Decoupling of Local Metabolic Activity and Functional Connectivity Links to Amyloid in Alzheimer’s Disease

Abstract

Background:

Both ongoing local metabolic activity (LMA) and corresponding functional connectivity (FC) with remote brain regions are progressively impaired in Alzheimer’s disease (AD), particularly in the posterior default mode network (pDMN); however, it is unknown how these impairments interact. It is well known that decreasing mean synaptic activity of a region, i.e., decreasing LMA, reduces the region’s sensitivity to afferent input from other regions, i.e., FC.

Objective:

We hypothesized progressive decoupling between LMA and FC in AD, which is linked to amyloid-β pathology (Aβ).

Methods:

Healthy adults (n=20) and Aβ+patients without memory impairment (n=9), early MCI (n=21), late MCI (n=18) and AD (n=22) were assessed by resting-state fMRI, FDG-PET, and AV-45-PET to measure FC, LMA, and Aβ of the pDMN. Coupling between LMA and FC (r_LA/FC) was estimated by voxelwise correlation.

Results:

R_LMA/FC decreased with disease severity (F=20.09, p<0.001). This decrease was specifically associated with pDMN Aβ (r=−0.273, p=0.029) but not global Aβ (r=−0.112, p=0.378) and with the impact of Aβ on FC (i.e., r_Aβ/FC, r=−0.339; p=0.006). In multiple regression models r_LMA/FC was also associated with memory impairment, reduced cognitive speed and flexibility, outperforming global Aβ, pDMN Aβ, pDMN LMA, and pDMN FC, respectively.

Conclusion:

Results demonstrate increasing decoupling of LMA from its FC in AD. Data suggest that decoupling is driven by local Aβ and contributes to memory decline.