Abstract
The aim of this study was to investigate age-related changes in the topological organization of structural brain networks by applying a longitudinal design over 6 years. Structural brain networks were derived from measurements of regional gray matter volume and were constructed in age-specific groups from baseline and follow-up scans. The structural brain networks showed economical small-world properties, providing high global and local efficiency for parallel information processing at low connection costs. In the analysis of the global network properties, the local and global efficiency of the baseline scan were significantly lower compared to the follow-up scan. Moreover, the annual rate of change in local and global efficiency showed a positive and negative quadratic correlation with the baseline age, respectively; both curvilinear correlations peaked at approximately the age of 50. In the analysis of the regional nodal properties, significant negative correlations between the annual rate of change in nodal strength and the baseline age were found in the brain regions primarily involved in the visual and motor/control systems, whereas significant positive quadratic correlations were found in the brain regions predominately associated with the default-mode, attention, and memory systems. The results of the longitudinal study are consistent with the findings of our previous cross-sectional study: the structural brain networks develop into a fast distribution from young to middle age (approximately 50 years old) and eventually became a fast localization in the old age. Our findings elucidate the network topology of structural brain networks and its longitudinal changes, thus enhancing the understanding of the underlying physiology of normal aging in the human brain.
Highlights
Recent advances in generating a network map of the human brain, known as the human connectome, provided new insights into structural and functional connectivity patterns of the human brain (Sporns et al, 2005; Bullmore and Bassett, 2011; Sporns, 2011a,b)
ECONOMICAL SMALL-WORLD PROPERTIES AND LONGITUDINAL CHANGES The structural brain networks of the age-specific groups exhibited economical small-world properties, showing higher local efficiency but similar global efficiency compared to the matched random networks (Latora and Marchiori, 2001)
Significant differences in the summary local efficiency were found in several age groups across the baseline age but those in the summary global efficiency were found in the middle age groups (Figure 3)
Summary
Recent advances in generating a network map of the human brain, known as the human connectome, provided new insights into structural and functional connectivity patterns of the human brain (Sporns et al, 2005; Bullmore and Bassett, 2011; Sporns, 2011a,b). Prodigious efforts in the study of the human connectome have greatly expanded our knowledge of the topological principles of brain network organization in the healthy, developing, aging, and diseased brains (Bassett and Bullmore, 2009; Uddin et al, 2010; Lo et al, 2011; Xia and He, 2011; Xie and He, 2011; Greicius and Kimmel, 2012; Sun et al, 2012) It has been well-established that advanced aging is accompanied by cognitive decline, even in the absence of disease. We hypothesized that significant longitudinal changes might occur in the topological properties of structural brain networks with normal aging
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