Longitudinal effects of estrogen replacement therapy on PET cerebral bloodflow and cognition

Observational studies suggest that estrogen replacement therapy (ERT) may p rotect against age-related memory decline and lower the risk of Alzheimer's disease (AD). This study aimed to characterize the neural substrates of th ose effects by comparing 2-year longitudinal changes in regional cerebral b lood flow (rCBF) in 12 ERT users and 16 nonusers. Positron emission tomogra phy (PET) measurements of rCBF were obtained under three conditions: rest, and verbal and figural recognition memory tasks. Groups showed different pa tterns of change in rCBF over time in a number of brain areas. These group differences, for the most part, reflected regions of increased rCBF over ti me in users compared to nonusers. The greatest differences between ERT user s and nonusers were in the hippocampus, parahippocampal gyrus, and temporal lobe, regions that form a memory circuit and that are sensitive to preclin ical AD. Across a battery of standardized neuropsychological tests of memor y, users obtained higher scores than did nonusers of comparable intellect. Group differences in longitudinal change in rCBF patterns may reflect one w ay through which hormones modulate brain activity and contribute to enhance d memory performance among ERT users. (C) 2000 Published by Elsevier Scienc e Inc. All rights reserved.