The
Psychiatric University Hospital Zurich (Burghölzli) has been regarded as an influential center for research on
psychedelic substances since the discovery of
LSD in 1943 and the identification of
psilocybin in the 1960s by Swiss chemist
Albert Hofmann. From the early 1950s onward, psychedelic and non-pharmacologically induced altered states of consciousness were investigated from psychopathological, psychoanalytic, and psychometric perspectives. Since 1992, Vollenweider has continued and extended this multidisciplinary tradition by examining the molecular and neuronal circuit mechanisms underlying the psychological and therapeutic effects of classic psychedelics, dissociative anesthetics, and entactogens in humans. His work aims to clarify how, and to what extent, psychedelics and related compounds alter emotional, cognitive, and social processing, with the goal of informing the development of novel therapeutic approaches for neuropsychiatric disorders. Vollenweider's group integrates methods from psychology, cognitive neuroscience, and systems biology, employing advanced neuroimaging and brain-stimulation techniques such as
positron emission tomography (PET),
functional magnetic resonance imaging (fMRI),
electroencephalography (EEG) with event-related potentials (ERP), and
transcranial magnetic stimulation combined with EEG (TMS‑EEG). He has authored more than 200scientific papers and a monograph on the mechanisms of action of psychedelics and related psychoactive compounds. His early studies focused on the psychometric characterization of the subjective and pharmacological effects of psilocybin, LSD, the S‑ and R‑ketamine enantiomers, and
MDMA, as well as on identifying neurophysiological and neuroimaging markers with potential therapeutic relevance.
Serotonin 5-HT2A receptor and psychedelic effects His work demonstrated that the
serotonin 5-HT2A receptor is a key mediator of the
psychedelic experience, supporting a range of perceptual, emotional, and cognitive effects in humans.
Cortico-striato-thalamo-cortical (CSTC) loop model Building on neuroimaging studies and collaborative translational psychophysiological research with
Mark A. Geyer, Vollenweider formulated the cortico‑striato‑thalamo‑cortical (CSTC) loop model, a neurobiological framework for explaining the subjective effects of
psychedelics. The CSTC model proposes that psychedelics disrupt thalamo‑cortical feedback circuits that regulate bottom‑up sensory gating and top‑down cognitive control, attention, and self‑awareness. According to this model, 5-HT2A receptor activation in cortical and thalamic regions reduces thalamic filtering of sensory and interoceptive information, increasing the flow of unfiltered signals to the cortex and leading to a breakdown of hierarchical control and altered cortical network integration. Neuroimaging studies have provided empirical support for the CSTC model, reporting altered thalamo‑cortical connectivity during psychedelic states and associations with specific experiential phenomena. The model continues to be refined by Vollenweider's group and others.
Meditation and psychedelics Another line of research examines whether combining contemplative practices such as Zen or Vipassana meditation with
psychedelics may yield synergistic benefits — particularly in relation to personality development and mental health. == Awards and honors ==