Neuroimaging & Brain MeasuresDepressive DisordersAnxiety DisordersAyahuascaMescalinePsilocybin

Classical hallucinogens and neuroimaging: A systematic review of human studies: hallucinogens and neuroimaging

This systematic review (2016; s=25) analyzed neuroimaging data regarding the effects of serotonergic psychedelics, including ayahuasca, psilocybin, and LSD. The study finds that these substances generally inhibit the default mode network and modulate fronto-temporo-parieto-occipital activity, correlating with increased introspection and positive mood.

Authors

  • Jamie Hallak
  • Rafael dos Santos
  • Jaime Crippa

Published

Neuroscience and Biobehavioral Reviews
meta Study

Abstract

Serotonergic hallucinogens produce alterations of perceptions, mood, and cognition, and have anxiolytic, antidepressant, and antiaddictive properties. These drugs act as agonists of frontocortical 5-HT2A receptors, but the neural basis of their effects is not well understood. Thus, we conducted a systematic review of neuroimaging studies analyzing the effects of serotonergic hallucinogens in man. Studies published in the PubMed, Lilacs, and SciELO databases until 12 April 2016 were included using the following keywords: “ayahuasca”, “DMT”, “psilocybin”, “LSD”, “mescaline” crossed one by one with the terms “mri”, “fmri”, “pet”, “spect”, “imaging” and “neuroimaging”. Of 279 studies identified, 25 were included. Acute effects included excitation of frontolateral/frontomedial cortex, medial temporal lobe, and occipital cortex, and inhibition of the default mode network. Long-term use was associated with thinning of the posterior cingulate cortex, thickening of the anterior cingulate cortex, and decreased neocortical 5-HT2A receptor binding. Despite the high methodological heterogeneity and the small sample sizes, the results suggest that hallucinogens increase introspection and positive mood by modulating brain activity in the fronto-temporo-parieto-occipital cortex.

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Research Summary of 'Classical hallucinogens and neuroimaging: A systematic review of human studies: hallucinogens and neuroimaging'

Introduction

Serotonergic classic hallucinogens (including LSD, mescaline, psilocybin, DMT/ayahuasca) produce marked changes in perception, mood and cognition and have been reported to show anxiolytic, antidepressant and anti‑addictive effects in experimental and clinical settings. Pharmacologically, these compounds act primarily as agonists at cortical 5‑HT2A receptors and indirectly increase frontocortical glutamatergic activity, but the neural substrates mediating their subjective and therapeutic effects remain incompletely characterised. Existing human neuroimaging work has sought to map acute and longer‑term brain effects, yet before this review the authors judged that no systematic synthesis of such imaging studies had been published. Dos Santos and colleagues therefore set out to perform a systematic review of human neuroimaging studies of serotonergic hallucinogens. Rather than attempting a quantitative meta‑analysis, the investigators chose a narrative systematic approach because of heterogeneity in drugs, doses, outcome measures, secondary variables and the small number of imaging studies for some compounds; they aimed to summarise acute and non‑acute imaging findings across PET, SPECT, MRI and fMRI studies to clarify convergent neural targets and suggest directions for future research.

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Study Details

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