Psychedelic

The purpose of this study is to evaluate a novel VRP.

The goal of this clinical trial is to learn whether certain methods of detecting awareness in vegetative or minimally conscious patients (using neuroimaging) are sensitive to the effects of psilocybin (a psychedelic drug). One of these methods includes scanning peoples' brains while they watch a film. When different individuals watch a film, their brains become synchronized with each other as they watch the plot unfold. Most importantly, if a seemingly unconscious patient also shows the same brain-synchronization, it means they might actually be conscious and aware.
To approach this goal, the investigators will be carrying out this trial in healthy volunteers. This will help better understand whether psilocybin may be a potential treatment for restoring awareness in these patients. The main questions it aims to answer are:
* Does psilocybin enhance or diminish brain synchrony during a film?
* Do changes in brain synchrony reflect differences in each individual's conscious experience?
Participants will be asked to:
* Attend two brain scanning sessions and watch a series of film clips, perform a brief mental imagery task, and listen to music - once under a placebo, and once under psilocybin.
* Play a series of games that assess their cognition (memory, reasoning, planning, etc.).
* Perform a series of visual illusions tasks.

The study hypothesis is that the antidepressant effect of psilocybin is mediated by a normalization of the functioning of the positive valence system. Depressive states, especially moderate to severe depressions that associate a certain level of anhedonia, produce an overvaluation of the cost of efforts and an infra-evaluation of the possible rewards derived from an action. Psilocybin would reduce anhedonia and the cost of efforts, facilitating the anticipation of reward. Thus, the antidepressant effect of psilocybin would be mediated by a greater anticipation of rewards (reduction of anhedonia) and a more optimistic estimation of the results of efforts (increase in motivation). Psilocybin-induced changes in the positive valence system will be observable on brain MRI images, particularly in the effort evaluation circuits: basolateral amygdala, dorsal anterior cingulate cortex, ventral pallidum, ventral striatum (VS), ventral tegmental area (VTA). The mesolimbic circuit (VS, VTA) is the anatomical substrate of anticipation of rewarding stimuli (food, sex, drugs). The amygdala also fulfills an associative function between environmental cues and rewarding stimuli. Structural and functional alterations in this circuit are associated with depressive symptoms such as anhedonia or distortions in the perception and memories of rewards. This hypothesis will be tested on a population of patients with moderate or severe depressive symptoms who meet the criteria for TRD.