Translational Psychiatry
July 15, 2026
Annette Johansen, Pontus Plavén-sigray, Martin K Madsen et al.
Psychedelics such as psilocybin have been linked to enhanced neuroplasticity and symptom relief in affective disorders, but the neurobiological mechanisms and impact of environmental context remain unclear. Here, we tested whether a single dose of psilocybin (0.3 mg/kg) alters synaptic density in healthy individuals and whether setting-dependent subjective experience shapes this effect. Fifteen...
Nature Communications
June 24, 2026
Drummond E-Wen Mcculloch, Anders S. Olsen, Brice Ozenne et al.
A prominent theory of psychedelics is that they increase brain entropy. Thirteen studies have evaluated psychedelic effects on fMRI brain entropy, each applying a distinct measure. Here we evaluated these metrics in an independent 28-participant healthy cohort with 121 pre- and post-psilocybin fMRI scans. We assessed relations between brain entropy and objective and subjective psychedelic drug...
Journal of psychopharmacology (Oxford, England)
May 29, 2026
Kristoffer Brendstrup‐brix, Brice Ozenne, Patrick M. Fisher et al.
Patients with chronic cluster headache (CCH) suffer from poor sleep, which may impact their brain microstructure and parenchymal clearance of waste products. Psilocybin has shown promise for the treatment of CCH and has been linked to increased neuroplasticity with possible influences on brain microstructure. To investigate the effects of psilocybin on sleep, brain water diffusivity, and...
bioRxiv
April 13, 2026
Anders S. Olsen, Kristian Larsen, Drummond E. Mcculloch et al.
Abstract Psilocybin and other serotonergic drugs acutely alter human brain function and large-scale connectivity as measured with BOLD fMRI, but whether these effects are frequency-specific remains unknown. We applied multitaper spectral and cross-spectral analyses to resting-state fMRI data from 28 healthy volunteers scanned multiple times acutely following oral psilocybin administration (0.2...
medRxiv
January 16, 2026
Kristian Larsen, Patrick M. Fisher, Drummond E. Mcculloch et al.
1 citation
Classical psychedelics have regained interest for their potential to treat psychiatric and neurological disorders, and explore neural mechanisms supporting perception, cognition, and mood. Acute psychedelic effects have been linked to increases in brain complexity and entropy, but it is unclear if these changes are specific to psychedelics or reflect more general psychoactive effects. Here, we...
Research Square
October 10, 2025
Gitte M. Knudsen, Annette Johansen, Pontus Plavén-sigray et al.
Abstract Psychedelics such as psilocybin have been linked to enhanced neuroplasticity and symptom relief in affective disorders, but the neurobiological mechanisms and impact of environmen-tal context remain unclear. Here, we tested whether a single dose of psilocybin alters synap-tic density in healthy individuals and whether setting-dependent subjective experience shapes this effect. Fifteen...
Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism
February 26, 2025
Kristian Larsen, Ulrich Lindberg, Brice Ozenne et al.
9 citations
Psilocin, the active metabolite of psilocybin, is a psychedelic and agonist at the serotonin 2A receptor (5-HT2AR) that has shown positive therapeutic effects for brain disorders such as depression. To elucidate the brain effects of psilocybin, we directly compared the acute effects of 5-HT2AR agonist (psilocybin) and antagonist (ketanserin) on cerebral blood flow (CBF) using pseudo-continuous...
The British Journal of Psychiatry
December 5, 2024
Emma S Høgsted, Vincent Beliveau, Brice Ozenne et al.
4 citations
Background Using [ 18 F]altanserin, a serotonin 2A receptor (5-HT 2A R) antagonist Positron Emission Tomography (PET) tracer, a positive association between cortical 5-HT 2A R binding and the inward-directed facets of neuroticism has been demonstrated in healthy individuals. Psilocybin, a 5-HT 2A R agonist, shows promise for the treatment of depression, reducing neuroticism and mood symptoms...
