2. We put forward the ‘Oneirogen Hypothesis,’ arguing that psychedelics cause hallucinations because they hijack a system ordinarily used for learning in the brain.

3. An ‘oneirogen’ is a compound that makes neural activity more dream-like. We propose that psychedelics shift neural activity towards a regime normally reserved for replay during sleep, used for learning. To model this form of learning, we use the classic Wake-Sleep algorithm (Hinton et al. 1995).