Baseline and longitudinal patterns of hippocampal connectivity in mild cognitive impairment: evidence from resting state fMRI

The hippocampus is believed to have close relationship with many cerebral cortexes and constitute memory network to modulate and facilitate communication, which makes it especially interesting and meaningful in the study of functional connectivity in mild cognitive impairment (MCI). However, functional connectivity between the hippocampus and other brain regions remains unclear in MCI. Furthermore, the longitudinal changes of the hippocampal connectivity have not been reported. In the study, resting state functional MRI (fMRI) was used to examine changes in hippocampal connectivity comparing 14 patients and 14 healthy age-matched controls. We found that functional connectivity between the hippocampus and a set of regions was disrupted in MCI, these regions are: the right frontal lobe, the bilateral temporal lobe and the right insular. While, the left posterior cingulate cortex, precuneus, hippocampus, caudate and right occipital gyrus showed increased connectivity to the hippocampus in MCI. Additionally, we traced the seven MCI patients and compared the hippocampal connectivity in initial stage and 3 years later stage. Several regions presented decreased connectivity to the hippocampus after 3 years. Finally, the hippocampal connectivity with some regions showed significant correlation with the cognitive performance of patients. Based on these findings, the decreased hippocampal connectivity might indicate reduced integrity of hippocampal cortical memory network in MCI. In addition, the increased hippocampal connectivity suggested compensation for the loss of memory function. With the development of the disease, the hippocampal connectivity may lose some compensation and add some more disruption due to the pathological changes.