Figure 1
Brain measures, models, and cohort. (a) Functional connectivity density (FCD) maps. A voxel-wise correlation matrix is computed from BOLD time courses and functional links are defined as above-threshold correlations. A voxel’s degree, defined as the number of its associated links, is a simple measure of centrality. We refer to the logarithm of degree (plus one) as FCD. (b) Multivariate cross-validated models. Subjects were assigned a label defined by a measure of cognitive/motor decline after correcting for healthy age/sex expectations (fast vs slow decline, excluding intermediate subjects during training), or by genetics (pre-HD vs control). Subjects from three of the four imaging sites (all but one) were included in the model training set. Performance of the model was estimated on subjects from the remaining site, and the process was iterated for every site (leave-one-site-out cross-validation, LOSO-CV). Test-site validation was quantified by the area under the receiver operating characteristic (ROC) curve (AUC). Additionally, for cognitive stratification, the Spearman rank correlation of the continuous output of classifiers vs cognitive decline rates was estimated using all subjects from test sites. (c) Patient cohort. Participants belonged to the Track-On HD study. Two rs-fMRI samples were used per subject. Longitudinal change in performance on 10 cognitive and motor tests was evaluated, including measurements from the immediately preceding TRACK-HD study.
