The Magnetic Resonance Imaging Study On Brain Network Connections In First-Episode, Treatment-Naive Young Adults With Major Depressive Disorder

ObjectiveThe aim of the study is to explore the possible changes in brain structural and functional connection in first-episode, treatment-naive young adults with major depressive disorder (MDD), in order to investigate the disease-specific biological makers and to provide new evidences for the understanding the mechamism and diagnosis of MDD.(1) to explore structural integrity of white matter by means of diffusion tensor imaging and the correlationship with the depressive symptoms in first-episode, treatment-naive young adults with MDD.(2) to explore resting-state functional connectivity of default mode network and the correlationship with the depressive symptoms in first-episode, treatment-naive young adults with MDD.Methods(1) DTI was performed in 30 first-episode, treatment-naive young adult patients with MDD and 30 healthy controls matched for age, gender and education. A whole-brain statistical comparison method called tract-based spatial statistics (TBSS) was used to analyze the data. The white matter difference between the patients and the controls was examined. Then the the severity of depressive symptoms, age at onset of illness and illness duration were introduced to examine their relationship with white matter of depressive patients.(2) We analyzed the resting-state fMRI data from 35 first-episode, treatment-naive young adults with MDD and 35 age-, gender-and education-matched healthy controls. A method called by independent component analysis (ICA) was used to analyze the resting-state data and the rule of goodness-of-fit was used to choose the independent component. The difference of default mode network (DMN) between the patients and the controls was examined. Then rumination and autobiographical memory were introduced to examine their relationship with the DMN of the depressive patients.Results(1) Compared with healthy controls, patients with MDD showed decreased fractional anisotropy (FA) values in three white matter (WM) tracts:the left anterior limb of the internal capsule, the right parahippocampal gyrus and the left posterior cingulate cortex. Further analysis revealed that FA values in the left anterior limb of the internal capsule were negatively correlated with the severity of depressive symptoms. No regions showed higher FA in MDD patients than in controls.(2) Patients with MDD exhibited higher levels of rumination and autobiographical memory than the controls. We observed increased functional connectivity in the anterior medial cortex region [especially the medial prefrontal cortex (MPFC) and anterior cingulate cortex (ACC)], and decreased functional connectivity in the posterior medial cortex region [especially the posterior cingulate cortex/precuneus (PCC/precuneus)] in MDD patients compared with the controls. Within the depressed group, the increased functional connectivity in anterior medial cortex correlated positively with rumination score, while the decreased functional connectivity in posterior medial cortex correlated negatively with OGM score.ConclusionsThe MDD showed the abnormal WM microstructral integrity and resting-state DMN.(1) The present results support the hypothesis that altered WM integrity, especially in the cortical-subcortical neural circuit, may contribute to the pathophysiology of MDD. Furthermore, these findings provide novel evidence that microstructural abnormalities in WM may occur early in the course of depression.(2) We reported a dissociation between anterior and posterior functional connectivity in resting-state DMNs of first-episode, treatment-naive young adults with MDD. Rumination may be mediated by increased functional connectivity in anterior medial regions whereas overgeneral autobiographical memory (OGM) may be mediated by decreased functional connectivity in posterior medial regions of the resting-state DMN. These results provided new evidence for the importance of the DMN in the pathophysiology of MDD and suggested abnormal DMN activity may be an MDD trait.