Hippocampus-precuneus functional connectivity as an early sign of Alzheimer's disease: a preliminary study using structural and functional magnetic resonance imaging data.

Alzheimer's disease (AD) is characterized by structural atrophies in the hippocampus (HP) and aberrant patterns of functional connectivities (FC) between the hippocampus and the rest of the brain. However, the relationship between cortical atrophy levels and corresponding degrees of aberrant FC patterns has not been systematically examined. In this study, we investigated whether there was an explicit link between structural abnormalities and corresponding functional aberrances associated with AD using structural and functional magnetic resonance imaging (fMRI) data. To this end, brain regions with cortical atrophies that are associated with AD were identified in the HP in the left (L) and right (R) hemispheres using structural MRI data from volume analyses (p<0.03 for L-HP; p<0.04 for R-HP) and voxel-based morphometry analyses (p<4×10(-4) for L-HP; p<2×10(-3) for R-HP). Aberrantly reduced FC levels between the HP (with atrophy) and precuneus were also consistently observed in fMRI data from AD than HC brains that were analyzed by the Pearson's correlation coefficients (p<3×10(-4) for L-HP; and p<8×10(-5) for R-HP). In addition, the substantial negative FC levels from the HC brains between the precuneus and post central gyrus (PoCG) without structural atrophy were also significantly diminished from the AD brains (p<5×10(-5) for L-PoCG; and p<6×10(-5) for R-PoCG). The effect sizes of these aberrant FC levels associated with AD were greater than that of cortical atrophy levels when comparing using normalized Z score and Cohen's d measures, which indicates that an aberrant FC level may precede cortical atrophy.