Abnormal functional connectivity density in patients with major depressive disorder with comorbid insomnia

Background: Insomnia is a common comorbidity symptom in patients with major depressive disorder (MDD). However, the brain functional alteration in MDD with higher level insomnia (MDD-HI) and lower level insomnia (MDD-LI) remains unclear. Here, we investigated the association of insomnia with global functional connectivity density (gFCD) in patients with MDD. Methods: A total of 148 participants were recruited and underwent resting-state functional magnetic resonance imaging. A voxel-wise analysis of covariance was employed to explore group differences in gFCD among the MDD-HI, MDD-LI and healthy control (HC) groups. Results: The gFCD in the bilateral parahippocampal/hippocampal gyri (PHG/HIP) was higher in the two MDD than in the HC group, and it was higher in the MDD-LI than in the MDD-HI group; the gFCD in the left fusiform area was lower in the MDD than in the HC group. The gFCD in the left inferior temporal gyrus (ITG) was higher in the MDD-HI than in the MDD-LI and HC groups. The gFCD in the left ITG and posterior PHG/HIP was associated with insomnia, while the gFCD in the left anterior PHG/HIP was correlated with non-insomnia depressive symptoms in the MDD group. Limitations: The cross-sectional design and the use of brief/subjective insomnia assessments. Conclusions: The present study showed that the abnormal brain features of MDD with different insomnia symptom. Importantly, the posterior and anterior parts of the hippocampus may play different roles in the presence or absence of insomnia in patients with MDD.