the person make use of what became available, building a more flexible, more accurate, and more compassionate internal model before the architecture re-consolidates. The trip alone is not what will make that brain reorganize in a more flexible and optimal way.
