The purpose of the study is to learn how differences in learning under mildly-stressful circumstances may be changed by taking an antidepressant medication. This medication is called Lexapro (Escitalopram). The investigators will also examine the impact of any anxiety, depression, and stress related symptoms on learning processes. The investigators will also look at the response of these symptoms to Lexapro.

Inclusion Criteria:

1. Male or female outpatients 18 to 75 years of age
2. Must have no current DSM-IV Axis I diagnosis as measured by the SCID (Structured Clinical Interview for DSM-IV-TR axis 1 disorders) with a trained study investigator. Past history of anxiety disorders, major depressive episodes or substance abuse disorders at least six months prior to baseline are not exclusionary.

Exclusion Criteria:

1. Patients will be excluded from entry into the study for current serious medical conditions or other conditions deemed likely to result in surgery or hospitalization.
2. Patients with a history of trauma resulting in head injury related seizures, or with epilepsy (except a prior history of febrile seizures of infancy which are not exclusionary).
3. Pregnant or lactating women or those of childbearing potential not using medically accepted forms of contraception will be excluded.
4. Concurrent use of other antidepressants, benzodiazepines or antipsychotic medications.
5. Patients with a history of hypersensitivity to escitalopram are excluded.
6. Individuals must have discontinued MAO inhibitors more than 14 days before starting study drug.
7. Additional contraindicated drugs during the study are pimozide, furazolidine, isocarboxazid, lazabemide, and St. John's Wort.
8. Participants meeting DSM-IV or SCID criteria for a substance use disorder in the last six months other than nicotine dependence and those with a positive toxicology screen at baseline consistent with evidence of current substance abuse or dependence as determined by clinical interview.
9. A lifetime history of Bipolar or any psychotic disorder is excluded.
10. Current claustrophobia is exclusionary.
11. Patients currently taking any narcotic will be excluded.

AEs were assessed in the period following randomization/medication initiation, through the experimental portion of the study (14-17 days post medication initiation), and 7 days following medication discontinuation.

AEs were defined as any untoward or unfavorable medical occurrence in a human subject. SAEs event were defined as any event temporally associated with the subject's participation that: results in death, is life-threatening, results in inpatient hospitalization, results in significant disability, or results in a congenital anomaly or birth defect