The Structural And Network Alterations In Subcortical Vascular Mild Cognition Impairment With And Without Depressive Symptoms

Considering the high incidence and disability rate,dementia is attracting worldwide attention and becoming a global issue.Vascular dementia is the second most common type of dementia and even has a higher disability rate than Alzheimer's disease?AD?.Vascular mild cognitive impairment is prodromal stage to vascular dementia.Mild cognitive impairment that caused by subcortical vascular disease?svMCI?is one of the subtypes of the vascular mild cognitive impairment.With the development of neuroimaging,magnetic resonance imaging?MRI?plays an important role in the research of brain science.Diffusion tensor imaging?DTI?has been widely used to explore white matter microstructure in many neuropsychiatric diseases with excellent results.In this study,we used DTI to study the white matter structure in the subcortical vascular mild cognitive impairment?svMCI?.This study consists of two parts.Part 1,we aimed to identify the alterations of white matter microstructure in svMCI with or without depressive symptoms,since svMCI patients are often clinically accompanied by depressive symptoms but the mechanism is still unclear.In this part,18 svMCI with depressive symptoms?svMCI+D?,17 svMCI without depressive symptoms?svMCI-D?and 23 normal control?NC?were included.They were underwent neuropsychological tests and MRI scans and signed informed consents.Montreal Cognitive Assessment test?MOCA?and Hamilton Depression Rating Scale?HAMD?were used to measure cognitive impairment and depressive symptoms,respectively.Fractional anisotropy?FA?and mean dispersion?MD?were used to measure the integrity of white matter microstructure.Chi-square test,one-way analysis of variance and two sample t test were used to perform the statistical comparison.Finally,Pearson correlations were used to analyze the correlation between FA/MD and MOCA/HAMD scores.As a result,svMCI+D and svMCI-D patients showed decreased FA of bilateral insula and left precentral gyrus and increased MD of cerebellum when compared with NC.Compared with svMCI-D,svMCI+D showed increased FA of left precentral gyrus.Moreover,there was a positive correlation between MD of the cerebellum and HAMD of svMCI+D patients.All the results were statistically significant?p<0.05?.These results showed that the microstructures of the insula,the left precentral gyrus and the cerebellum of svMCI patients were damaged.Among these,the white matter changes in the left precentral gyrus and cerebellum may be related to the depression symptoms in svMCI patients.The cerebellum damage might be secondary to the damage in the left precentral gyrus,but further studies are needed to confirm it.Part 2.Network neuroscience is in a period of vigorous development.Graph theory provides a complete theoretical framework for the research of network neuroscience.Different neuropsychiatric diseases showed specific pattern of network,which indicates that it is clinically significant to explore brain network of svMCI.In this part,32 svMCI and 37 NC were included.The inclusion criteria were similar to the part 1.Differently,we just use MOCA to measure the cognitive function.Deterministic fiber tracing method and graph-theory were used to construct the white matter structural network of svMCI and NC.Characteristic path length?L_p?,Clustering coefficient?C_p?,small-worldness,global efficiency?E_g?and local efficiency(E_loc)were used to evaluate the whole network.Nodal efficiency(E_nodal)and degree centrality?DC?were used to measure the changes of node.Chi-square test and two sample t test were used for statistical analysis.Finally,Pearson correlations were used to analyze the relationships between the changed network parameters and MOCA scores.Consequently,white matter networks of svMCI patients and NC are small-world networks.Compared with NC,svMCI patients showed increased Lp and decreased Eg.But,there was no significant difference in the Cp and E_loc.Compared with NC,svMCI showed decreased E_loc of right Rolandic operculum,left posterior cingulate gyrus,left calcarine fissure and surrounding cortex and left inferior temporal gyrus.Meanwhile,the DC of the left inferior temporal gyrus in svMCI decreased.However,no changes showed correlation with MOCA scores.This study shows that the white matter network of svMCI was small-world networks.However,the topological structure of the network is changed,which indicates that function integration ability of the network is reduced.Damage to the long connections of the operculum,cingulate gyrus and temporal lobe may be an important reason for the decreased efficiency of the global network.