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Sleep disturbance is one of the most frequent somatic symptoms in major depressive disorder (MDD), but the neural mechanisms behind it are not well understood. Sleep efficiency (SE) is a good indicator of early awakening and difficulty falling asleep in MDD patients. Our study aimed to investigate the relationship between sleep efficiency and brain function in MDD patients. We recruited 131 MDD patients from the Fourth People's Hospital in Hefei, and 71 well-matched healthy controls who were enrolled from the community. All subjects underwent resting-state functional MRI. Brain function was measured using the fractional amplitude of low-frequency fluctuation (fALFF), sleep efficiency was objectively measured by polysomnography (PSG), and clinical scales were used to evaluate depressive symptoms and sleep status. Multivariate regression analysis was performed to assess the relationship between the amplitude of the low frequency fluctuation fraction and sleep efficiency. Three brain regions with relevance to sleep efficiency in MDD patients were found: inferior occipital gyrus (Number of voxels = 25, peak MNI coordinate x/y/z = −42/-81/-6, Peak intensity = 4.3148), middle occipital gyrus (Number of voxels = 55, peak MNI coordinate x/y/z = −30/-78/18, Peak intensity = 5.111), and postcentral gyrus (Number of voxels = 26, peak MNI coordinate x/y/z = −27/-33/60, Peak intensity = 4.1263). But there was no significant relationship between fALFF and SE in the healthy controls. The reduced sleep efficiency in MDD may be related to their lower neural activity in the inferior occipital gyrus, middle occipital gyrus, and postcentral gyrus. The findings may provide a potential neuroimaging basis for the clinical intervention in patients with major depressive disorder with sleep disturbances. [ABSTRACT FROM AUTHOR]

There is evidence that major depressive disorder (MDD) is related to serum lipid level alterations. However, the neural correlates underlying this association remain poorly understood. Forty-nine patients with MDD and fifty healthy controls (HCs) underwent structural, resting-state functional and diffusion magnetic resonance imaging scans. Voxel-based morphometry, functional connectivity (FC) and tract-based spatial statistics analyses were performed to assess brain structure and function, respectively. Blood samples were collected to measure serum levels of lipid variables including total cholesterol, triglyceride and high density lipoprotein cholesterol (HDL-C). Correlation and mediation analyses were conducted to investigate the associations of serum lipid levels with brain imaging measures in MDD patients and HCs, respectively. We found that the serum HDL-C level in MDD patients was lower than that in HCs. The lower serum HDL-C level was associated with lower gray matter volume (GMV) in ventromedial prefrontal cortex (VMPFC), higher within-network FC of the default mode network, and lower micro-structural integrity in multiple white matter regions in MDD patients. Moreover, the within-default mode network FC mediated the relationship between GMV in VMPFC and serum HDL-C level; white matter integrity in genu of corpus callosum mediated the relationship between serum HDL-C level and depressive symptom severity. However, we did not observe any correlations between serum lipids and brain imaging parameters in HCs. These findings help to identify neural correlates underlying the association between depression and serum HDL-C change, which may provide new insight into intervention, treatment and prevention of depression from the perspective of regulating serum lipids. • Depression patients had lower serum high density lipoprotein cholesterol level. • It was associated with lower gray matter volume in ventromedial prefrontal cortex. • It was associated with higher functional connectivity in default mode network. • It was associated with lower micro-structural integrity in multiple white matter regions. • Mediation relationships were observed between serum lipid, brain, depressive symptom. [ABSTRACT FROM AUTHOR]