Neuroscience Applied
December 30, 2023
Sophia Armand, Kristian Larsen, Martin K Madsen et al.
7 citations
The serotonergic psychedelic psilocybin acutely induces changes in emotional states. However, it remains unresolved whether psilocybin acutely modulates amygdala reactivity to emotions, a brain region critically involved in emotion processing. Using functional magnetic resonance imaging (fMRI), we examined in 26 healthy individuals whether amygdala responses to angry, fearful and neutral faces...
medRxiv
July 3, 2023
Drummond E-Wen Mcculloch, Anders S. Olsen, Brice Ozenne et al.
20 citations
preprint
A prominent theory of psychedelics is that they increase brain entropy. Twelve studies have evaluated psychedelic effects on fMRI brain entropy quantifications, no findings have been replicated. Here we evaluated these metrics in an independent 28-participant healthy cohort with 121 pre- and post-psilocybin fMRI scans. We assessed relations between brain entropy and plasma psilocin, brain...
Neuroimage
October 27, 2022
Anders Lykkebo-Valløe, Brice Ozenne, Sophia Armand et al.
44 citations
Our findings suggest that the acute perceptual psychedelic effects induced by psilocybin may stem from drug-level associated decreases in the occurrence and duration of lateral and medial frontoparietal connectivity motifs. We apply and argue for a modified approach to modeling eigenvectors produced by LEiDA that more fully acknowledges their underlying structure. Together these findings...
Frontiers in Psychology
October 5, 2022
Anna Søndergaard, Brice Ozenne, Sophia Armand et al.
35 citations
Background Psilocybin-induced mystical-type experiences are associated with lasting positive psychological outcomes. Recent studies indicate that trait mindfulness is increased 3 months after psilocybin intake, preceded by decreases in neocortical serotonin 2A receptor (5-HT 2A R) binding. However, the association between psilocybin-induced mystical-type experiences and subsequent changes in...
Frontiers in Pharmacology
March 9, 2022
Drummond E-Wen Mcculloch, Maria Zofia Grzywacz, Martin Bruun Madsen et al.
91 citations
Psychedelic drugs such as psilocybin have shown substantial promise for the treatment of several psychiatric conditions including mood and addictive disorders. They also have the remarkable property of producing persisting positive psychological changes in healthy volunteers for at least several months. In this study (NCT03289949), 35 medium-high doses of psilocybin were administered to 28...
medRxiv
December 17, 2021
Anders S. Olsen, Anders Lykkebo-Valløe, Brice Ozenne et al.
4 citations
preprint
Abstract Background Psilocin, the neuroactive metabolite of psilocybin, is a serotonergic psychedelic that induces an acute altered state of consciousness, evokes lasting changes in mood and personality in healthy individuals, and has potential as an antidepressant treatment. Examining the acute effects of psilocin on resting-state dynamic functional connectivity implicates network-level...
December 14, 2021
Drummond E-Wen Mcculloch, Maria Zofia Grzywacz, M. Madsen et al.
2 citations
preprint
Psychedelic drugs such as psilocybin are under investigation for the treatment of several psychiatric conditions. They also have the remarkable property of producing persisting positive psychological changes in healthy volunteers for at least several months. In this study, 35 medium-high doses of psilocybin were administered to 28 healthy volunteers (12 females). By the end of the dosing day,...
European neuropsychopharmacology : the journal of the European College of Neuropsychopharmacology
September 1, 2021
Martin K Madsen, Dea S Stenbæk, Albin Arvidsson et al.
132 citations
The emerging novel therapeutic psilocybin produces psychedelic effects via engagement of cerebral serotonergic targets by psilocin (active metabolite). The serotonin 2A receptor critically mediates these effects by altering distributed neural processes that manifest as increased entropy, reduced functional connectivity (FC) within discrete brain networks (i.e., reduced integrity) and increased...
