Serotonin and Fasting

June 15, 2020

This is a continuation of the discussion of serotonin and dopamine begun on this page. I want to talk about fasting.

I’m fascinated by the fact that 5-HT2A appears to be the mechanism for the antidepressant effects of acute fasting in rodents. Fasting is famously associated with religious experiences, and some of the big names in religion (Jesus, the Buddha) were quite into it. But it also seems to me that if you’re short on food, you may need to do some learning, some lateral thinking, or some literal exploration. I’m inclined to guess that this was the original use of these serotonin receptors. I could be completely wrong. But I can’t remember anyone else arguing this; I’d love to hear of anything, so do let me know if you know anything about this.

What are you trying to argue?

I’m speculating that acute fasting was the original trigger for the 5HT-2A receptor, and the purpose was to put the brain into exploratory/learning mode. It caused you to go on a quest for food, essentially, modulating exploratory behaviour. This is the exploratory half of the equation I described here.

I suspect near-death experiences evolved later and used the same system. Maybe near-death experiences flood the brain with serotonin to put it in a massively plastic state as a last gasp attempt at saving the life of the organism (“Try something super surprising, you’ve got nothing to lose!”). Or maybe becoming extremely chill and “one with the universe” when you’re badly sick or injured makes it more likely your friends will save you than if you’re screaming bloody murder.

Later, religions figured out methods to trigger this learning mechanism (via iconography, patterns, rites of passage, etc). They used this plasticity to bind larger groups of people into bigger communities, and to encumber them with rules.

At some point before or after that, humans noticed that while many mushrooms kill you slowly, others seem to pull the learning/near-death experience trigger. And finally, Hofmann figured out how to put all this on a piece of paper.

Dopamine seems the more obvious case. It makes you crave and consequently seek basic necessities like food, warmth, sex. But in a certain sense, given its role in addiction, it has a tendency to make you “double down” on certain stimuli. The addicted brain can be very good at seeking, but it is not particularly expansive/exploratory. The link between addiction and exploitation seems fairly straightforward.

I have another theory about the link between dopamine, effort, and serotonin, but that will have to wait for another time.

Bryan Kam

I'm Bryan Kam. I'm thinking about complexity and selfhood. Please sign up to my newsletter, follow me on Mastodon, or see more here.