Journal of Psychopharmacology
March 4, 2021
Tim Hirschfeld, Timo T Schmidt
90 citations
Psilocybin, the psychoactive compound in magic mushrooms, intensifies almost all characteristics of altered states of consciousness measured by standard questionnaires. A meta-analysis of data from the Altered States Database found that higher psilocybin doses correlated with stronger ratings of perceptual alterations and positively experienced ego dissolution, while measures of challenging experiences showed only small effects and were barely influenced by dose. These dose-response relationships were established in controlled laboratory experiments with healthy participants and patient groups, and may not apply to recreational use because individual and environmental factors also shape subjective experiences.
Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology
October 1, 2023
Tim Hirschfeld, Johanna Prugger, Tomislav Majić et al.
24 citations
LSD produces a sigmoid-like increase in altered states of consciousness that plateaus around 100 micrograms, with the strongest effects on perception and illusory imagination, followed by positive ego-dissolution. Anxiety and dread of ego dissolution show only small effects. Considerable variability in most measures indicates that non-pharmacological factors also shape subjective experiences. These dose-response relationships can serve as general references for future research to compare observed with expected effects and to explore phenomenological differences between psychedelics.
Current topics in behavioral neurosciences
July 31, 2024
Nathalie M Rieser, Timo T Schmidt, Katrin H Preller
5 citations
This chapter reviews current knowledge on the neural mechanisms of psychedelic drugs, focusing on human neuroimaging studies. It covers acute and subacute adverse effects and how these may inform psychiatric illness pathophysiology. The chapter examines EEG, fMRI, and PET findings, along with pre- to postdrug changes. Prevailing models discussed include the Cortico-Striato-Thalamo-Cortical feedback loop, the entropic brain hypothesis, the REBUS principle, and the claustrum hypothesis. Neural correlates of visual effects, social and emotional impacts, and ego dissolution are explored. Speculations on how acute effects relate to rare long-term adverse effects are offered, though data scarcity makes these tentative.
Network neuroscience (Cambridge, Mass.)
January 1, 2025
Ioanna A Amaya, Till Nierhaus, Timo T Schmidt
Rhythmic flicker light stimulation at 10 Hz reliably induces transient visual hallucinations in healthy people, while arrhythmic flicker does so less. Using fMRI, rhythmic flicker produced stronger activation in higher order visual cortices and selectively increased connectivity between ventroanterior thalamic nuclei and those cortices, compared to arrhythmic control. The strength of this connectivity correlated positively with the subjective intensity of hallucinations. Because the ventroanterior thalamus and higher order visual areas do not receive primary visual inputs, the findings suggest the thalamus coordinates cortical activity to generate hallucinatory experiences, offering insight into pathological hallucinations.