Cognitive ‘branching’ processes in major depression: evidence for a generalised learning deficit

Background: Patients with depression demonstrate cognitive impairment on a wide range of cognitive tasks, particularly putative tasks of frontal lobe function. We wanted to investigate the possibility that patients are impaired at cognitive ‘branching’, a process requiring holding in mind one goal while performing sub-goal processes. This task has been previously demonstrated to activate anterior (BA10) prefrontal regions of the brain. Methods: 11 non-medicated patients with major depression were compared to 11 matched controls in a behavioural study on a task of cognitive ‘branching’. In the version employed here, we recorded participant’s performance as they learnt to perform the task. This involved participants completing a control condition, followed by a working memory condition, a dual-task condition and finally the branching condition, which integrates processes in the working memory and dual-task conditions. We also measured participants on a number of other cognitive tasks as well as mood-state before and after the branching experiment. Results: Patients took longer to learn the first condition, but performed comparably to controls after six runs of the task. Overall, reaction times decreased with repeated exposure on the task conditions in controls, with this effect attenuated in patients. Importantly, no differences were found between patients and controls on the branching condition. There was, however, a significant change in mood-state with patients increasing in positive affect and decreasing in negative affect after the experiment.