The purpose of this study was to investigate the decline of recent memory performance with amyloid PET and a surrogate maker of cognitive reserve in cognitively normal elderly people and amyloid positive patients with amnestic mild cognitive impairment (MCI).
Subjects selected from in-house studies were 61 cognitively normal (CN) subjects (age: 69.8±5.7 (60-82) y.o., years of school education (YSE): 12.2±2.4 (9-18) years) and amyloid positive 17 patients with MCI (age: 74.6±6.1 (60-82) y.o.; YSE: 11.4±2.6 (8-16) years). They underwent a test of logical memory-II (LM-II) of Wechsler memory scale revised. Distribution volume ratio (DVR) image was calculated from dynamic PiB PET using simplified reference tissue mode 2. The DVR images spatially normalized using DARTEL method. Statistical analyses of the DVR images were performed with SPM8 for multiple regressions to assess the relationship with memory, age, and YSE. Correlation and regression analyses among regional DVR value, age, LM-II score and YSE were performed using SPSS.
Eleven out of 61 cases of CN were visually evaluated as amyloid-positive scan. LM-II score was 16.8 ± 6 (4-35) and 4.4±4.8 (0-15) in CN and MCI, respectively. A SPM analysis of the group of CN demonstrated that LM-II score was inversely associated with DVR values in the bilateral localized medial temporal cortices (p<0.005, ext>50). In CN a significant correlation was observed between LM-II and YSE (r>0.5, p<0.001). Multiple regression analyses with LM-II as a dependent variable represented that statistically significant terms were YSE (p<0.001) and an interaction term of YSE and regional DVR in the medial temporal lobe. In contrast, the combination group of CN and amyloid positive MCI showed an inverse association between DVR value and LM-II in wider areas such as anterior and posterior cingulate area, lateral temporal lobes, and basal forebrain in a SPM analysis (p<0.005, ext>50).
The results suggest that, recent memory declines in association with amyloid deposition in the medial temporal lobe and cognitive reserve at cognitively normal stage, while recent memory performance goes down along with amyloid deposition spreading widely at the stage of cognitively normal to MCI in AD continuum.
© 2017 Published by Elsevier Inc.