Functional PET Brain Network And Age--related Changes

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. It is well known that normal aging is associated with a progressive decline in cognitive performance, including perception, attention, language and memory. Meanwhile, normal senescence is also highly related to some specific encephalopathy, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Therefore, aiming to assess the declining cognitive ability and supply a guiding for age-related encephalopathy in clinical, it is necessary to deeply understand the age-related changes in healthy brain.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 of90regions in younger (mean age=36.5years) and older (mean age=56.3years) age groups with PET data.113younger and110older 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 of90regions 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.