This double-blind, within-subjects design, placebo-controlled study (n=25) found that LSD increased primary process thinking (implicit, associative, automatic, system 1) via serotonin (5HT) 2a receptor activation.
Abstract of LSD Increases Primary Process Thinking via Serotonin 2A Receptor Activation
“Rationale: Stimulation of serotonin 2A (5-HT2A) receptors by lysergic acid diethylamide (LSD) and related compounds such as psilocybin has previously been shown to increase primary process thinking – an ontologically and evolutionary early, implicit, associative, and automatic mode of thinking which is typically occurring during altered states of consciousness such as dreaming. However, it is still largely unknown whether LSD induces primary process thinking under placebo-controlled, standardized experimental conditions and whether these effects are related to subjective experience and 5-HT2A receptor activation. Therefore, this study aimed to test the hypotheses that LSD increases primary process thinking and that primary process thinking depends on 5-HT2A receptor activation and is related to subjective drug effects.
Methods: Twenty-five healthy subjects performed an audio-recorded mental imagery task 7 h after drug administration during three drug conditions: placebo, LSD (100 mcg orally) and LSD together with the 5-HT2A receptor antagonist ketanserin (40 mg orally). The main outcome variable in this study was primary index (PI), a formal measure of primary process thinking in the imagery reports. State of consciousness was evaluated using the Altered State of Consciousness (5D-ASC) rating scale.
Results: LSD, compared with placebo, significantly increased primary index (p < 0.001, Bonferroni-corrected). The LSD-induced increase in primary index was positively correlated with LSD-induced disembodiment (p < 0.05, Bonferroni-corrected), and blissful state (p < 0.05, Bonferroni-corrected) on the 5D-ASC. Both LSD-induced increases in primary index and changes in state of consciousness were fully blocked by ketanserin.
Conclusion: LSD induces primary process thinking via activation of 5-HT2A receptors and in relation to disembodiment and blissful state. Primary process thinking appears to crucially organize inner experiences during both dreams and psychedelic states of consciousness.”
Authors: Rainer Kraehenmann, Dan Pokorny, Helena Aicher, Katrin H. Preller, Thomas Pokorny, Oliver G. Bosch, Erich Seifritz & Franz X. Vollenweider
Summary of LSD Increases Primary Process Thinking via Serotonin 2A Receptor Activation
There is now accumulating evidence that supports the early meta-psychological theory of Freud that there exist two distinct modes of psychic functioning: primary process and secondary process. Primary process thinking can be operationalized and reliably assessed using formal linguistic measures.
Previous studies indicate that psychedelics activate mental processes closely related to primary process, such as vivid, dreamlike imagery, basic emotions, and bizarre thinking. Moreover, recent studies indicate that psychedelics enhance access to remote and non-obvious associations in tasks where subjects have to rely on automatic, intuitive and uncontrolled thinking.
It is still largely unknown whether LSD induces primary process thinking under placebo-controlled, standardized experimental conditions, and whether these effects are related to subjective experience and 5-HT2A receptor activation. Therefore, we performed a study to examine the relationship between primary index and other measures of psychedelic experience.
Notes on LSD Increases Primary Process Thinking via Serotonin 2A Receptor Activation
This paper is included in our ‘Top 12 Articles on Psychedelics and Serotonin (5HT) Receptors.‘
This paper uses the same participants/study as Kraehenmann and colleagues (2017), who studied the dreamlike quality of the LSD experience.
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LSD Increases Primary Process Thinking via Serotonin 2A Receptor Activation
https://doi.org/10.3389/fphar.2017.00814
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Cite this paper (APA)
Kraehenmann, R., Pokorny, D., Aicher, H., Preller, K. H., Pokorny, T., Bosch, O. G., ... & Vollenweider, F. X. (2017). LSD increases primary process thinking via serotonin 2A receptor activation. Frontiers in pharmacology, 8, 814.
Study details
Compounds studied
LSD
Topics studied
Neuroscience
Study characteristics
Original Re-analysis
Placebo-Controlled
Double-Blind
Within-Subject
Participants
25
Humans
Authors
Authors associated with this publication with profiles on Blossom
Katrin PrellerKatrin Preller is one of the upcoming researchers, currently at the University of Zurich and Yale University, and is focused on the neurobiology and pharmacology of psychedelics.
Franz Vollenweider
Franz X. Vollenweider is one of the pioneering psychedelics researchers, currently at the University of Zurich. He is also the director of the Heffter (sponsored) Research Center Zürich for Consciousness Studies (HRC-ZH).
Institutes
Institutes associated with this publication
University of ZurichWithin the Department of Psychiatry, Psychotherapy and Psychosomatics at the University of Zurich, Dr Mialn Scheidegger is leading team conducting psychedelic research and therapy development.
Compound Details
The psychedelics given at which dose and how many times
LSD 100 μg | 2xLinked Research Papers
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Dreamlike effects of LSD on waking imagery in humans depend on serotonin 2A receptor activationThis double-blind, within-subjects design, placebo-controlled study (n=25) found that LSD increased cognitive bizarreness, similar to imagery during dreaming. The effects (as usual) were blocked entirely when someone was pre-treated with ketanserin.