Abstract
Altered function of the medial temporal lobe (MTL) is a valuable indicator of conversion from amnestic mild cognitive impairment (aMCI) to Alzheimer’s disease. This study is to delineate the functional circuitry of multiple subdivisions of parahippocampal gyrus and hippocampus (HIP) and to examine how this knowledge contributes to a more principled understanding of the contributions of its subregions to memory in aMCI. The functional connectivity (FC) analysis was performed in 85 aMCI and 129 healthy controls. The aMCI demonstrated the distinct disruptive patterns of the MTL subregional connectivity with the whole-brain. The right entorhinal cortex (ERC) and perirhinal cortex (PRC) showed increased connectivity with the left inferior and middle occipital gyrus, respectively, which potentially indicated a compensatory mechanism. Furthermore, the right altered MTL subregional FC was associated with episodic memory performance in aMCI. These results provide novel insights into the heterogeneous nature of its large-scale connectivity in MTL subregions in memory system underlying the memory deficits in aMCI. It further suggests that altered FC of MTL subregions is associated with the impairment of the differential encoding stages of memories and the functional changes in the specific right HIP-ERC-PRC-temporal circuitry may contribute to the impairment of episodic memory in aMCI.
Highlights
Connectivity, the anterolateral and posteromedial ERC are related to a relative segregation of object and spatial information processing, respectively[13]
We further predicted that the altered functional connectivity (FC) in a specific pathway along the medial temporal lobe (MTL) cortical processing hierarchy system would link to the impairment of episodic memory in Amnestic mild cognitive impairment (aMCI)
Both in aMCI and healthy controls (HC), spontaneous activity in the MTL subregions strongly correlated with activities in a widely-distributed set of cortical and subcortical regions, as well as cerebellum
Summary
Connectivity, the anterolateral and posteromedial ERC are related to a relative segregation of object and spatial information processing, respectively[13]. Several neuroimaging evidences indicate that aMCI can be characterized by abnormalities in resting-state FC of MTL subregions[20–23] These above-mentioned studies do not explore the full-scale information of whole brain, or manually draw regions of interest (ROIs), or only provide results in coarsely divided subregions of the HIP and a limited view of MTL circuitry. We further predicted that the altered FC in a specific pathway along the MTL cortical processing hierarchy system would link to the impairment of episodic memory in aMCI To answer this issue, the present study evaluated the connectivity patterns based on two parallel arrays of seeds along the longitudinal axis of the parahippocampal gyrus (PHG) and the HIP in each hemisphere (Fig. 1A,B for detailed data analysis pipeline)
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