Distinct Profiles of Neurocognitive Function in Unmedicated Unipolar Depression and Bipolar II Depression

Background Studies have demonstrated neuropsychological deficits across a variety of cognitive domains in depression. Few studies have directly compared depressed subjects with major depressive disorder (MDD) and bipolar disorder (BD), and many are confounded by medication status across subjects. In this study, we compared the performance of unmedicated currently depressed MDD and BD groups on a battery of neuropsychological tests that included measures of risk taking and reflection impulsivity. Methods Twenty-two MDD, seventeen BDII, and 25 healthy control subjects (HC), matched for age and IQ, were assessed on a battery of neuropsychological tests. Results The depressed groups showed comparable ratings of depression severity and age of illness onset. The MDD group was impaired on tests of spatial working memory and attentional shifting, sampled less information on a test of reflection impulsivity, and was oversensitive to loss trials on a decision-making test. The BDII subjects were generally intact and did not differ significantly from control subjects on any test. Conclusions These data indicate differing profiles of cognitive impairment in unmedicated depressed MDD versus BDII subjects. Moderately depressed BDII subjects displayed relatively intact cognitive function, whereas MDD subjects demonstrated a broader range of executive impairments. These cognitive deficits in depression were not attributable to current medication status.