A Research On Dynamic Characteristics Of White Matter Functional Networks Via MRI Data

The brain is the most complex system,consisting of many neurons working together to perform various advanced functions.Blood oxygen level-dependent（BOLD）,due to its noninvasiveness in addition to high spatial and temporal resolution,has emerged as the most widely used functional magnetic resonance imaging（fMRI）method to study the brain.Dynamic functional connectivity can capture the subtle time variation of human brain activities and provide essential biomarkers for pathological studies of related brain diseases.In addition to gray matter,white matter occupies half the volume of the brain,and extensive pathological and anatomical studies have confirmed the functional significance of the white matter.However,the spatiotemporal dynamics of white matter are still unclear.This study used the multimodal brain functional and structural images of the human connection project to identify 9 gray matter and 9 white matter functional networks.We used the Kmeans clustering technique and evaluated the reliability of static and dynamic functional connectivity by calculating the test’s intraclass correlation coefficients.We also performed static and dynamic functional connectivity and respective intraclass corre-lation coefficients of gray matter functional networks（GM-FNs）,white matter functional networks（WM-FNs）,and gray matter-white matter functional networks（GM-WM-FNs）.The results shows that the static functional connectivity of GM-FNs is stronger than that of WM-FNs,but the corresponding dynamic functional connectivity is lower,indicating that WM-FNs are more unstable.In the GM-FNs/WM-FNs,their static functional connectivity and dynamic functional connectivity have a similar correlation.These results indicate that the BOLD signal of white matter fMRI contains dynamic spatiotemporal information similar to that of gray matter and may provide important clues for further understanding the information exchange between the functional organizations of the brain.We also studied the changes in the dynamic functional connectivity patterns of the bilateral hippocampus and the whole brain in patients with mild cognitive impairment（MCI）and very mild cognitive impairment（VMCI）in the resting state.We found that several brain areas with significant enhancement,including Putamen_R,Cerebelum_Crusl_L,Cerebelum_6L and significantly weakened brain areas（Cerebelum_9L,Temporal_Mid_L,Cingulum_Mid_L,Thalamus_L,Precuneus,Vermis₈,Caudate_L）.Most of these brain areas are in the default network and cerebellum area,which reveals that the abnormal dynamic functional connectivity between the hippocampus and the default network may be one of the mechanisms of Alzheimer’s disease（AD）cognitive and episodic memory’s physiological changes impairment.The abnormal connection between the hippocampus and the cerebellum region also reminds us that the cerebellum and the brain interact and coordinate to complete cognitive functions together.We also found low dynamic functional connectivity variability in the bilateral hippocampus and Cerebellum Anterior Lobe-white matter,corpus callosum and Frontal Lobe-white matter in patients with MCI and VMCI.These results indicate that white matter lesions are an important cause of cognitive decline in AD patients.