Inclusion Criteria:

• WEIGHT: less than or at 20% over ideal weight, as specified in the 1983 Metropolitan Height and Weight Tables. Patients who deviate from these ranges may be reviewed on an individual basis by the Investigator. This criterion is necessary because of mechanical limitations in fitting overweight individuals into the scanner, and the risk of excessive claustrophobic responses if tightly constricted.
• HEALTH: healthy, ambulatory normal or depressed adults

Exclusion Criteria:

• Presence of aneurysm clips, cardiac pacemakers, cochlear implants, metal in the eyes, and implanted insulin pumps.
• Evidence of significant hepatic, gastrointestinal, renal, respiratory, endocrine, hematologic, neurologic, psychiatric, or cardiovascular system abnormalities.
• Pregnancy.
• Patients with a known or suspected history of alcohol or drug misuse and/or a positive urine drug screen.
• Patients who are unwilling or unable to abide by the requirements of the study or who violate the prohibitions and restrictions of the study.
• Any condition which would make the patient, in the opinion of the Investigator, unsuitable for the study.
• Patients on antidepressants may not be taking any other medication, except at the discretion of the investigator. Untreated depressed or healthy subjects must be free of all medications except as approved by the investigator.
• Patients with serious medical illness, history or signs/symptoms of lumbar spine/disc disease or significant laboratory findings.
• Patients who present significant suicide risk, e.g. with a history of highly impulsive suicide attempts.