Perception may alternate between favoring either top-down predictions or bottom-up evidence of its senses when the default mode network is inacavtive
The classic dilemma in psychedelic research is whether the tripping brain, unconstrained, favors top-down predictions or bottom-up evidence of its senses. You do often find a kind of impetuousness or overzealousness with the brain on the part of the priors, as when you see faces in the clouds. Being eager to make sense of the data rushing in, the brain leaps to erroneous conclusions and, sometimes, a hallucination results. The paranoid does much the same thing, ferociously imposing a false narrative on the stream of incoming information.
But in other cases, the default mode network opens wide to admit lots more information, unedited and sometimes welcome because decreased default mode network activity may loosen the inhibitory mechanims in the brain. People who are color-blind report being able to see certain colors for the first time when on psychedelics, and there is research to suggest that people hear music differently under the influence of these drugs. They process the timbre, or coloration, of music more acutely—a dimension of music that conveys emotion.
Psychedelics render the brain’s usual handshake of perception less stable and more slippery. The tripping brain may “slip back and forth” between imposing its priors and admitting the raw evidence of its senses. There are moments during the psychedelic experience when confidence in our usual top-down concepts of reality collapses, opening the way for more bottom-up information to get through the filter of the default mode network. But when all that sensory information threatens to overwhelm us, the brain furiously generates new concepts (crazy or brilliant, it hardly matters) to make sense of it all—and so you might see faces coming out of the rain. That’s the brain doing what the brain does; working to reduce uncertainty by, in effect, telling itself stories.
Ordinary waking consciousness is more firm than other conscious states because of a continual process of reality testing, and by adulthood, the brain has gotten very good at observing and testing reality and developing reliable predictions about it that optimize our investments of energy (mental and otherwise) and therefore our chances of survival. Uncertainty is a complex brain’s biggest challenge, and the process in which The brain’s perceptual systems actively and pre-consciously interpret and edit their input has evolved to help us reduce it.
References
- Pollan, Micheal. (2018). How to Change Your Mind Chapter 5. The Neuroscience of Your Brain on Psychedelics (Location 4230). New York, NY: Penguin Random House.
Metadata
Type:🔴 Tags: Biology / Neuroscience / Biochemistry / Neurochemistry / Pharmacology Status:☀️