Hallucinations Under Psychedelics and in the Schizophrenia Spectrum

An Interdisciplinary and Multiscale Comparison

Pantelis Leptourgos; Martin Fortier-Davy; Robin Carhart-Harris; Philip R. Corlett; David Dupuis; Adam L. Halberstadt; Michael Kometer; Eva Kozakova; Frank LarØi; Tehseen N. Noorani; Katrin H. Preller; Flavie Waters; Yuliya Zaytseva; Renaud Jardri

Disclosures

Schizophr Bull. 2020;46(6):1396-1408. 

In This Article

Abstract and Introduction

Abstract

The recent renaissance of psychedelic science has reignited interest in the similarity of drug-induced experiences to those more commonly observed in psychiatric contexts such as the schizophrenia-spectrum. This report from a multidisciplinary working group of the International Consortium on Hallucinations Research (ICHR) addresses this issue, putting special emphasis on hallucinatory experiences. We review evidence collected at different scales of understanding, from pharmacology to brain-imaging, phenomenology and anthropology, highlighting similarities and differences between hallucinations under psychedelics and in the schizophrenia-spectrum disorders. Finally, we attempt to integrate these findings using computational approaches and conclude with recommendations for future research.

Introduction

Hallucinations, that is, percepts without corresponding stimulus, are common in psychiatric disorders (eg, schizophrenia spectrum disorders, a heterogeneous category with variable course and expressions; henceforth SCZs), in neurological disorders (eg, Parkinson's disease, Lewy body dementia), while they can be observed in the general population too. They are also engendered by psychotomimetic drugs, including serotonergic agonists (ie, psychedelics). Since the nineteenth century, scientists have posited that clinical and pharmacological experiences could be related and that psychedelics might constitute a model of psychosis.[1] The discovery of lysergic acid diethylamide (LSD) in 1943 was a boon to this "model psychosis theory," spurring researchers to understand psychosis by administering psychedelics to healthy volunteers and by self-experimentation.[2,3]

The recent revival of psychedelic science generated new data and ideas, sparking great interest in the relevance of those compounds to psychosis. Do psychosis-related and drug-induced hallucinations share a similar etiology? Do they involve similar or overlapping neural mechanisms? How similar or different are these experiences phenomenologically and how are they each affected by culture?

This review from the International Consortium on Hallucinations Research (ICHR) aims to compare and contrast hallucinations under psychedelics with those observed in SCZs. Our working-group adopted a multiscale approach spanning multiple levels of understanding. First, we reviewed the underlying neural mechanisms, with a special focus on microscopic (synaptic) and macroscopic (network) mechanisms. Then, we described the subjective features of the two experiences, emphasizing their commonalities and differences and the impact of cultural factors. Finally, we described how computational models might connect these levels of analysis, from synapses to society.

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