Additional Study Information: Are you between the ages of 18-30? Have you ever experienced unusual thoughts, experiences or feelings? Or, do you have a first-degree relative (e.g., sibling, parent, child) with schizophrenia, psychosis, or a psychotic disorder? If so, you may be eligible for a brain imaging research study that aims to understand the relationship between a chemical called dopamine and these types of thoughts. Study requirements: Physical exam, blood draw, urine sample at the Columbia University Irving Medical Center(CUIMC)/New York State Psychiatric Institute (NYSPI) 3-4 hours of interviews, one MRI scan of the brain (up to 1 hour), two PET (Positron Emission Tomography), scans on the same day, and one dose of methylphenidate. Methylphenidate is what is called a stimulant medication that can make people feel more awake, alert, and attentive. It is given for conditions such as attention deficit hyperactivity disorder and narcolepsy. As a participant, you will receive: Up to $1300, as well as reimbursement for local transportation. For further information about the study and your eligibility, please contact the Center of Prevention and Evaluation (COPE) Clinic at the New York State Psychiatric Institute at 646-774-5232.