<qa>  What is the role of cholinergic neurotransmission in the behavioral and cognitive symptoms observedThe proposed inpatient or outpatient project investigates the role of cholinergic neurotransmission in the behavioral and cognitive symptoms observed in the depressed phase of both major depressive disorder MDD and bipolar disorder BD. The studies proposed here will identify anatomical correlates of the mood congruent processing bias, working memory, attention and set-shifting deficits observed in depressed subjects. Further, these studies will evaluate the effects of the cholinergic antagonist, scopolamine, both on the performance deficits and on neural activity in brain regions recruited as subjects perform these tasks. 