Active clinical trials for "Anhedonia"

Major depressive disorder (MDD) is often characterized by anhedonia and impaired ability to modulate behavior as a function of rewards. However, the neurobiology of anhedonia and reduced reward responsiveness remains largely unknown. Because dopamine (DA) plays a critical role in goal-directed behavior and reinforcement learning, DA dysregulation might play an important role. In fact, several lines of evidence suggest that down-regulation of DA transmission might characterize depression vulnerability and the emergence of depressive symptoms. The current study seeks to elucidate the role of DA dysfunction in MDD. We hypothesize that MDD subjects will show reduced DAT binding potential, reduced reward learning in the probabilistic reward task, and abnormal functional magnetic resonance imaging (fMRI) activation in dorsal and ventral striatal regions during an instrumental learning task. This study will include three sessions. The first will take place at Massachusetts General Hospital or at McLean Hospital's Center for Depression, Anxiety and Stress Research. The aims of this session will be to (a) explain the study; (b) collect written informed consent, and (c) assess the subject's eligibility. Following this, another session (either second or third in order) will take place at the MGH PET Imaging Laboratory. Participants will complete a PET scan and a probabilistic reward task designed to measure reward learning and sensitivity to reward. The radioactive tracer utilized is 11C-altropane. Another session (either second or third in order) will take place at the McLean Hospital Neuroimaging Center. Participants will complete an instrumental learning task while in the fMRI, followed by a social reinforcement learning task and an implicit learning serial reaction time task upon completion of the scan. In the instrumental learning task, participants have the opportunity to earn money but need to learn, by trial and error, stimulus-outcome associations. The social reinforcement learning task is designed to investigate whether learning deficits in MDD are specific to learning from monetary incentives or whether the learning deficits are more global and are affected when learning from social rewards and punishments. Participants will also complete an implicit learning serial reaction time task, designed to exclude the possibility of global learning deficits in MDD.