Major Depressive Disorder (MDD) is characterized by dysphoric and anxious mood, difficulties in concentration and decision making, ruminative and self-referential thinking, as well as anhedonia and lack of motivation [1], [2]. These symptoms are consistent with deficits seen in experimental paradigms, in which patients with MDD show deficits in emotional and cognitive information processing [3], [4]. Aberrant emotional processing has been demonstrated in the context of reactions to emotional facial expression or startle in the context of pleasant stimuli [5], [6]. Cognitive deficits have been reported in memory processing, learning, attention, and executive function [7], [8]. While clusters of these symptoms are used to define MDD, their neurobiological origins are not well understood [9]. Elucidating the linkage between the symptoms and pathophysiology of MDD could lead to more accurate and meaningful diagnoses that would have greater prognostic significance [10].
