The purpose of this study is to study the relationship between insulin and glucose action and neuropsychological functioning (memory, attention, general thinking abilities) in persons with depression.

Inclusion Criteria:1)Willingness to sign the Human Subject Protection Consent Form prior to enrollment into the study.

2)Men and women ages 20 to 65 years of age. 3)Diagnosis of unipolar, non-psychotic, non-melancholic major depressive disorder (MDD) or depressive episode of bipolar disorder (Bipolar I, II or NOS), based on a Structured Clinical Interview for DSM-IV Axis I disorders (SCID) and confirmed by a psychiatrist.

4) Depression severity as defined by score of <17 on the 21-item Hamilton Rating Scale for Depression and no psychiatric admission within 6 months from study entry and no suicide attempt within the last 12 months.

5)Adequate visual and auditory acuity to allow neuropsychological testing. 6)Stable regime of psychiatric medications for 1 month prior to insulin test. Exclusion Criteria:1)Diagnosis of possible or probable cognitive impairment.

2)For women only: pregnancy, breastfeeding. 3)Personal history of Type I or Type II diabetes. 4) Unstable cardiovascular disease or other major medical condition, or history of myocardial infarction within the previous year.

5)Significant cerebrovascular disease, as evidenced by neurological examination, uncontrolled hypertension (systolic blood pressure > 170 or diastolic blood pressures > 100).

6) Current drug or alcohol abuse. 7)History of neurological disorder, e.g. multiple sclerosis, stroke etc. 8)Use of any drug that may significantly affect psychometric testing, or the insulin testing

Men and women ages 20 to 65 years of age of any ethnic background, with a diagnosis of depression, and whose depressive symptoms are currently in remission