Study of functional and metabolic changes in subregions of precuneus in mild cognitive impairment patients using hybrid FDG-PET/fMRI

Characterization of the pathological changes in mild cognitive impairment (MCI) might provide useful biomarkers for early detection of individuals at high risk for MCI to Alzheimer's disease (AD) conversion. Previous studies have shown that the disrupted functional connectivities (FCs) between the precuneus (PCu) and large-scale brain functional networks are involved in early-stage AD pathology. Yet the findings in MCI are various, which might be due to the heterogeneous functions of the subregions of PCu. Also, the underlying metabolic mechanism remains unclear. In this study, using a hybrid 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) and functional magnetic resonance imaging (fMRI) approach, we investigated the FC changes between the functional subregions of PCu, i.e., the dorsal-anterior (DA_pcu), dorsal-posterior (DP_pcu), and ventral precuneus (V_pcu), to large-scale brain functional networks, i.e., the default mode network (DMN), the frontoparietal network (FPN) and the visual network (VIS), in relation to the local glucose metabolism in healthy controls and MCI patients. For DP_pcu, the MCI patients showed reduced FC strength (FCS) to DMN and FPN and increased FCS to VIS, while increased FCS was found in the MCI group between V_pcu and VIS. Significant correlations were found between the DP_pcu local glucose metabolism and functional connections to DMN and VIS in the HC group, which was absent in the MCI group. For V_pcu, a positive correlation was found between glucose metabolism and FCS with VIS in the HC group, while a negative correlation was shown in the MCI group. Moreover, the FCs between DP_pcu and FPN and VIS were associated with subject cognitive function. These findings shed light on our understandings about the functional-metabolic signal changes in the subregions of PCu in MCI using an integrated PET/fMRI imaging approach.