Neuroimaging & Brain MeasuresMedicinal Chemistry & Drug DevelopmentAyahuasca

New World Tryptamine Hallucinogens and the Neuroscience of Ayahuasca

This book chapter (2016) provides an overview of major tryptamine-containing New World hallucinogens with a special focus on ayahuasca, for which the authors propose a model of brain effects in which ayahuasca reduces top-down constraints and facilitates bottom-up information transfer.

Authors

  • Jordi Riba

Published

Current Topics in Behavioral Neurosciences
meta Study

Abstract

New World indigenous peoples are noted for their sophisticated use of psychedelic plants in shamanic and ethnomedical practices. The use of psychedelic plant preparations among New World tribes is far more prevalent than in the Old World. Yet, although these preparations are botanically diverse, almost all are chemically similar in that their active principles are tryptamine derivatives, either DMT or related constituents. Part 1 of this paper provides an ethnopharmacological overview of the major tryptamine-containing New World hallucinogens. Part 2 focuses on ayahuasca and its effects on the human brain. Using complementary neurophysiological and neuroimaging techniques, we have identified brain areas involved in the cognitive effects induced by this complex botanical preparation. Initial SPECT data showed that ayahuasca modulated activity in higher order association areas of the brain. Increased blood perfusion was observed mainly in anterior brain regions encompassing the frontomedial and anterior cingulate cortices of the frontal lobes, and in the medial regions of the temporal lobes. On the other hand, applying spectral analysis and source location techniques to cortical electrical signals, we found changes in neuronal activity that predominated in more posterior sensory-selective areas of the brain. Now, using functional connectivity analysis of brain oscillations we have been able to reconcile these seemingly contradictory findings. By measuring transfer entropy, a metric based on information theory, we have shown that ayahuasca temporarily modifies the ordinary flow of information within the brain. We propose a model in which ayahuasca reduces top-down constraints and facilitates bottom-up information transfer. By simultaneously enhancing endogenous cortical excitability and reducing higher-order cognitive control, ayahuasca temporarily disrupts neural hierarchies allowing inner exploration and a new outlook on reality.

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Research Summary of 'New World Tryptamine Hallucinogens and the Neuroscience of Ayahuasca'

Introduction

Halberstadt and colleagues open by framing classic serotonergic hallucinogens as powerful probes of perception, cognition and consciousness. They note three major structural chemotypes that have dominated the literature — tryptamines, ergolines and phenethylamines — and stress that most modern understanding springs from molecular pharmacology that identifies serotonin 5-HT2A receptor agonism as the critical proximal mechanism. The authors emphasise that much early human work was limited, that many compounds remain pharmacologically characterised only in vitro or in animals, and that renewed clinical and neuroscientific interest in the past decades motivates a synthesis of structure–activity relationships (SAR), receptor signalling, and systems neuroscience relevant to human effects and potential therapeutic uses. The chapter sets out to: survey the chemistry and SAR of tryptamine hallucinogens (with comparisons to ergolines and phenethylamines); summarise molecular and cellular receptor pharmacology (including functional selectivity or "biased agonism"); and integrate electrophysiological, neuroimaging and behavioural data on how 5-HT2A agonists perturb cortical and thalamocortical circuitry. The introduction frames the material as an interdisciplinary review with direct relevance to clinical research and to the interpretation of experimental human studies (imaging, psychophysiology and gene-expression work).

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References (129)

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