Many of the symptoms and deficits of MDD have been hypothesized to arise from dysfunction in brain networks linking the limbic system and cortical regions [7], [11]. Disruptions in both top-down and bottom-up information processing have been observed with task-activated functional magnetic resonance imaging (fMRI), with altered functional connectivity between dorsolateral prefrontal cortex (DLPFC) and subcortical limbic structures (i.e., amygdala, thalamus) as well as subgenual anterior cingulate cortex [11]–[13]. In addition to task activation studies, resting-state fMRI has been used to examine “resting state networks” (RSNs) that subserve a range of brain processes including executive control, emotional saliency, self-referential information processing, and the default mode network (DMN) [14]–[17]. Studies of the resting state provide an important opportunity to examine connectivity unbiased by any task, and to examine the role that regions may play as parts of multiple networks. Few studies have specifically examined RSNs in MDD. Examination of the resting-state blood oxygen level-dependent (BOLD) signal in MDD shows primarily broad increases in functional connectivity in the DMN and other networks [18]–[21], although other studies have found decreased resting connectivity between some regions [22]–[24] or complex reciprocal relationships between cortical and subcortical structures [25].
