To assess abnormal default mode network (DMN) and its potential mechanisms in insomnia patients with varying depression symptom via resting state functional magnetic resonance imaging (fMRI).

We recruited 15 cases of primary insomnia (PI) without depression symptom, 40 cases of insomnia patients with varying depressions, including mild depression (n=20) and moderate depression (n=20), and 40 cases of healthy controls (HC) with age and gender matched. We set bilateral posterior cingulate cortex and precuneus (PCC/PC) as seed regions, and compared the DMN changes between HC group and PI with depression symptoms group. We then compared the DMN changes between PI with mild and moderate depression groups. Finally, we extracted right cingulate cortex and parahippocampal signals and made Pearson correlation coefficient analysis with the Hamilton Depression Scale (HAMD) scores.

The connectivity of PI with depression symptoms group was increased in brain regions including bilateral precuneus, left middle occipital gyrus, superior parietal lobe, superior frontal lobe, and was decreased in brain regions including left anterior cingulate cortex, compared with HC group. Compared with PI without depression symptoms group, the connectivity of PI with mild depression symptoms group was decreased in brain regions including bilateral middle frontal gyrus, right middle occipital gyrus/precuneus, and was not increased in brain regions in insomnia with mild group. Compared with PI with mild depression symptoms group, the connectivity of PI with moderate depression symptoms group was increased in brain regions including right cerebellum posterior lobe, middle cingulate cortex, left insular lobe/inferior frontal lobe, extra nuclear and inferior parietal lobe, and was decreased in brain regions in insomnia with moderate depression symptoms group including left superior temporal lobe and right parahippocampal gyrus. Pearson correlation coefficient analysis showed significant correlation between signals of right parahippocampal gyrus and HAMD scores (r=-0.697, P=0.006), while not between signals of right middle cingulate cortex and HAMD scores (r=0.224, P=0.441).

There were abnormal DMN in PI with depression symptoms group, and in PI with varying degrees of depression symptoms groups. Our results revealed specified brain regions of cognitive dysfunction and neural pathological mechanisms which were affected by PI with depression symptom.

Sleep initiation and maintenance disorders; Depression; Nerve net; Magnetic resonance imaging