MDD Remission Sample: Twenty subjects (ages 18-50) male and female will be selected. Remission is defined as a period of at least three months during which the subject has not taken an antidepressant agent, with Hamilton Depression Rating Scale (HDRS; 21-item; Hamilton 1960) scores in the non-depressed range (less than 8), and with no more than one clinically significant depressive symptom.