The term 'psychedelic' was coined in 1956 from Greek roots meaning 'soul-manifesting' or 'soul-illuminating,' intended to name a drug category defined by its ability to induce a characteristic subjective state. This study examined the main subjective effects of psilocybin, ketamine, and MDMA. Over two hundred participants rated items about their experiences with all three drugs. Factor analyses revealed three or four independent dimensions of subjective experience. A machine learning classifier successfully predicted which drug a person had taken from the effects reported, confirming that the three drugs produce categorically distinct experiences: psilocybin induces visions and psychological insight, ketamine induces dissociation, and MDMA induces pro-social feelings such as love. Psilocybin is thus an exemplar psychedelic drug, definable by its induction of a psychedelic state characterized by visions and insight.
Neuroscientific theories of consciousness must address how separate micro-units of information combine into a single, unified conscious experience—the phenomenal binding problem. This paper examines how Integrated Information Theory (IIT) v4.0 offers a solution by proposing that particular entities called 'complexes' define existence. While this works in a static framework, it creates difficulties when applied to dynamic systems. The authors identify a dilemma for IIT: non-local entity transitions versus contiguous selves, termed the 'dynamic entity evolution problem.' Three potential ways IIT could dissolve this dilemma are described. The paper contributes to IIT's shift from static to dynamic analysis.