Additional Study Information: This study examines normal individual differences in the ways that the body and the brain respond to emotions, and the role of mitochondria in the mind-body connection. Mitochondria are small parts of each cell that make energy to keep us alive. Participants will be asked to come for a single two full-day visit, including two nights at a hotel next to the research center (Columbia University Medical Center). The study visit will include a blood draw, a medical exam, a cognitive testing session, questionnaires, an MRI scan, and at-home collection of saliva and stool samples the following week. Participants will be paid a total of $599 plus meals and transportation.