Psilocybin’s effect on human brain synaptic plasticity

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 healthy participants had a psilocybin-induced psychedelic experi-ence either inside an MRI scanner or in a therapeutic-like room. We assessed synaptic densi-ty changes by measuring the Synaptic Vesicle glycoprotein 2A in the frontal cortex and hip-pocampus with [¹¹C]UCB-J PET at baseline and one-week post-dose, and assessed subjective experiences immediately afterwards and at three months. Participants treated in the thera-peutic-like setting exhibited more intense mystical-type experiences, longer-lasting psycho-logical benefits, and greater increases in synaptic density than those dosed in the MRI scan-ner. These findings indicate that psilocybin’s neuroplastic effects are modulated by envi-ronmental context, with important implications for psychedelic-assisted therapies.