Bipolar disorder is a serious psychiatric illness thought to involve deficits in the neural substrates for emotion regulation because of its characteristic profile of lifetime depressed and manic mood episodes (1, 2). Neuroimaging research in healthy subjects has revealed a number of brain areas involved in emotional regulation, including subcortical (e.g., amygdala) and ventrolateral prefrontal cortical (vlPFC) regions (3, 4). Research in both humans and primates has additionally demonstrated strong anatomical projections between these areas, forming the substrate for which functional coupling (connectivity) is possible (5, 6). The amygdala, for example, is functionally responsive to emotional stimuli, while the vlPFC is instrumental in the regulation of that response. In healthy subjects, during down-regulation of emotion, the functional connectivity between these areas has been observed to increase (7, 8). The above-referenced functional magnetic resonance imaging (fMRI) studies of emotion regulation involve observation of brain activity while subjects perform a task. Recent studies that have evaluated subjects while not performing any cognitive tasks–e.g., resting state studies–have also revealed intrinsic activation patterns in the brain. Resting state fMRI provides complementary information to task-based fMRI in that both provide a platform for examining functional brain networks. Spatially distributed large-scale brain networks can be reliably derived and interrogated by either kind of fMRI experiment (9–11) and one could argue that both contribute different dimensions to a full characterization of brain activity. A variety of methods have been used to analyze such data (12) and have been applied to diverse clinical populations in the effort to delineate disease-related dysfunctions in connectivity (13). While there are a handful of studies that have investigated functional connectivity in bipolar disorder, few are resting state studies (Table 1). Of these, there is some overlap with the regions used as seeds, such as the medial prefrontal cortex (14, 15) or amygdala (16, 17) but the findings show differences in connectivity in lateralization (left or right hemisphere), sign (positive or negative coupling), and between-group differences (healthy subjects > bipolar disorder or bipolar disorder > healthy subjects). Three of these studies investigated bipolar mania and/or depression (14, 15, 17); however, one combined several mood states into its bipolar disorder sample (16) while another combined bipolar I and II disorder subjects (14). This latter issue is particularly problematic as there is evidence to suggest that patterns of activation and connectivity change with different mood state and subtype of bipolar disorder (17–19). For a clearer picture of the underlying pathophysiology of bipolar disorder, further research that investigates common regions in both hemispheres in single mood states and in single bipolar disorder subtypes is necessary. Table 1 A selection of functional magnetic resonance imaging (fMRI)connectivity studies in bipolar disorder The goal of the present resting state study was to elucidate differences in intrinsic functional connectivity that might contribute to mood lability in bipolar I disorder. We therefore took a focused approach to assessing connectivity in two bilateral brain regions strongly implicated in emotion regulation (four regions in total: right and left amygdalae and right and left vlPFC) in a group of euthymic bipolar I disorder subjects. We hypothesized that subjects with bipolar I disorder would demonstrate aberrant functional connectivity relative to healthy subjects between amygdalae and lateral vlPFC–regions that subserve emotion regulation. Furthermore, observed alterations of brain connectivity during the euthymic state may be considered a potential biomarker of trait aspects of the disease.