Additional Study Information: Note: Due to COVID-19, all the research procedures, except the phone screening for this study, has been on pause. The in-person screening and the research procedures will start after the pause is lifted. The purpose of this study is to examine the use of a new portable brain imaging device to study a measure of brain activity, and to develop optimal methods for analyzing the data from this device. After baseline assessments including clinical interview, physical exam, and blood tests, participants will undergo 3 brain scans on separate days: two Positron Emission Tomography (PET) scans, each lasting one hour, using different PET cameras, to measure metabolic activity in the brain, and one Magnetic Resonance Imaging (MRI) scan, to obtain information about brain structure. Participants will be compensated $250 for each of the PET scans, a $100 for the MRI scan, and $100 bonus for completing all the research procedures, so the total compensation is up to $700.