Oneirogen

An oneirogen, from the Greek ὄνειρος óneiros meaning "dream" and gen "to create", is a substance that induces a dream-like state of consciousness. Oneirogens function by altering neural processing in a way that shifts the brain from bottom-up sensory input to top-down generative activity, resembling the mechanisms involved in dreaming. This neural shift is associated with increased internal imagery and reduced responsiveness to external stimuli. Psychedelics—particularly those acting on the 5-HT2A receptor—produce oneirogenic effects by promoting this altered balance of neural signaling.