Within-patient correspondence of amyloid-ß and intrinsic network connectivity in Alzheimer's disease.

ABSTRACT

There is striking overlap between the spatial distribution of amyloid-ß pathology in patients with Alzheimer's disease and the spatial distribution of high intrinsic functional connectivity in healthy persons. This overlap suggests a mechanistic link between amyloid-ß and intrinsic connectivity, and indeed there is evidence in patients for the detrimental effects of amyloid-ß plaque accumulation on intrinsic connectivity in areas of high connectivity in heteromodal hubs, and particularly in the default mode network. However, the observed spatial extent of amyloid-ß exceeds these tightly circumscribed areas, suggesting that previous studies may have underestimated the negative impact of amyloid-ß on intrinsic connectivity. We hypothesized that the known positive baseline correlation between patterns of amyloid-ß and intrinsic connectivity may mask the larger extent of the negative effects of amyloid-ß on connectivity. Crucially, a test of this hypothesis requires the within-patient comparison of intrinsic connectivity and amyloid-ß distributions. Here we compared spatial patterns of amyloid-ß-plaques (measured by Pittsburgh compound B positron emission tomography) and intrinsic functional connectivity (measured by resting-state functional magnetic resonance imaging) in patients with prodromal Alzheimer's disease via spatial correlations in intrinsic networks covering fronto-parietal heteromodal cortices. At the global network level, we found that amyloid-ß and intrinsic connectivity patterns were positively correlated in the default mode and several fronto-parietal attention networks, confirming that amyloid-ß aggregates in areas of high intrinsic connectivity on a within-network basis. Further, we saw an internetwork gradient of the magnitude of correlation that depended on network plaque-load. After accounting for this globally positive correlation, local amyloid-ß-plaque concentration in regions of high connectivity co-varied negatively with intrinsic connectivity, indicating that amyloid-ß pathology adversely reduces connectivity anywhere in an affected network as a function of local amyloid-ß-plaque concentration. The local negative association between amyloid-ß and intrinsic connectivity was much more pronounced than conventional group comparisons of intrinsic connectivity would suggest. Our findings indicate that the negative impact of amyloid-ß on intrinsic connectivity in heteromodal networks is underestimated by conventional analyses. Moreover, our results provide first within-patient evidence for correspondent patterns of amyloid-ß and intrinsic connectivity, with the distribution of amyloid-ß pathology following functional connectivity gradients within and across intrinsic networks.