Scott Alexander has a cool theory that unifies Bayesian inference, low-level behaviour like neurotransmitter levels and high-level behaviour like learning, making decisions and different sensory phenomena (some of the posts explain autism and schizophrenia):

* https://slatestarcodex.com/2017/09/05/book-review-surfing-un...

* https://slatestarcodex.com/2016/09/12/its-bayes-all-the-way-...

* https://astralcodexten.substack.com/p/towards-a-bayesian-the...

* https://astralcodexten.substack.com/p/trapped-priors-as-a-ba...

The core concept is called predictive coding, which suggests that the brain is constantly generating and updating a model of the world in a top-down and bottom-up manner: https://en.wikipedia.org/wiki/Predictive_coding

Disclaimer: epistemic status = very speculative.