Abstract
Bipolar disorder is characterized by a functional imbalance between hyperactive ventral/limbic areas and hypoactive dorsal/cognitive brain regions potentially contributing to affective and cognitive symptoms. Resting-state studies in bipolar disorder have identified abnormal functional connectivity between these brain regions. However, most of these studies used a seed-based approach, thus restricting the number of regions that were analyzed. Using data-driven approaches, researchers identified resting state networks whose spatial maps overlap with frontolimbic areas such as the default mode network, the frontoparietal networks, the salient network, and the meso/paralimbic network. These networks are specifically engaged during affective and cognitive tasks and preliminary evidence suggests that functional connectivity within and between some of these networks is impaired in bipolar disorder. The present study used independent component analysis and functional network connectivity approaches to investigate functional connectivity within and between these resting state networks in bipolar disorder. We compared 30 euthymic bipolar I disorder patients and 35 age- and gender-matched healthy controls. Inter-network connectivity analysis revealed increased functional connectivity between the meso/paralimbic and the right frontoparietal network in bipolar disorder. This abnormal connectivity pattern did not correlate with variables related to the clinical course of the disease. The present finding may reflect abnormal integration of affective and cognitive information in ventral-emotional and dorsal-cognitive networks in euthymic bipolar patients. Furthermore, the results provide novel insights into the role of the meso/paralimbic network in bipolar disorder.
Highlights
Bipolar disorder (BD) is a heterogeneous disease characterized by acute dysfunctional mood states, alternating between mania (BD-I) or hypomania (BD-II) and depression, and related to dysfunctional emotion generation and regulation [1]
We focused on the default mode network (DMN), the frontoparietal networks (FPNs), the salient network (SN), and the meso/paralimbic network (MPN) as these networks or brain regions within these networks have been previously implicated in BD [5,22,23,34,36,37]
The present study extends previous knowledge by investigating functional connectivity within and between resting state networks (RSNs) that have not been examined in detail despite their potential relevance for both affective and cognitive dysfunctions in BD
Summary
Bipolar disorder (BD) is a heterogeneous disease characterized by acute dysfunctional mood states, alternating between mania (BD-I) or hypomania (BD-II) and depression, and related to dysfunctional emotion generation and regulation [1]. It has been proposed that the neural mechanisms underlying dysfunctional emotion regulation as well as cognitive impairments in BD are related to hypoactive ventral prefrontal areas that exert diminished top-down control on limbic brain structures resulting in hyperactivity of these structures [1,4,5,6,7] This disturbed frontolimbic functional connectivity (FC) has been shown during cognitive tasks [8], emotional tasks [9,10,11], and during resting state [12,13,14,15,16] in both symptomatic and euthymic BD patients. ICA takes into account the BOLD signal from the whole brain to generate functional maps of different brain networks [17]
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