For interactions in the beta band, these are located in dorsolateral prefrontal, lateral parietal, and temporal cortex (Figure 2E). In contrast, theta-band interactions involve major hubs in the medial temporal lobe, and gamma-band hubs can be observed in sensorimotor cortex (Hipp et al., 2012). An important finding is that coupling, as revealed by envelope correlations, can dissociate from the spatial distribution of local signal power. Another MEG study employing

a related approach has provided similar results (Brookes et al., 2012). A recent study of phase ICMs employing the phase lag index has revealed somewhat different patterns of highly connected regions that differ across frequency bands (Hillebrand et al., www.selleckchem.com/products/VX-770.html 2012). In the alpha band, the most strongly connected regions were visual and posterior cingulate cortex. In the beta band, this involved sensorimotor and parietal cortex, and in the gamma band, temporal and parietal areas showed high functional connectivity. Phase ICMs have also been mapped in a recent study that focused on coupling in the dorsal attention network (Marzetti et al., 2013). Significant delta- and alpha-band interactions were observed between homologous regions of the attention network in the left and right hemisphere. Moreover, this network showed coupling in the alpha band to visual regions, as well as beta-band interactions with sensorimotor regions. Taken Epigenetics inhibitor together, these

studies seem to provide evidence that phase ICMs can dissociate from also envelope ICMs, but further studies will be required to elaborate this in greater

detail. An important question is to what extent the neurophysiological signatures of ICMs match their MRI-based characterization. The relation between LFP and BOLD signals has been the subject of a number of studies. BOLD fluctuations seem to correlate best with the slow power envelope fluctuations observed for LFPs and MEG or EEG signals (Logothetis et al., 2001, Leopold et al., 2003, Nir et al., 2007 and He et al., 2008). In particular, this holds for the gamma band, but lower frequencies have also been found to be related to the BOLD signal (He et al., 2008, Magri et al., 2012 and Keller et al., 2013). This is supported by studies that have employed direct coregistration of ongoing EEG or LFPs with BOLD activity (Shmuel and Leopold, 2008, Schölvinck et al., 2010 and Tagliazucchi et al., 2012a). It has been suggested that slow changes in both BOLD signal and power envelopes of oscillatory signals, may reflect endogenous fluctuations of neuronal excitability, which occur in a coupled manner across different cortical and subcortical regions (Leopold et al., 2003 and Deco and Corbetta, 2011). Taken together, these studies provide evidence that BOLD coupling analyses primarily reveal envelope ICMs, thus converging with neurophysiological analyses of envelope correlations.