A cartoon illustration of independent component analysis (ICA) on fMRI time courses, which are assumed to be comprised of linearly mixed sources. Spatial extent of statistically independent components (such as IC1 and IC2 in this example) which represent two sources (which can represent spatially independent brain networks), and their representative time courses for each source, can be extracted with ICA from a (linear) mix of the sources, the overall spatial extent of which is shown on the left (Calhoun, Liu, et al., 2009). Note that, as in this example, the sources do not have to be spatially clustered for ICA to extract them