OPEN Foundation

S. Romero

Inhibition of alpha oscillations through serotonin-2A receptor activation underlies the visual effects of ayahuasca in humans

March 25, 2016 / Ayahuasca, Neuroscience, Other subjects, Papers, Phenomenology, Psychopharmacology, Publications / By / , , , , , ,

Abstract

Ayahuasca is an Amazonian psychotropic plant tea typically obtained from two plants, Banisteriopsis caapi and Psychotria viridis. It contains the psychedelic 5-HT2A and sigma-1 agonist N,N-dimethyltryptamine (DMT) plus β-carboline alkaloids with monoamine-oxidase (MAO)-inhibiting properties. Although the psychoactive effects of ayahuasca have commonly been attributed solely to agonism at the 5-HT2A receptor, the molecular target of classical psychedelics, this has not been tested experimentally. Here we wished to study the contribution of the 5-HT2A receptor to the neurophysiological and psychological effects of ayahuasca in humans. We measured drug-induced changes in spontaneous brain oscillations and subjective effects in a double-blind randomized placebo-controlled study involving the oral administration of ayahuasca (0.75mg DMT/kg body weight) and the 5-HT2A antagonist ketanserin (40mg). Twelve healthy, experienced psychedelic users (5 females) participated in four experimental sessions in which they received the following drug combinations: placebo+placebo, placebo+ayahuasca, ketanserin+placebo and ketanserin+ayahuasca. Ayahuasca induced EEG power decreases in the delta, theta and alpha frequency bands. Current density in alpha-band oscillations in parietal and occipital cortex was inversely correlated with the intensity of visual imagery induced by ayahuasca. Pretreatment with ketanserin inhibited neurophysiological modifications, reduced the correlation between alpha and visual effects, and attenuated the intensity of the subjective experience. These findings suggest that despite the chemical complexity of ayahuasca, 5-HT2A activation plays a key role in the neurophysiological and visual effects of ayahuasca in humans.

Valle, M., Maqueda, A. E., Rabella, M., Rodríguez-Pujadas, A., Antonijoan, R. M., Romero, S., … & Feilding, A. (2016). Inhibition of alpha oscillations through serotonin-2A receptor activation underlies the visual effects of ayahuasca in humans. European Neuropsychopharmacology. http://dx.doi.org/10.1016/j.euroneuro.2016.03.012

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Serotonergic psychedelics temporarily modify information transfer in humans

March 28, 2015 / Ayahuasca, Consciousness, DMT, Neuroscience, Other subjects, Papers, Phenomenology, Psychology, Psychopharmacology, Publications / By / , , ,

Abstract

Background: Psychedelics induce intense modifications in the sensorium, the sense of “self,” and the experience of reality. Despite advances in our understanding of the molecular and cellular level mechanisms of these drugs, knowledge of their actions on global brain dynamics is still incomplete. Recent imaging studies have found changes in functional coupling between frontal and parietal brain structures, suggesting a modification in information flow between brain regions during acute effects.

Methods: here we assessed the psychedelic-induced changes in directionality of information flow during the acute effects of a psychedelic in humans. We measured modifications in connectivity of brain oscillations using transfer entropy (TE), a non-linear measure of directed functional connectivity based on information theory. Ten healthy male volunteers with prior experience with psychedelics participated in two experimental sessions. They received a placebo or a dose of ayahuasca, a psychedelic preparation containing the serotonergic 5-HT2A agonist N,N-dimethyltryptamine (DMT).

Results: the analysis showed significant changes in the coupling of brain oscillations between anterior and posterior recording sites. TE analysis showed that frontal sources decreased their influence over central, parietal and occipital sites. Conversely, sources in posterior locations increased their influence over signals measured at anterior locations. Exploratory correlations found that anterior-to-posterior TE decreases were correlated with the intensity of subjective effects, while the imbalance between anterior-to-posterior and posterior-to-anterior TE correlated with the degree of incapacitation experienced.

Conclusions: these results suggest that psychedelics induce a temporary disruption of neural hierarchies by reducing top-down control and increasing bottom-up information transfer in the human brain.

Alonso, J. F., Romero, S., Mañanas, M. À., & Riba, J. (2015). Serotonergic psychedelics temporarily modify information transfer in humans. International Journal of Neuropsychopharmacology. http://dx.doi.org/10.1093/ijnp/pyv039
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30 April - Q&A with Rick Strassman

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