The meaning and function of this low-frequency signal is unclear (Raichle, 2010), but rs-fcMRI fluctuations have been linked, in part, to fluctuations in gamma- (<4Hz) and delta-band (30–100Hz) spectral power, as well as to slow cortical potentials (He et al., 2008; Lu et al., 2007; Raichle, 2010; Scholvinck et al., 2010). These correlations can occur in the absence of direct anatomical connections (e.g., between bilateral non-foveal V1 regions in macaques (Vincent et al., 2007)), and therefore represent something beyond monosynaptic connectivity, though they are of course constrained by the physical structure of the neural network (Johnston et al., 2008). The fact that functionally related regions often exhibit correlated rs-fcMRI signal, even in the absence of direct structural connectivity, has led to a hypothesis that rs-fcMRI signal correlations reflect histories of coactivation between brain regions (Dosenbach et al., 2007; Fair et al., 2007a; Kelly et al., 2009). Recent work has shown that distinctions between brain regions made in rs-fcMRI networks are reflected in distinct evoked fMRI task responses (Dosenbach et al., 2007; Nelson et al., 2010), and that visual perceptual learning
