Brain Intrinsic Functional Activity in Relation to Metabolic Changes in Alzheimer's Disease: A Simultaneous PET/fMRI...

Previous studies have shown that the intrinsic brain functional activity significantly reduced in a variety of regions of Alzheimer's disease (AD) patients. However, the associated underlying metabolic mechanism remains not clear. Brain activity is primarily driven by the dynamic activity of neurons and their interconnections, which are regulated by synapses and are closely related to glucose uptakes. Simultaneous FDG-PET/fMRI imaging provides a unique opportunity to measure the concurrent brain functional activity and cerebral glucose metabolism information. In this study, using simultaneous resting-state PET/fMRI imaging, we investigated the concurrent global intrinsic activity and metabolic signal changes in AD patients. Twenty-two controls and nineteen AD patients were included. We compared the whole-brain amplitude of low frequency fluctuations (ALFF) measured using fMRI imaging and glucose uptake maps acquired from PET imaging between the two groups. Both maps showed significant reductions in the precuneus and left inferior parietal lobule (IPL) in AD compared to the control groups. Moreover, the ALFF within the precuneus and left IPL were significantly correlated with the colocalized glucose metabolism. The ALFF in the left IPL was significantly correlated with patient cognitive performance evaluated using MMSE or MoCA. Our findings provide useful insights into the understanding of brain intrinsic functional-metabolic activity and its role in AD pathology.