Switching and backward inhibition in major depressive disorder: the role of rumination.

Previous studies have demonstrated that individuals with major depressive disorder have difficulties switching attention from one task set to another. In the current study we examined whether ruminative thinking drives the switching deficits of depressed individuals. A secondary, more exploratory, goal of this study was to examine whether state rumination would impair depressed individuals' ability to activate a new task set, to inhibit a no longer relevant task set, or both. Participants underwent either a rumination induction or a distraction induction and then completed a backward inhibition task that measures general switching abilities and the ability to inhibit previous task sets. Although depression was not related to switching ability as a main effect, depressed individuals who were induced to ruminate exhibited poorer switching ability than did both depressed and control individuals who were distracted from ruminating and control participants who were induced to ruminate. These findings suggest that depressed individuals are characterized by switching deficits only if they are ruminating. Moreover, the finding that state rumination did not affect participants' ability to inhibit previous task sets suggests that state rumination primarily impairs noninhibitory task-switching processes. It is interesting that the opposite pattern of results was obtained for trait rumination, which was related to inhibitory deficits during switching, but not to generally poorer switching. Thus, state and trait rumination may be associated with dissociable cognitive deficits.