Answered by Bernhard Baune
It has been suggested that a number of clinical and demographic factors are related to cognitive performance in depression. Studies have investigated whether the type of depression (unipolar, bipolar, psychotic, melancholic) contributes to cognitive deficits and it is not surprising that complex mood disorders tend to be associated with more severe cognitive deficits. For example, existing research demonstrates that bipolar disorder patients show stronger cognitive deficits compared to unipolar depressed patients.1
However, results are somewhat inconsistent among the literature, as research has also shown that cognitive deficits are similar between bipolar and unipolar depressed patients, or that differences in cognitive functioning rather relate to the profile of cognitive deficits. Among bipolar patients, patients with bipolar disorder Type I demonstrated stronger cognitive impairment than patients with bipolar disorder Type II. Along these lines, other studies have shown that patients with depression have more severe cognitive deficits compared to those with dysthymia.
The view that subtypes of depression with additional psychopathological symptoms are associated with poorer cognitive functioning is also supported by research. Specifically, poorer cognitive functioning has been reported for depressed patients with the melancholic or psychotic sub-types of depression when compared to depressed patients without these sub-type specifiers. Finally, it was found that patients with melancholic subtypes of depression not only show poorer performance but also a longer time for cognitive recovery compared to patients with non-melancholic sub-types.