Abstract
A large number of morphology-based studies have previously reported a variety of regional abnormalities in hemispheric asymmetry in Alzheimer’s disease (AD). Recently, neuroimaging studies have revealed changes in the topological organization of the structural network in AD. However, little is known about the alterations in topological asymmetries. In the present study, we used diffusion tensor image tractography to construct the hemispheric brain white matter networks of 25 AD patients, 95 mild cognitive impairment (MCI) patients, and 48 normal control (NC) subjects. Graph theoretical approaches were then employed to estimate hemispheric topological properties. Rightward asymmetry in both global and local network efficiencies were observed between the two hemispheres only in AD patients. The brain regions/nodes exhibiting increased rightward asymmetry in both AD and MCI patients were primarily located in the parahippocampal gyrus and cuneus. The observed rightward asymmetry was attributed to changes in the topological properties of the left hemisphere in AD patients. Finally, we found that the abnormal hemispheric asymmetries of brain network properties were significantly correlated with memory performance (Rey’s Auditory Verbal Learning Test). Our findings provide new insights into the lateralized nature of hemispheric disconnectivity and highlight the potential for using hemispheric asymmetry of brain network measures as biomarkers for AD.
Highlights
Alzheimer’s disease is the most common form of dementia, comprising an estimated 60-80% of all dementia cases, and mild cognitive impairment (MCI) is considered a prodromal state of AD and possibly other dementias in which cognitive decline is greater than expected at a certain age or education level, but with functional impairment that is insufficient for a diagnosis of dementia (Petersen et al, 1985)
Within-Group Asymmetry In addition, we found that normal control (NC) subjects exhibited no significant difference in two hemispheric brain white matter (WM) networks, suggesting that the two hemispheres showed similar intra-connected pathways in NC
The present study revealed increased rightward asymmetry in hemispheric brain WM networks from NC to MCI to AD, and the rightward asymmetry is attributed to aberration of topological properties in the left hemisphere in patients
Summary
MATERIALS AND METHODSAlzheimer’s disease is the most common form of dementia, comprising an estimated 60-80% of all dementia cases, and MCI is considered a prodromal state of AD and possibly other dementias in which cognitive decline is greater than expected at a certain age or education level, but with functional impairment that is insufficient for a diagnosis of dementia (Petersen et al, 1985). There is aberrant hemispheric asymmetry in WM properties (Müller et al, 2005; Damoiseaux et al, 2009; Stricker et al, 2009; Liu et al, 2011; Wessa et al, 2016) and functional connectivity (Wang et al, 2006, 2015) Some of these studies showed that the left hemisphere was significantly more impaired than the right, indicating a faster left hemisphere degeneration in AD (Thompson et al, 2003, 2007; Müller et al, 2005; Damoiseaux et al, 2009; Li et al, 2016; Wessa et al, 2016). The entire k-core was “lost” in the left hemisphere of AD subjects, supporting lateralized deficits in connectome topologies of AD
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