Two-dimensional horizontal visibility graph analysis of human brain aging on gray matter

Abstract Characterizing the trajectory of the healthy aging brain and exploring age-related brain structural changes can help deepen our understanding of the mechanism of brain aging. Currently, most structural magnetic resonance imaging literature explores brain aging merely from the perspective of morphological features, which cannot fully utilize the gray-scale values containing important intrinsic information about brain structure. In this study, we proposed to construct two-dimensional horizontal visibility graphs based on the pixel intensity values of the gray matter slices directly. Afterward, the normalized network structure entropy (NNSE) was introduced to quantify the overall heterogeneities of these graphs. The results demonstrated decreased between the NNSEs of gray matter and ages. Compared with the middle-aged and the elderly, the larger values of the NNSE in the young group may indicate the more homogeneous network structures, the smaller differences in importance between nodes, and thus a more powerful intrusion tolerance ability. In addition, the hub nodes of different adult age groups are primarily located in the precuneus, cingulate gyrus, superior temporal gyrus, inferior temporal gyrus, parahippocampal gyrus, insula, precentral gyrus, and postcentral gyrus. Our study can provide a new perspective for understanding and exploring the structural mechanism of brain aging.