Differential Age-Related Changes in Structural Covariance Networks of Human Anterior and Posterior Hippocampus

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 and the posterior hippocampus. In this study, 240 healthy subjects aged 18 to 89 were selected and subdivided into young (18-23 years), middle-aged (30-58 years) and older (61-89 years) groups. The anterior and posterior hippocampus were 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 anterior and posterior hippocampus had different structural covariance patterns, but both of them were associated with the medial temporal lobe and insula. Moreover, both increased and decreased covariance were found with the anterior hippocampus but only increased covariance was found with the posterior hippocampus with age (p < 0.05, FWE 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 anterior and posterior hippocampus, providing an essential insight into the mechanisms of the hippocampus in normal aging.