Concerning behavioral passes, the subjects will be in front of a computer screen on which the task will be presented. For fMRI passes, the visual stimulation of the participant is done by a mirror system placed about 10 cm from the participant's eyes, allowing him to watch a translucent screen on which the visual stimuli are projected. The latter have an intensity similar to that of television images, and therefore below the maximum permitted by labor legislation. The stimuli will be projected via a video projector located at the back of the imager.

The olfactory sensitivity and the olfactory identification capacities of the subjects will be evaluated using the ETOC test. Subjects will have to define his state of hunger/satiety thanks to a questionnaire of hunger. Finally, subjects should assess the hedonic nature of the odor and the edibility of the odor source. The task to be performed will be the same for the behavioral study as for the imaging study. The subject will receive instruction from the following three: "indulge yourself", the subject must think of the desire to eat the food that will be presented to him in olfactory and visual form; "Be natural," the subject must act as naturally as possible; Or "hold back," the subject must distance themselves from their desire to eat and control themselves. In a second step, an odor will be presented for 5 seconds. This will be based on the subject's inspiration, then an image associated with the odor will be presented for two seconds.

Before and after the imaging examination, a blood sample will be taken by a medical imaging manipulator affiliated with the CERMEP whose actions will be remunerated in accordance with the usual hygiene and safety rules. The samples taken will then be annotated with the subject code and kept at the CERMEP. The volume of ghrelin sampling is 5 ml (10 ml for two samples). The volume of the leptin is 5 ml (ie 10 ml for two samples).

The proposed questionnaires respond to all ethical aspects established by international and national standards to undertake studies on human subjects. Two types of questionnaires will be used in this experiment: Inclusion of the Subjects and Exploratory Tests.

The purpose of the imaging part is to determine how high-level cognitive control (the setpoint) can affect the price of a food and the olfactory and visual perception of these foods in healthy subjects and Prader-Willi patients.

To modify the floral character of the wine used, the investigators will use the β-ionone odorant molecule (4 (2,6,6-trimethyl-1-cyclohexenyl) -3-buten-2-one (CAS number 14901-07-6) Purity ≥97.0% (Fluka) This molecule is commonly found in wines with a violet odor.

The visual stimulation of the subject will be done by a system of mirrors placed about 10 cm from the subject's eyes allows him to look at a translucent screen behind the MRI scanner and on which the visual stimuli are projected.

For each test the subjects will receive at the same time an image on the screen and a sample of wine (2 ml) delivered in the mouth of the subject thanks to the system of programmable pumps.

Sampling will be done by the subject himself by scratching and firmly pressing into the oral cavity, specifically at the cheeks and tongue for one minute, being careful not to touch the teeth and gums.

The investigators will determine how perceptual judgments are modulated by cross-modal stimuli, as well as metacognitive judgments (how individuals judge their own sensory performance). In addition, they will determine how perceptual judgments are modified in the context of group decisions and how language influences performance.