Healthy brains scanned twice to test reliability of imaging methods

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

* INCLUSION CRITERIA: All Participants: * Older than 18 years of age. * Ability to provide written informed consent as determined by physical examination and verbal communication. Capacity to consent will be determined by those obtaining the informed consent EXCLUSION CRITERIA: * Pregnant or breast feeding. Females of childbearing potential must have negative urine pregnancy test and not be currently breastfeeding. Post-menopausal or surgically sterile (tubal ligation or hysterectomy) females satisfy these criteria. * The following current chronically used (within 2 months of study procedures) psychoactive medications or medications that can affect brain function (including but not limited to meperidine, tricyclic antidpressants, selective serotonin reuptake inhibitors (SSRIs), or serotonin norepinephrine reuptake inhibitors (SNRIs), stimulant or stimulant-like medications (amphetamine, methylphenidate, modafinil); opioid analgesics; antianginal agents; antiarrhythmics; systemic corticosteroids; anticholinergics; anticoagulants; anticonvulsants; antihistamines (sedating); beta blocker antihypertensives; antineoplastics; antiobesity; antipsychotics; anxiolytics (benzodiazepine or barbiturates); lithium; muscle relaxants, and systemic steroids as determined by history and clinical exam. * Current or past DSM-IV or DSM-5 diagnosis of a psychiatric disorder as determined by history and clinical exam including substance use disorder (except for nicotine/caffeine), alcoholism and alcohol dependence. Past history of a mental disorder as defined by DSM-IV or DSM-5 will be excluded only if it required hospitalization (any length), or chronic medication management (more than 4 weeks), and that could impact brain function at the time of the study. * Those with a binge drinking history every month continuously for the last 10 years will also be excluded. Binge drinkers are those who being female consume 4 or more drinks and males consume 5 or more drinks in one occasion at least once a month. * Major medical problems that can impact brain function at the time of the scan (including but not limited to HIV; central nervous system including seizures and psychosis; cardiovascular including hypertension and arrhythmias; metabolic, autoimmune, endocrine) as determined by history and clinical exam. Participants aged 60 and older with any medical problems that are controlled will not be excluded. * Any clinically significant laboratory finding as determined during the screening procedures. * Have had previous radiation exposure (from X-rays, PET scans, or other exposure) that, with the exposure from this study, would exceed NIH annual research limits. * Head trauma with loss of consciousness for more than 30 minutes. * Presence of ferromagnetic objects in the body that are contraindicated for MRI/MRS of the head (pacemakers or other implanted electrical devices, brain stimulators, some types of dental implants, aneurysm clips, metallic prostheses, permanent eyeliner, implanted delivery pump, or shrapnel fragments), fear of enclosed spaces, or other standard contraindication to MRI/MRS (self-report checklist). * Cannot lie comfortably flat on back for up to 2 hours in the PET and MRI/MRS scanners. * Body weight \> 250 kg. This is the upper limit that the bed of the MR scanner can accommodate. * NIH employees who are study investigators, as well as their superiors, subordinates and immediate family members (adult children, spouses, parents, siblings). * Non-English speakers (subjects must be able to read and comprehend English). * Subjects will not be excluded from enrollment onto this study if their urine test is positive for drugs. However, if they test positive on scheduled study procedure days involving study imaging (MRI/MRS and PET) and Neuropsychological testing, the procedures will be postponed and rescheduled. We will allow for up to 3 rescheduled study days that were the result of positive urine drug screens. If the drug test is positive on the third rescheduled visit, the participant will be withdrawn from the study. The intent of the research has no prospect of direct benefit to the subject. Therefore, we are excluding non-English speakers in this research study since it includes the administration of questionnaires, surveys and assessments that are validated for English, although some are available in Spanish.