It is a matter of size - Manipulating body size with virtual reality modulates reward sensitivity

Obesity is a major concern in clinical practice given its impact on medical and psychiatric conditions, and the pervasive social stigma it carries. Reward processing has a key role in the development and maintenance of obesity, as evidenced by reduced brain activation within the reward pathway and concurrent decrease in desire to eat following bariatric surgery. Interestingly, the experimental paradigm known as the Full Body Illusion (FBI) has been effective in impacting body size on eating attitudes. However, while both medically and experimentally induced modulation of body size modify body size perception and attitudes toward food, it remains unclear whether such illusory manipulations can affect reward-based behavior in healthy adults. To address this question, we investigated whether FBI-induced changes in body size influence reward-based learning, implicit attitudes toward food and body weight. As expected, embodying a larger avatar enhanced reward-based learning and implicit attitudes toward high-calorie foods, while reductions of the implicit weight bias occurred independently of the avatar size. This is the first study to establish a link between reward-related learning and the perception of one's body size, emphasizing a critical role for one’s own perception of their weight beyond their physical weight, in shaping approach and avoidance behavior.