MDMA (“ecstasy” or “molly”) is a stimulant that can produce an energizing effect and enhanced tactile experiences. It is known as a street drug of abuse, and while not FDA-approved for any indication, is also known for its therapeutic properties. Despite its recent popularity, little is known about its mode of action, subjective effects, and how its effects promote continued use. By integrating four Research Projects led by Drs. Karl Deisseroth, Lisa Giocomo, Robert Malenka, Leanne Williams, and Brian Knutson, we aim to develop a theoretically-informed characterization of the effects of these drugs on the neurobehavior of specific circuits for processing risk and reward, the connectivity of these circuits, and how these circuits and their connectivity predict acute drug experience and drug use outcomes. To do this we will administer 3 randomized doses of MDMA (80 mg, 120 mg, and placebo) while undergoing an MRI scan, cognitive assessments, and surveys assessing mood and drug effects.