Classic Hallucinogens and Mystical Experiences : Phenomenology and Neural Correlates, Frederick S. Barrett & Roland R. Griffiths, 2018

Classic Hallucinogens and Mystical Experiences : Phenomenology and Neural Correlates

Frederick S. Barrett, Roland R. Griffiths

Current Topics in Behavioral Neurosciences, 2018, 36, 393–430.

doi : 10.1007/7854_2017_474



This chapter begins with a brief review of descriptions and definitions of mystical-type experiences and the historical connection between classic hallucinogens and mystical experiences. The chapter then explores the empirical literature on experiences with classic hallucinogens in which claims about mystical or religious experiences have been made. A psychometrically validated questionnaire is described for the reliable measurement of mystical-type experiences occasioned by classic hallucinogens. Controlled laboratory studies show that under double-blind conditions that provide significant controls for expectancy bias, psilocybin can occasion complete mystical experiences in the majority of people studied. These effects are dose-dependent, specific to psilocybin compared to placebo or a psychoactive control substance, and have enduring impact on the moods, attitudes, and behaviors of participants as assessed by self-report of participants and ratings by community observers. Other studies suggest that enduring personal meaning in healthy volunteers and therapeutic outcomes in patients, including reduction and cessation of substance abuse behaviors and reduction of anxiety and depression in patients with a life-threatening cancer diagnosis, are related to the occurrence of mystical experiences during drug sessions. The final sections of the chapter draw parallels in human neuroscience research between the neural bases of experiences with classic hallucinogens and the neural bases of meditative practices for which claims of mystical-type experience are sometimes made. From these parallels, a functional neural model of mystical experience is proposed, based on changes in the default mode network of the brain that have been observed after the administration of classic hallucinogens and during meditation practices for which mystical-type claims have been made.

Keywords : psilocybin; hallucinogens; meditation; mystical experiences; neural model; default mode network; medial prefrontal cortex; posterior cingulate; angular gyrus; inferior parietal lobule


1. Introduction

Reports of mystical-type experiences date back many centuries (e.g. in the case of Rumi or St. Teresa of Avila), if not millennia (i.e. in the case of Plotinus) (Stace, 1960a). Mystical experiences have occurred in the course of structured spiritual or religious practices as well as in cases in which there was no direct intention to have such an experience. Mystical experiences are uniquely interesting and important to study because they are sometimes associated with abrupt, substantial, and sustained changes in behavior and perception (Miller & C’de Baca, 2001). Furthermore, the authoritative sense of interconnectedness and sacredness that defines such experiences suggest that mystical experiences may be foundational to the world’s ethical and moral systems (Huxley 1947). Despite their apparent importance, the unpredictability and low probability of “naturally occurring” mystical-type experiences, whether they occur in religious or non-religious contexts, has made them inherently difficult to study in controlled empirical research.

While there are countless reports of profound spiritual and mystical experiences that have occurred in the absence of psychoactive substances, historical evidence abounds for the role of psychoactive substances in ceremonial approaches to facilitating such experiences (Schultes, Hofmann, & Rätsch, 2001). Further, descriptions of naturally occurring mystical experiences (Stace, 1960b) are strikingly similar to profound spiritual experiences occasioned by hallucinogenic substances (Roberts, 2001). Experimental investigations have begun to utilize classic hallucinogens to study the reliability, characteristics, subjective nature, and behavioral consequences of mystical-type experiences (Pahnke, 1963; Griffiths, Richards, McCann, & Jesse, 2006; Griffiths et al., 2011; Garcia-Romeu et al., 2015). Classic hallucinogens are a structurally diverse group of compounds that bind at 5-HT2A serotonin receptors and produce a unique profile of changes in thoughts, emotions, and perceptions, often including profound alterations in the perception of reality, that are rarely experienced except in dreams, naturally occurring mystical experiences, and acute psychosis. The use of classic hallucinogens makes the study of mystical experiences more tractable because classic hallucinogens can be administered under double-blind conditions and can occasion mystical experiences with high probability (Griffiths et al., 2006; Griffiths et al., 2011). Classic hallucinogens allow for prospective and controlled exploration of such experiences, and provide a degree of neurobiological specificity and mechanistic understanding that is not possible in correlational or descriptive studies, or in reviews of present-day or historical case reports.

The following section of this chapter reviews descriptions and definitions of mystical-type experiences. Evidence of the historical connection between classic hallucinogens and mystical experiences is then presented. The chapter then reviews empirical evidence of mystical experiences occasioned by classic hallucinogens and the potential therapeutic benefits of such experiences. The chapter ends with an exposition of a functional neural model of mystical experience that is based on changes in the default mode network of the brain that have been observed after the administration of classic hallucinogens and during meditation practices which are sometimes associated with mystical-type experiences.

2. What are Mystical Experiences ?

“[Mystical experiences are] those peculiar states of consciousness in which the individual discovers himself to be one continuous process with God, with the Universe, with the Ground of Being, or whatever name he may use by cultural conditioning or personal preference for the ultimate and eternal reality”
(Watts, 1970)

The theological and philosophical literatures have primarily taken descriptions of experiences as their source data for the exploration of mystical experiences. The theological literature on mystical experiences is based on accounts of prophets, saints, and the practices of mystic sects within religious traditions. Mystic sects exist within all major world religions. These sects are lineages of individuals who have organized around a spiritual practice within their culture and religion, with characteristic lifestyles, teachings, and traditions that instruct the individual and provide a supportive setting for the individual to achieve a deeper connection with the God of their understanding. In this fashion, mystics may be considered “empirical” theologians (Huxley, 1947). Sufism is a mystical sect within the religion of Islam, while Kabbalists explore mysticism in the context of Judaism. Individuals from various religious traditions, including Christian (e.g. Meister Eckhart from the 13th century, St. Teresa of Avila and St. John of the Cross from the 16th century), Islamic (e.g. Rumi and Saadi from the 13th century), and Jewish (e.g. Maimonides of the 12th century) traditions, are considered to be mystics. Some Hindu and Buddhist meditation practices that focus on non-dual experiences likely increase the probability of mystical-type experiences (Stace, 1960a).