Currently, the most popular neuroimaging approach for studying functional connectivity is using fMRI to examine inter-regional correlations across individual BOLD time-points (functional connectivity MRI, or fcMRI). Often, these correlations are examined during specific tasks and have been related to individual subject’s task performance (Ranganath et al., 2005; Hampson et al., 2006b), genetics (Pezawas et al., 2005), and even personality (Pezawas et al., 2005). However, a recent advance with important clinical applications has been the discovery of robust inter-regional correlations in spontaneous BOLD fluctuations present even in the absence of an assigned task, referred to as resting state functional connectivity (for review see (Fox & Raichle, 2007)). These spontaneous fluctuations are consistently correlated between regions with similar functional properties and known anatomical connections including somatomotor, visual, auditory, language, default mode, and corticothalamic networks (Fox & Raichle, 2007). For example, one can extract the spontaneous BOLD modulations from a region such as the left somatomotor cortex and compute the correlation between this extracted signal and all other brain regions to obtain a map of the human somatomotor system (Biswal et al., 1995)
