LATE-LIFE ACCELERATED DECREASE IN REGIONAL METABOLIC ACTIVITY AND ITS IMPACT ON COGNITIVE DECLINE: A LONGITUDINAL FDG-PET STUDY

Abstract

Cerebral glucose metabolic activity decreases with advancing age. This trend has been consistently observed even in the cognitively normal elderly individuals. Previous studies using 18 fluoro-2-deoxyglucose positron emission topography (FDG-PET), however, were mostly cross-sectional in design, and were thus incapable of depicting the true trajectories of change. Hence we herein conducted a longitudinal PET study, purporting to identify brain regions that exhibit aging-related metabolic change that are observed in follow-ups. Furthermore, since quadratic relationship between age and regional metabolism were reported, we investigated if the magnitude of change varies with age. Lastly, we also examined whether this metabolic trajectory predicts memory decline. Right-handed 63 cognitively normal old adults (aged 57–81, mean 68.84(4.60)) were included in this research. Participants underwent both PET scans and neuropsychological tests at the baseline year and were followed for approximately four years. To find regions that show longitudinal metabolic reduction, preprocessing and paired T test were done with SPM12 (p<.05 FWE corrected). Next, individual metabolic uptake values of each year were extracted and pons-normalized via PickAtlas. Lme4 package in R studio was then used to examine if the rate of decline interacts with age. Finally, multiple linear regression analysis was performed assessing the correlated changes of metabolism and memory. Figure 1 portrays the result of paired T test. Massive metabolic reduction was found in middle frontal gyrus (MFG) and medial orbitofrontal cortex. Middle temporal gyrus (MTG), insula, thalamus and posterior cingulate cortex also deteriorated with aging. In particular, the rates of metabolic decline in MFG and MTG interacted with age, demonstrating late-life accelerated degradation. Moreover, the magnitude of each decline was significantly correlated with memory decline.