Abstract
Mild behavioral impairment (MBI), characterized by the late-life onset of sustained and meaningful neuropsychiatric symptoms, is increasingly recognized as a prodromal stage of dementia. However, the underlying neural mechanisms of MBI remain unclear. Here, we examined alterations in the topological organization of the structural covariance networks of patients with MBI (N = 32) compared with normal controls (N = 38). We found that the gray matter structural covariance networks of both the patients with MBI and controls exhibited a small-world topology evidenced by sigma value larger than one. The patients with MBI had significantly decreased clustering coefficients at several network densities and local efficiency at densities ranging from 0.05 to 0.26, indicating decreased local segregation. No significant differences in the characteristic path length, gamma value, sigma value, or global efficiency were detected. Locally, the patients with MBI showed significantly decreased nodal betweenness centrality in the left middle frontal gyrus, right inferior frontal gyrus (opercular part), and left Heschl gyrus and increased betweenness centrality in the left gyrus rectus, right insula, bilateral precuneus, and left thalamus. Moreover, the difference in the bilateral precuneus survived after correcting for multiple comparisons. In addition, a different number and distribution of hubs was identified in patients with MBI, showing more paralimbic hubs than observed in the normal controls. In conclusion, we revealed abnormal topological patterns of the structural covariance networks in patients with MBI and offer new insights into the network dysfunctional mechanisms of MBI.
Highlights
Mild behavioral impairment (MBI) is a neurobehavioral syndrome characterized by the late-life onset of sustained and meaningful neuropsychiatric symptoms (NPSs) of any severity that other formal medical and psychiatric nosologies cannot account for Mortby et al (2018)
This study showed that the structural covariance networks of both groups followed a small-world topology across the range of densities, as evidenced by sigma values greater than one (Figure 1D)
In line with these studies, we found that the gray matter (GM) structural covariance networks of both patients with MBI and controls showed a small-world topology, which provided further evidence supporting the notion that smallworld topology is a fundamental organizational principle of structural brain networks
Summary
Mild behavioral impairment (MBI) is a neurobehavioral syndrome characterized by the late-life onset of sustained and meaningful neuropsychiatric symptoms (NPSs) of any severity that other formal medical and psychiatric nosologies cannot account for Mortby et al (2018). A large-scale study on cognitively normal individuals showed that individuals with MBI had significantly worse cognitive performance at baseline and a significantly greater decline in attention and working memory over 1 year (Creese et al, 2019). Another longitudinal study on cognitively normal individuals reported that of those who progressed from being normal to MCI or dementia, more than 59% developed NPSs before the diagnosis of any cognitive disorder (Wise et al, 2019). A recent study involving community-dwelling adults showed an association of apathy with an increased risk of developing probable dementia (Bock et al, 2020).
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