 We expect that mesolimbic DA mechanisms implicated in reward anticipation, reinforcement learning, and expectation play a critical role in mediating placebo responses in MDD. A better understanding of the neurobiological basis of placebo has enormous potential on different levels. On a clinical level, the understanding of placebo mechanisms could lead to a number of applications for therapeutic purposes, such as developing drugs that could enhance the effects of a therapeutic relationship or accelerate the onset of action of an antidepressant by manipulating the placebo-related mechanisms, even if the patient is hopeless or severely anhedonic. On a level of clinical trial innovation, if we confirm the role of dopamine in placebo response and we comprehend how the placebo response mechanistically takes place, this could lead to developing new drugs that could block the placebo effects in clinical trial participants and greatly decrease if not eliminate the placebo effect nested even in those subject who are drug responders, therefore increasing the effect size and decreasing the sample size of studies. Moreover if we can identify biosignatures of placebo effect and use them to predict response, we could potentially enrich samples with subjects who are less likely to be placebo responders and again this would result in increased signal detection in a clinical trial. Finally, with this initial study we plan to lay the foundation for other studies to investigate how this dopaminergic circuitry is affected by other treatments, such as psychotherapy, and what are the changes that are similar or different between antidepressants, placebo and specific forms of psychotherapy, transcranial magnetic stimulation, electroconvulsive therapy or deep brain stimulation. 