Journal of Psychopharmacology
June 30, 2021
Drummond E-Wen Mcculloch, Martin Bruun Madsen, Dea Siggaard Stenbæk et al.
79 citations
Background: Psilocybin is a psychedelic drug that has shown lasting positive effects on clinical symptoms and self-reported well-being following a single dose. There has been little research into the long-term effects of psilocybin on brain connectivity in humans. Aim: Evaluate changes in resting-state functional connectivity (RSFC) at 1 week and 3 months after one psilocybin dose in 10 healthy...
Social Cognitive and Affective Neuroscience
April 23, 2021
Maja Rou Marstrand-Joergensen, M. Madsen, Dea Siggaard Stenbæk et al.
20 citations
Evaluating associations between the five-factor personality domains and resting-state functional connectivity networks (e.g. default mode network, DMN) highlights distributed neurobiological systems linked to behaviorally relevant phenotypes. Establishing these associations can highlight a potential underlying role for these neural pathways in related clinical illness and treatment response....
International Journal of Molecular Sciences
January 15, 2021
Nakul Ravi Raval, Annette Johansen, Lene Lundgaard Donovan et al.
191 citations
A single dose of psilocybin, a psychedelic and serotonin 2A receptor (5-HT2AR) agonist, may be associated with antidepressant effects. The mechanism behind its antidepressive action is unknown but could be linked to increased synaptogenesis and down-regulation of cerebral 5-HT2AR. Here, we investigate if a single psychedelic dose of psilocybin changes synaptic vesicle protein 2A (SV2A) and...
European Neuropsychopharmacology
December 4, 2020
Lene Lundgaard Donovan, Jens Vilstrup Johansen, Nídia Fernandez Ros et al.
45 citations
Psilocybin has in some studies shown promise as treatment of major depressive disorder and psilocybin therapy was in 2019 twice designated as breakthrough therapy by the U.S. Food and Drug Administration (FDA). A very particular feature is that ingestion of just a single dose of psilocybin is associated with lasting changes in personality and mood. The underlying molecular mechanism behind its...
Journal of Psychopharmacology
October 8, 2020
Dea Siggaard Stenbæk, M. Madsen, Brice Ozenne et al.
81 citations
Background: Psilocybin is a serotonergic psychedelic with psychoactive effects mediated by serotonin 2A receptor (5-HT2AR) activation. It produces an acute psychedelic altered state of consciousness with a unique phenomenology that can be temporally characterized by three intensity phases: onset of psychoactive effect, a peak plateau and return to normal consciousness. Aims: We evaluated...
European Neuropsychopharmacology
March 4, 2020
M. Madsen, Patrick M. Fisher, Dea Siggaard Stenbæk et al.
189 citations
A single dose of the serotonin 2A receptor (5-HT2AR) agonist psilocybin can have long-lasting beneficial effects on mood, personality, and potentially on mindfulness, but underlying mechanisms are unknown. Here, we for the first time conduct a study that assesses psilocybin effects on cerebral 5-HT2AR binding with [11C]Cimbi-36 positron emission tomography (PET) imaging and on personality and...
Neuropsychopharmacology
March 8, 2019
M. Madsen, Patrick M. Fisher, Daniel Burmester et al.
21 citations
correction
The original version of this article contained an error in the labelling of Figures 2 and 3. While the captions and figures themselves are correct, in order to correspond with the in-text references, they have now been re-numbered in both the PDF and HTML versions of the article.
Neuropsychopharmacology
January 26, 2019
M. Madsen, Patrick M. Fisher, Daniel Burmester et al.
505 citations
The main psychedelic component of magic mushrooms is psilocybin, which shows promise as a treatment for depression and other mental disorders. Psychedelic effects are believed to emerge through stimulation of serotonin 2A receptors (5-HT2ARs) by psilocybin's active metabolite, psilocin. We here report for the first time the relationship between intensity of psychedelic effects, cerebral 5-HT2AR...