Front. Hum. Neurosci., 23 May 2017 | https://doi.org/10.3389/fnhum.2017.00245
Looking for the Self: Phenomenology, Neurophysiology and Philosophical Significance of Drug-induced Ego Dissolution
Raphaël Millière (Faculty of Philosophy, University of Oxford, Oxford, United Kingdom)
There is converging evidence that high doses of hallucinogenic drugs can produce significant alterations of self-experience, described as the dissolution of the sense of self and the loss of boundaries between self and world. This article discusses the relevance of this phenomenon, known as “drug-induced ego dissolution (DIED)”, for cognitive neuroscience, psychology and philosophy of mind. Data from self-report questionnaires suggest that three neuropharmacological classes of drugs can induce ego dissolution:
- classical psychedelics,
- dissociative anesthetics and
- agonists of the kappa opioid receptor (KOR).
While these substances act on different neurotransmitter receptors, they all produce strong subjective effects that can be compared to the symptoms of acute psychosis, including ego dissolution. It has been suggested that neuroimaging of DIED can indirectly shed light on the neural correlates of the self. While this line of inquiry is promising, its results must be interpreted with caution.
- First, neural correlates of ego dissolution might reveal the necessary neurophysiological conditions for the maintenance of the sense of self, but it is more doubtful that this method can reveal its minimally sufficient conditions.
- Second, it is necessary to define the relevant notion of self at play in the phenomenon of DIED.
This article suggests that DIED consists in the disruption of subpersonal processes underlying the “minimal” or “embodied” self, i.e., the basic experience of being a self rooted in multimodal integration of self-related stimuli. This hypothesis is consistent with Bayesian models of phenomenal selfhood, according to which the subjective structure of conscious experience ultimately results from the optimization of predictions in perception and action. Finally, it is argued that DIED is also of particular interest for philosophy of mind. On the one hand, it challenges theories according to which consciousness always involves self-awareness. On the other hand, it suggests that ordinary conscious experience might involve a minimal kind of self-awareness rooted in multisensory processing, which is what appears to fade away during DIED.
Hallucinogenic drugs are known to produce profound changes in consciousness. While their immediate effects on perception and mood are well-documented (Halberstadt, 2015), some of their complex effects at higher doses have received less attention until more recently. In particular, a number of hallucinogenic compounds can induce thorough disturbances of self-consciousness, described as a dramatic breakdown of one’s sense of self, a phenomenon commonly referred to as “ego dissolution” (Lebedev et al., 2015). Similar disturbances of self-consciousness are also reported in several psychiatric disorders, specifically in acute psychosis (Bowers and Freedman, 1966; Gouzoulis-Mayfrank et al., 1998; Sass et al., 2013), as well as mystical-type experiences (Baumeister and Exline, 2002; Hood, 2002) and deep meditative states (Dor-Ziderman et al., 2013). However, in these endogenous cases, it is difficult to study the mechanisms of ego dissolution, due to its unpredictability and complex etiology. By contrast, the study of Drug-Induced Ego Dissolution (DIED) in healthy individuals offers a way to track down underlying mechanisms of ego dissolution, which in turn could help us gain a better understanding of the neurobiological basis of the sense of self.
This article presents an interdisciplinary perspective on DIED and its relevance in studying the sense of self, which is a multifaceted and controversial notion. First, the phenomenology of DIED will be described, based on an analysis of available subjective reports and quantitative data from questionnaires. It will be argued that DIED is a valid construct resulting from the use of psychoactive substances with different chemical structures. Second, this article will review current knowledge about the neurophysiology and neuropharmacology of DIED, which, albeit limited, offers promising insights into its neural underpinning. Third, this article will discuss the relevance of DIED for cognitive neuroscience. In particular, it will address methodological issues within studies investigating neural correlates of DIED, and the extent to which neuroimaging can shed light on the neurobiological basis of the sense of self. In addition, this article will examine the hypothesis that DIED consists in a disruption of the “embodied” or “minimal” self (the meaning of which will be discussed later) in light of phenomenological evidence, conceptual analysis and recent neurocomputational models of selfhood. Finally, it will be suggested that the study of DIED can also contribute to contemporary philosophical debates on self-awareness.
 The κ-opioid receptor (KOR) is a protein that in humans is encoded by the OPRK1 gene. The KOR is one of four related receptors that bind opioid-like compounds in the brain and are responsible for mediating the effects of these compounds. These effects include altering nociception, consciousness, motor control, and mood.
The KOR is a type of opioid receptor that binds the opioid peptide dynorphin as the primary endogenous ligand (substrate naturally occurring in the body). In addition to dynorphin, a variety of natural alkaloids, terpenes and other synthetic ligands bind to the receptor.”
widely distributed in the brain, spinal cord (substantia gelatinosa), and in pheripheral tissues. High levels of the receptor have been detected in the prefrontal cortex, periaqueductal gray, raphe nuclei (dorsal), ventral tegmental area, substantia nigra, dorsal striatum (putamen, caudate), ventral striatum (nucleus accumbens, olfactory tubercle), amygdala, bed nucleus stria terminalis, claustrum, hippocampus, hypothalamus, midline thalamic nuclei, locus coeruleus, spinal trigeminal nucleus, parabrachial nucleus, and solitary nucleus.
[is claustrum involved?: “Theories suggest the claustrum may act to bind and integrate multisensory information, or else to encode sensory stimuli as salient or nonsalient (Mathur, 2014). One theory suggests the claustrum harmonizes and coordinates activity in various parts of the cortex, leading to the seamless integrated nature of subjective conscious experience (Crick and Koch, 2005; Stiefel et al., 2014).” (Claustrum: thin, irregular sheet of neurons that is attached to the underside of the neocortex … considered by some sources to be part of the basal ganglia. … contains a great deal of longitudinal connections between its neurons that could serve to synchronize the entire anterior-posterior extent of the claustrum. Francis Crick and Christof Koch have compared the claustrum to the conductor of an orchestra, referring to its regulatory role in consciousness and cognition. … widespread coordination of the cerebral cortex, using synchronization to achieve a seamless timescale between both the two cortical hemispheres and between cortical regions within the same hemisphere, resulting in the seamless quality of conscious experience.”