ADoRe study is looking for two MSc students who are interested in doing an internship or a thesis in a topic of caffeine, reinforcement learning, and adenosine-dopamine interaction. In this double-blind randomized crossover study, we will investigate 1) whether reinforcement behaviors can be augmented by acute or daily caffeine intake, and 2) if the caffeine effect on reinforcement learning is preferentially through a direct or an indirect dopaminergic pathway.