Impaired sustained attention and executive dysfunction: bipolar disorder versus depression-specific markers of affective disorders

Objective - To identify neurocognitive measures that could be used as objective markers of bipolar disorder.
Methods - We examined executive function, sustained attention and short-term memory as neurocognitive domains in 18 participants with bipolar disorder in euthymic state (Beuth), 14 in depressed state (Bdep), 20 with unipolar depression (Udep) and 28 healthy control participants (HC). We conducted four-group comparisons followed by relevant post hoc analyses.
Results - Udep and Bdep, but not Beuth showed impaired executive function (p = 0.045 and p = 0.046, respectively). Both Bdep and Beuth, but not Udep, showed impaired sustained attention (p = 0.001 and p = 0.045, respectively). The four groups did not differ significantly on short-term memory. Impaired sustained attention and executive dysfunction were not associated with depression severity, duration of illness and age of illness onset. Only a small number of abnormal neurocognitive measures were associated with medication in Bdep and Beuth.
Conclusion - Impaired sustained attention appears specific to bipolar disorder and present in both Beuth and Bdep; it may represent an objective marker of bipolar disorder. Executive dysfunction by contrast, appears to be present in Udep and Bdep and likely represents a marker of depression.