Distinct Functional and Metabolic Alterations of DMN Subsystems in Alzheimer's Disease: A Simultaneous FDG-PET/fMRI Study.

The default mode network (DMN) dysfunction has been widely identified in Alzheimer's disease (AD). Increasing evidence has shown that the functional heterogeneity of DMN has been associated with distinct cognitive functions. The pathophysiological changes of these two DMN subsystems, i.e., anterior DMN (aDMN) and posterior DMN (pDMN), also showed different patterns in the AD patients. Yet the underlying metabolic mechanism remains not clear. In this work, we performed a simultaneous FDG-PET/fMRI study, to investigate the distinct functional and metabolic alterations of DMN subsystems in AD. Significantly decreased functional connectivity strength (FCS) in pDMN but not aDMN was found in AD patients. The retaining connectivity in aDMN might represent a compensatory strategy. Concurrently, significant glucose hypometabolism was shown in pDMN and aDMN of AD patients, respectively. Moreover, the reduction of FCS in pDMN was positively correlated with MMSE score of patients. Our study suggests that resting state functional connectivity and glucose metabolism changed differently in the aDMN and pDMN of AD. Our findings brought new insights in understanding the underlying metabolism changes along with functional alterations in AD.