title: Ego-Dissolution and Psychedelics: Validation of the Ego-Dissolution Inventory (EDI).
abstract: OBJECTIVE
  The experience of a compromised sense of "self", termed ego-dissolution, is a key feature of the psychedelic experience. This study aimed to validate the Ego-Dissolution Inventory (EDI), a new 8-item self-report scale designed to measure ego-dissolution. Additionally, we aimed to investigate the specificity of the relationship between psychedelics and ego-dissolution.
  
  
  METHODS
  Sixteen items relating to altered ego-consciousness were included in an internet questionnaire; eight relating to the experience of ego-dissolution (comprising the EDI), and eight relating to the antithetical experience of increased self-assuredness, termed ego-inflation. Items were rated using a visual analog scale. Participants answered the questionnaire for experiences with classical psychedelic drugs, cocaine and/or alcohol. They also answered the seven questions from the Mystical Experiences Questionnaire (MEQ) relating to the experience of unity with one's surroundings.
  
  
  RESULTS
  Six hundred and ninety-one participants completed the questionnaire, providing data for 1828 drug experiences (1043 psychedelics, 377 cocaine, 408 alcohol). Exploratory factor analysis demonstrated that the eight EDI items loaded exclusively onto a single common factor, which was orthogonal to a second factor comprised of the items relating to ego-inflation (rho = -0.110), demonstrating discriminant validity. The EDI correlated strongly with the MEQ-derived measure of unitive experience (rho = 0.735), demonstrating convergent validity. EDI internal consistency was excellent (Cronbach's alpha 0.93). Three analyses confirmed the specificity of ego-dissolution for experiences occasioned by psychedelic drugs. Firstly, EDI score correlated with drug-dose for psychedelic drugs (rho = 0.371), but not for cocaine (rho = 0.115) or alcohol (rho = -0.055). Secondly, the linear regression line relating the subjective intensity of the experience to ego-dissolution was significantly steeper for psychedelics (unstandardized regression coefficient = 0.701) compared with cocaine (0.135) or alcohol (0.144). Ego-inflation, by contrast, was specifically associated with cocaine experiences. Finally, a binary Support Vector Machine classifier identified experiences occasioned by psychedelic drugs vs. cocaine or alcohol with over 85% accuracy using ratings of ego-dissolution and ego-inflation alone.
  
  
  CONCLUSIONS
  Our results demonstrate the psychometric structure, internal consistency and construct validity of the EDI. Moreover, we demonstrate the close relationship between ego-dissolution and the psychedelic experience. The EDI will facilitate the study of the neuronal correlates of ego-dissolution, which is relevant for psychedelic-assisted psychotherapy and our understanding of psychosis.
authors.affiliation: Psychiatric Imaging Group, MRC Clinical Sciences Centre, Imperial College LondonLondon, UK; Institute of Psychiatry Psychology and Neuroscience, King's College LondonLondon, UK.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Nour
authors.affiliation: Faculty of Medicine, Centre for Neuropsychopharmacology, Division of Brain Sciences, Imperial College London London, UK.
authors.forename: Lisa
authors.initials: L
authors.lastname: Evans
authors.affiliation: Faculty of Medicine, Centre for Neuropsychopharmacology, Division of Brain Sciences, Imperial College London London, UK.
authors.forename: David
authors.initials: D
authors.lastname: Nutt
authors.affiliation: Faculty of Medicine, Centre for Neuropsychopharmacology, Division of Brain Sciences, Imperial College London London, UK.
authors.forename: Robin L
authors.initials: RL
authors.lastname: Carhart-Harris
keywords: ego boundaries; ego death; ego disintegration; ego dissolution; hallucinogen; mystical experience; psychedelic; self disturbance