People with depression often have impaired cognitive function as well. They can have disturbances in concentration, memory, attention and decision-making. There is substantial evidence that these cognitive problems persist even after people's depression has improved. A study of 66 people by researchers in Germany looked into the links between depression and cognition. It found that people suffering from acute depression had problems with information processing, attention, memory and decision-making and that these problems remained in a high proportion of participants even after their depression symptoms had improved. Only decision-making improved as people's depression did. There were hardly any links between the severity of people's depression and their cognitive problems. The researchers concluded that the cognitive problems could be inherent to the participants rather than being a by-product of their depression.
Reppermund, S. ... [et al] - Cognitive impairment in unipolar depression is persistent and non-specific: further evidence for the final common pathway disorder hypothesis Psychological Medicine April 2009, 39(4), 603-614