Abstract
Recent studies about brain network have suggested that normal aging is associated with alterations in coordinated patterns of the large-scale brain functional and structural systems. However, age-related changes in functional networks constructed via positron emission tomography (PET) data are still barely understood. Here, we constructed functional brain networks composed of regions in younger (mean age years) and older (mean age years) age groups with PET data. younger and older healthy individuals were separately selected for two age groups, from a physical examination database. Corresponding brain functional networks of the two groups were constructed by thresholding average cerebral glucose metabolism correlation matrices of regions and analysed using graph theoretical approaches. Although both groups showed normal small-world architecture in the PET networks, increased clustering and decreased efficiency were found in older subjects, implying a degeneration process that brain system shifts from a small-world network to regular one along with normal aging. Moreover, normal senescence was related to changed nodal centralities predominantly in association and paralimbic cortex regions, e.g. increasing in orbitofrontal cortex (middle) and decreasing in left hippocampus. Additionally, the older networks were about equally as robust to random failures as younger counterpart, but more vulnerable against targeted attacks. Finally, methods in the construction of the PET networks revealed reasonable robustness. Our findings enhanced the understanding about the topological principles of PET networks and changes related to normal aging.
Highlights
Function decline and organs aging is an inevitable physiological law of life
Previous studies found that normal aging processes significantly affect default mode network (DMN) [20,21,22,23], which is typically deactivated during external stimulation [24,25]
Our main results are as follows: (1) that the observed data demonstrate age-related alterations in functional correlations among selective subsets of regions, (2) that the global topological organization of functional networks in older subjects are disrupted as indicated by altered small-world parameters, (3) that the regional nodal characteristic is changed in older subjects, (4) that the functional network of older group shows reduced network robustness in response to the targeted attack, (5) that the methods to construct the functional positron emission tomography (PET) networks demonstrate reasonable robustness
Summary
Function decline and organs aging is an inevitable physiological law of life. As one of the most important organs, aging brain tends to produce some specific alterations in morphological, physiological pathology and functional aspects. The functional and structural systems of the human brain reveal age-related topological properties of complex networks, such as small-world characteristics, highly connected hubs, modularity, and network robustness [7,9,10,8,11]. Some recent studies reported that, along with the normal aging, small-world network showed changed topological efficiency [10,14,15,16]. Changes in modular organization of human brain networks were proven to be associated with normal aging [9,15]. Highly connected hubs are altered with normal aging, which has been reported in some previous studies [9,7]. A gradually forming evaluated system of brain networks with neural imaging technologies was adopted in assessing the aging brain and provided a guiding for age-related encephalopathy in clinical [7,8]
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