A dual-receptor model of serotonergic psychedelics

Serotonergic psychedelics have been identified as promising next-generation therapeutic agents in the treatment of mood and anxiety disorders. While their efficacy has been increasingly validated, the mechanism by which they exert a therapeutic effect is still debated. A popular theoretical account is that excessive 5-HT2a agonism disrupts cortical dynamics, relaxing the precision of maladaptive high-level beliefs and making them more malleable and open to revision. We extend this perspective by developing a simple energy-based model of cortical dynamics based on predictive processing which incorporates effects of neuromodulation. Using this model, we propose and simulate hypothetical computational mechanisms for both 5-HT2a and 5-HT1a agonism. Results from our model are able to account for a number of existing empirical observations concerning serotonergic psychedelics effects on cognition and affect. Using the findings of our model, we provide a theoretically-grounded hypothesis for the clinical success of LSD, psilocybin, and DMT, as well as identify the design space of biased 5-HT1a agonist psychedelics such as 5-MeO-DMT as potentially fruitful in the development of more effective and tolerable psychotherapeutic agents in the future.