Sheldon FC, Petrella JR, Doraiswamy P.
Voxel degree as a measure of functional connectivity changes in Alzheimer's disease.
Human Amyloid Imaging 2011 Meeting Abstracts. 2011 Jan 15;
The causes underlying the pattern of amyloid deposition in the Alzheimer's brain are not well understood. It has
been shown that amyloid distribution in Alzheimer's disease (AD) overlaps that of major brain network hubs in
healthy individuals, implying a relationship between the brainfs underlying network architecture and the pattern
of amyloid deposition. It remains unclear how the brainfs hub architecture evolves over the progression of AD as
amyloid deposition ensues. In this study, we examine the brainfs functional network architecture using fcMRI to
determine its evolution over the progression of AD. 13 patients with mild AD, 11 patients with prodromal AD (pAD),
23 patients with stable mild cognitive impairment (sMCI), and 28 elderly controls (ONS) underwent functional MR
imaging during a face-name associative encoding task. Images were normalized to a standardized brain template
(Montreal Neurologic Institute) using statistical parametric mapping software (SPM 5) and masked to include only
grey matter. Pair-wise correlations were calculated and summed for every remaining voxel to obtain an estimate
of that voxelfs weighted degree. These edegree mapsf were normalized to z-scores in each individual. To assess
group differences, a edisease rankf of 1-4 was assigned for patients in, respectively, AD, pAD, sMCI, and ONS.
This rank was then used in a voxel-wise correlation with the weighted connectivity to identify areas which showed
functional disruption along with the progression of AD. A cluster in the right inferior gyrus showed significant
functional disruption along with disease. Mean values of connectivity (z-scored) were found to be 0.75 (ONS),
0.60 (sMCI), 0.27 (pAD), and 0.04 (AD). As tissue classification schemes improve, it may be possible to extend
these methods to measures of nonlinear connectivity which may then give us deeper insight into the pathological
changes that parallel disease.