Increased neural resources recruitment in the intrinsic organization in major depression.

OBJECTIVE To investigate the functional connectivity (FC) pattern within an intrinsic functional organization, including both task-positive (TPN) and task-negative (TNN) networks, in major depressive disorder (MDD), and to examine relationships between the involved FCs and clinical variables. METHODS Resting-state FC analyses were used to identify the component brain regions of the intrinsic organization and to investigate the FCs of the individual component regions in 18 first-episode, medication-naïve MDD and 20 healthy control subjects. RESULTS We found that the intrinsic organization of the depressed group recruited more extensive regions than the control group. All of the altered FCs associated with the component regions increased in MDD. Specifically, in the TPN the increased FCs were primarily located in the bilateral lateral prefrontal cortices and the inferior parietal lobes, which have been implicated in attention and adaptive control. In the TNN, the increased FCs were primarily located in the posterior cingulate cortex and the medial orbitofrontal cortex, which are involved in episodic memory, self-reflection and emotional regulation. We also found increased anti-correlations between the two networks. Additionally, the strengths of the FCs associated with the lateral prefrontal cortices were found to be correlated with the duration of the depressive episode and the HDRS scores in the depressed patients. LIMITATIONS Clinical correlates of these abnormal FCs should be cautiously interpreted due to the small sample size in this study. CONCLUSIONS Abnormalities in the intrinsic organization may be an underlying basis for the pronounced and prolonged negative bias in processing emotional information observed in MDD.