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Tau Protein is Associated with Longitudinal Memory Decline in Cognitively Healthy Subjects with Normal Alzheimer's Disease Cerebrospinal Fluid Biomarker Levels.

BACKGROUND
We investigated a sample of cognitively healthy subjects with normal Alzheimer's disease (AD) cerebrospinal fluid (CSF) biomarker levels to identify the earliest variables related to longitudinal memory changes.


OBJECTIVE
Employing a new highly demanding learning and memory test (the Ancient Farming Equipment Test; AFE-T), we aimed to investigate whether a biomarker related to neurodegeneration (i.e., CSF tau) was associated with longitudinal memory decline.


METHODS
Thirty-two cognitively and biologically normal (CBN) subjects underwent MRI, neuropsychological assessment, and the AFE-T at baseline and 18 months later. To explore the relationship between cognitive performance and relevant factors, a linear model was set up. For a secondary analysis that further explore the effect of tau, the subjects were divided into CBN-Tau↓ (tau < 228.64 pg/ml; n = 16) and CBN-Tau↑ (tau > 228.64 pg/ml; n = 16). We also performed voxel-based morphometry (VBM) to identify regions of grey matter volume that would predict both baseline and longitudinal cognitive performance.


RESULTS
Our main finding was an association between CSF tau and longitudinal memory decline measured with AFE-T (B = -0.17, p < 0.05; r = -0.414; p < 0.01), and further analyses showed different evolvement between subgroups, with an accelerated decline in individuals with higher tau (F(1,31) = 8.37; p < 0.01). VBM results suggested that AFE-T performance is related to grey matter volume in a medial temporal, middle frontal, and posterior cerebellar network at baseline, and that there are strategic brain areas driving the longitudinal cognitive changes.


CONCLUSIONS
The present findings provide evidence for structural and biological markers linked to cognitive aging by highlighting the role of tau, a marker of neurodegeneration, which can be related with the earliest memory changes in healthy subjects.