Exclusion criteria included age outside the range of 18-65, substance abuse in the last month or lifetime history of substance dependence (nicotine use allowed), any neurological illness, positive pregnancy test or lactation, electroconvulsive therapy in the last 6 months, history of head trauma with loss of consciousness, and contraindications to MR scanning. The study was approved by the McLean Hospital Institutional Review Board, and all subjects gave written informed consent before participating in the study. To ensure that subjects understood the study, we conducted an informed consent survey, including simple questions about risks and benefits and the ability to withdraw consent. If the subject did not answer all questions correctly, the informed consent document was re-reviewed to ensure comprehension.
