In humans, functional connectivity has been studied across a broad range of spatial and temporal scales. Using neuroimaging, functional connectivity has been studied using PET, near-infrared spectroscopy, and fMRI. With these methods, variability has been correlated across subjects, runs, blocks, trials, or individual blood-oxygen-level dependence (BOLD) time points and has been studied both during resting and task conditions, an ambiguity which can become confusing (Horwitz, 2003; Rogers et al., 2007). It is yet unclear if functional connectivity assessed in these various ways reflects similar phenomena (Fox & Raichle, 2007), but it is clear that these inter-regional interactions play a critical role in behavior and disease.
