Disturbances in hedonic and motivational processes play a major role in the pathophysiology of reward-related diseases, such as obesity. To date, experimental approaches for the study of emotional and motivational processing rely on subjective assessment scales. We have therefore developed and validated a novel computer-generated test challenging visual and temporal discrimination capacities in humans. The subjects are asked to view and to compare two stimuli, an appetitive one (food pictures; F) and its devalued counterpart (food pictures in greyscale; D), at each trial, assessing either the size (task A) or the duration of presentation (task B). Geometric figures are used as controls and presented in color (C) or greyscale (D). Both tasks are registered under the French agency for the protection of computer software. Here, we propose to use our novel test to: i) assess the hedonic and motivational state in subjects suffering from obesity, ii) compare their responses with healthy volunteers, and iii) establish relationships with biological markers known to be highly involved in the regulation of both emotional and motivational processes, such as endocannabinoids. Responses to the test in obese patients will be evaluated during two separate experimental sessions under either fasting or satiety conditions.

The present study is expected to begin mid-November 2013 for a total duration of 24 consecutive months. A sample of 25 patients suffering from obesity will be recruited and compared with 25 healthy normal volunteers who are free from any previous or current metabolic and psychiatric disorders. They will be matched on age and sex. They will be screened using the "Association pour la Méthodologie et la Documentation en Psychiatrie" questionnaire for obtaining a series of information, comprising the marital status, number of children, number of siblings, education and training, professional qualifications, significant life events... They will be evaluated with the Mini-International Neuropsychiatric Interview in order to determine the presence of mood disorders and associated psychopathology. The Three-Factor Eating Questionnaire will be employed for measuring three separate aspects of eating behavior: cognitive restraint, uncontrolled eating, and emotional eating. This will be completed with the Multidimensional Body Self-Relations Questionnaire and the State-Trait Anxiety Inventory in order to assess the body satisfaction and anxiety levels, respectively. Beyond all these assessments, two separate experimental sessions will be conducted, one in satiety and the other in fasting. During each session, the participants will be asked to perform the two validated instrumental tasks in front the screen of a computer. Plasma levels of endocannabinoids will be monitered by collecting blood samples prior to the consumption of a calorically-defined meal and while carrying out the computer-generated tasks under satiety. Blood will be withdrawn at the same time-points during the session in fasting. Visual analogue scales (VAS) assessing hunger levels will be completed before blood is collected. A VAS will be also used for the global assessment of appetitive properties of the viewed food images just before the end of the second experimental session.