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Abstract
The hippocampus plays an important role in memory function relying on information interaction between distributed brain areas. The hippocampus can be divided into the anterior and posterior sections with different structure and function along its long axis. The aim of this study is to investigate the effects of normal aging on the structural covariance of the anterior hippocampus (aHPC) and the posterior hippocampus (pHPC). In this study, 240 healthy subjects aged 18–89 years were selected and subdivided into young (18–23 years), middle-aged (30–58 years), and older (61–89 years) groups. The aHPC and pHPC was divided based on the location of uncal apex in the MNI space. Then, the structural covariance networks were constructed by examining their covariance in gray matter volumes with other brain regions. Finally, the influence of age on the structural covariance of these hippocampal sections was explored. We found that the aHPC and pHPC had different structural covariance patterns, but both of them were associated with the medial temporal lobe and insula. Moreover, both increased and decreased covariances were found with the aHPC but only increased covariance was found with the pHPC with age (p < 0.05, family-wise error corrected). These decreased connections occurred within the default mode network, while the increased connectivity mainly occurred in other memory systems that differ from the hippocampus. This study reveals different age-related influence on the structural networks of the aHPC and pHPC, providing an essential insight into the mechanisms of the hippocampus in normal aging.
Highlights
With the population aging, understanding normal brain changes are as important as understanding demented diseases
Four separate regression analyses were executed on the modulated gray matter (GM) images data to map structural covariance network (SCN) of the bilateral anterior hippocampus (aHPC) and posterior hippocampus (pHPC) in the young group
We found that the SCNs seeding from the aHPC and pHPC in the young adults were different from each other, but both of them related with the medial temporal lobe and insula
Summary
With the population aging, understanding normal brain changes are as important as understanding demented diseases. Memory decline is a typical characteristic of normal aging. The hippocampus is considered critical in human memory and spatial navigation (Scoville and Milner, 1957; Buzsáki and Moser, 2013). Evidence suggests that hippocampal volume changes throughout the lifespan, which stays relatively stable until the age of 60 shows a sharp decline (Raz et al, 2010; Schuff et al, 2012; Fjell et al, 2013). Functional imaging studies have revealed and hypometabolism (de Leon et al, 2001; Wu et al, 2008) of the hippocampus in aging. A reduced fractal dimension of hippocampal dynamics with age was reported (Goldberger et al, 2002; Wink et al, 2006)
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