Extracting low-frequency fluctuations in a single subject's preprocessed task-free functional magnetic resonance imaging (TF-fMRI) data within a series of seeds to be used in graph theoretical analyses. (Top left) One of 100 representative volumes of a subject's preprocessed TF-fMRI data. (Top right) Time series from a collection of seed regions (also known as nodes in graph theoretical terms) demonstrating the typical low-frequency fluctuations in the blood oxygen level-dependent (BOLD) signal within each seed. (Bottom) Connectivity matrix (for example, adjacency, correlation, partial correlation, or covariance matrix) encoding the relationship between the signal within each seed to every other seed. This connectivity matrix can then be subjected to graph theoretical analyses. ROI, region of interest; RS-fMRI, resting-state functional magnetic resonance imaging.