Introduction
At sufficiently high doses, all classical psychedelics can produce an experience that users describe as the temporary dissolution of the boundary between self and world -- a loss of the sense of being a separate individual observing reality from behind the eyes. This phenomenon, known as ego dissolution, is the most distinctive and therapeutically significant aspect of the psychedelic experience. It is closely related to what researchers call the "mystical experience" -- a state characterized by unity, transcendence, sacredness, deeply felt positive mood, and a sense of encountering ultimate reality. Understanding ego dissolution has moved from philosophical speculation to quantitative neuroscience.
Defining and Measuring the Experience
The experience of ego dissolution exists on a spectrum. At the mild end, users report a loosening of habitual thought patterns and a sense that the boundaries of the self are becoming more permeable. At the profound end, the experience involves a complete loss of personal identity -- the sense that "I" exists disappears entirely, replaced by a state of undifferentiated awareness or unity with all of existence.
The Mystical Experience Questionnaire (MEQ30): Roland Griffiths and colleagues at Johns Hopkins developed the 30-item revised Mystical Experience Questionnaire, validated in a 2015 study using data from controlled psilocybin administration. The MEQ30 measures four factors: mystical (sense of internal and external unity), positive mood, transcendence of time and space, and ineffability/sacredness. A "complete mystical experience" is defined as scoring above 60% on all four factors.The Ego Dissolution Inventory (EDI): Nour et al. at Imperial College London published the EDI in 2016 (Frontiers in Human Neuroscience), an 8-item self-report scale specifically designed to measure ego dissolution. The scale distinguishes between ego dissolution (the experience of the boundaries of the self dissolving) and ego inflation (an aggrandized sense of self), providing more precise measurement of the construct.
