Psychedelics And Our Brains' Predictive Processing
Updated: Aug 14, 2021
The idea that our brains are in essence prediction machines dates back to the 19th century. What this means is that scientists have long believed that our brains do not necessarily process the reality in our environment by processing every possible datapoint but rather, we process a small portion of the reality and predict the rest based on past experiences to improve our processing speed.
A recent in-depth article by Genetic Literacy Project explores the science of our perception and the role of psychedelics in helping scientists better understand how our brains process our unfolding reality.
The simplest way to understand our brain's predictive qualities is through optical illusion tests like the one demonstrated below where some perceive the vase and others see two people facing each other. "In this view of perception, “the brain is actively … creating hypotheses that are the best explanation for the sensory samples that it’s receiving,” says computational neuroscientist Karl Friston of University College London."
The article goes on to explain that the brain's predictive processing is a byproduct of past experiences. The higher the confidence level of a given prediction signal based on past experience, the more likely we are to perceive a given outcome over possibilities with a lower confidence level.
"An important aspect of predictive processing is that each hypothesis generated by a level in the hierarchy is associated with a notion of confidence in the hypothesis, which in turn is based on prior expectations. The higher the confidence, the more a given level ignores error signals from the level below. The lower the confidence, the more a given level listens to upward-moving error signals."
Experienced psychonauts have long reported experiencing lasting changes in how they perceive their reality following a psychedelic experience. The article goes on to explore the possibility that psychedelics alter our brain's predictive processing.
"Could psychedelics be altering our perception of reality by messing with this process? Friston and Robin Carhart-Harris, a psychologist and neuroscientist at Imperial College London, think so. In 2019, they put forward a model called REBUS, for “relaxed beliefs under psychedelics.” According to their model, psychedelics reduce the brain’s reliance on prior beliefs about the world. “We feel them with less confidence,” says Carhart-Harris. “They are less reliable under psychedelics.”
If that’s what psychedelics do, one result could be an increase in cognitive flexibility. Conversely, blocking the receptors in the brain that are activated by psychedelics might do the opposite — make beliefs more rigid."
"Of course, psychedelic hallucinations are not only visual. They can involve all types of altered perceptions. In 2017, for example, neuropsychologist Katrin Preller of the University Hospital for Psychiatry Zurich in Switzerland and colleagues found that people listening to music that they normally considered meaningless or neutral felt heightened emotions and attributed an increased sense of meaningfulness to the music while on LSD.
Friston argues that these altered perceptions extend even to our sense of self, which in the predictive processing framework is based on the brain’s internal models of all aspects of our own being. Psychedelics would, again, loosen the hold of these internal models. “You now lose a precise sense of self,” says Friston. Indeed, a survey by Carhart-Harris and colleagues suggests that a breakdown of the boundaries of the self could be one explanation for why some people on psychedelics report mystical feelings of a sense of unity."
Psychedelic studies are offering a new and exciting opportunity for scientists to further explore whether the predictive processing model is an accurate representation of how our brains function or are there other factors impacting how we see and experience our unfolding reality.