Testing the cognitive effort hypothesis of cognitive impairment in major depression

Background: It is widely accepted that depression is associated with deficits in a range of cognitive domains. However, there is no consensus regarding the neuropsychological profile in depression. Aim: The aim of the present report is to test the cognitive effort hypothesis as a possible framework for understanding the observed cognitive impairment in major depressive disorder (MDD), using the Delis Kaplan Executive Function system (D-KEFS). Method: Twenty-four patients with recurrent MDD, in the acute phase of illness, were compared with a healthy control group. We expected that the patient group would show impairment on tests that measure higher-level effortful cognitive processing, whereas basic cognitive skills would be equal to the control group. Results: There were no differences between the two groups on measures of basic cognitive skills, except for Colour Naming. Furthermore, MDD patients performed significantly worse than the control group on three out of seven of the cognitively effortful measures; namely Inhibition, Inhibition/Switching and Category Fluency. Conclusions: We could not find consistent support for the cognitive effort hypothesis in the present study. However, the results indicate that depressed patients have a specific impairment within the Executive Function domain affecting Inhibition, Inhibition/Switching and Category Fluency.