Abstract
IntroductionUnderstanding the neural basis underlying major depressive disorder (MDD) is essential for the diagnosis and treatment of this mental disorder. Aberrant activation and functional connectivity of the default mode network (DMN) have been consistently found in patients with MDD. It is not known whether effective connectivity within the DMN is altered in MDD.ObjectsThe primary object of this study is to investigate the effective connectivity within the DMN during resting state in MDD patients before and after eight weeks of antidepressant treatment.MethodsWe defined four regions of the DMN (medial frontal cortex, posterior cingulate cortex, left parietal cortex, and right parietal cortex) for each participant using a group independent component analysis. The coupling parameters reflecting the causal interactions among the DMN regions were estimated using spectral dynamic causal modeling (DCM).ResultsTwenty‐seven MDD patients and 27 healthy controls were included in the statistical analysis. Our results showed declined influences from the left parietal cortex to other DMN regions in the pre‐treatment patients as compared with healthy controls. After eight weeks of treatment, the influence from the right parietal cortex to the posterior cingulate cortex significantly decreased.ConclusionThese findings suggest that the reduced excitatory causal influence of the left parietal cortex is the key alteration of the DMN in patients with MDD, and the disrupted causal influences that parietal cortex exerts on the posterior cingulate cortex is responsive to antidepressant treatment.
Highlights
Understanding the neural basis underlying major depressive disorder (MDD) is essential for the diagnosis and treatment of this mental disorder
The mean connections from left parietal cortex (LPC) to medial frontal cortex (MFC), posterior cingulate cortex (PCC) and right parietal cortex (RPC) increased in the post-treatment group, but these increased connections do not show the significant difference between the pre-treatment MDD and post- treatment MDD group with paired t-test
We did not detect any significant increase in the connections from the LPC to MFC, RPC or PCC with the improvement of the symptoms, which were diminished in the pre-treatment MDD group
Summary
Major Depressive Disorder (MDD) is a psychiatric disorder characterized by persistent symptoms that interfere with daily life (American Psychiatric Association, 2000) and it is an increasing burden to society. The DMN has been associated with self- referential processes (Broyd et al, 2009; Gusnard, Akbudak, Shulman, & Raichle, 2001) and may be separable into anterior (ventromedial prefrontal cortex) and posterior (posterior cingulate cortex) components (Andrewshanna, Smallwood, & Spreng, 2014; Uddin, Kelly, Biswal, Castellanos, & Milham, 2009) It has been implicated among the most discriminating networks classifying MDD patients from healthy controls (Zeng et al, 2012). Traditional functional connectivity measures correlations between brain regions based upon time series, without providing directed or causal interactions underlying the observed correlations (Friston, Harrison, & Penny, 2003) It remains unknown whether causal interactions within the DMN are impaired in patients with MDD. The coupling parameters between the DMN regions were compared at the group level, and the relationship between coupling parameters and the clinical scores were analyzed
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