Although manic episodes reportedly contribute to cognitive deficits in bipolar I disorder, the contribution of depressive episodes is poorly researched.

We investigated the impact of depressive episodes on cognitive function early in the course of bipolar I disorder.

A total of 68 patients and 38 controls from the Systematic Treatment Optimization Programme for Early Mania (STOP-EM) first-episode mania programme were examined. We conducted (a) a cross-sectional analysis of the impact of prior depressive episodes on baseline cognitive function and (b) a prospective analysis assessing the contribution of depression recurrence within 1 year following a first episode of mania on cognitive functioning.

The cross-sectional analysis showed no significant differences between patients with past depressive episodes compared with those without, on overall or individual domains of cognitive function (all P>0.09). The prospective analysis failed to reveal a significant group×time interaction for cognitive decline from baseline to 1 year (P = 0.99) in patients with a recurrence of depressive episodes compared with those with no recurrence. However, impaired verbal memory at baseline was associated with a depression recurrence within 1 year.

Although deficits in all domains of cognitive function are seen in patients early in the course of bipolar disorder, depressive episodes do not confer additional burden on cognitive function. However, poorer verbal memory may serve as a marker for increased susceptibility to depression recurrence early in the course of illness.