, 2008). Electrodes on the cortical surface in these ECoG studies may prominently reflect processing in supragranular and granular cortical layers (Fukushima et al., 2012; Kajikawa and Schroeder, 2011). In comparison, intracerebral LFP recordings with higher-impedance electrodes in monkeys have higher spatial resolution (e.g., Katzner et al., 2009) and can reflect superficial or deep cortical layers (or a subcortical

area) depending on the electrode depth. There is evidence that neurons in different cortical check details layers may predominantly operate in different frequency bands. For example, gamma oscillations have been associated with superficial layers, while lower frequency oscillations have been found in deep layers (Buffalo et al., 2011; Maier et al., 2010; but see Lakatos et al., 2005, 2008). Thus, compared with methods used in animal studies, human electrophysiological techniques may not be as sensitive to low-frequency oscillations in deep cortical layers, although the effects of volume conduction and cortical folding complicate the interpretation of cortical surface recordings. Nir et al. (2008) also performed depth electrode recordings from auditory cortex in both hemispheres and showed a predominant contribution of gamma oscillations to BOLD connectivity. This predominance of gamma over lower frequencies may be due to auditory networks selleck chemicals llc operating at different frequencies to visual networks, their intracranial

recordings targeting particular cortical layers, or the possibility that cross-hemispheric interactions between homologous areas are more likely to involve gamma oscillations than intrahemispheric interactions (Engel et al.,

1991; Sil’kis and Bogdanova, 1998). Although these ECoG studies reported the strongest interareal correlations in gamma power, there were also significant correlations in the power of lower-frequency oscillations (1–25 Hz) between areas. Given this synchronization of low-frequency oscillations between brain areas, cross-frequency coupling between the low and gamma frequencies in the individual areas may have contributed to the reported interareal correlations in gamma power. There is evidence for prominent low-frequency oscillatory contributions to BOLD connectivity in a recent electroencephalography study using electrodes not on the intact dura of anesthetized rats (Lu et al., 2007). This study demonstrated that delta oscillations (1–4 Hz) contributed to BOLD connectivity between bilateral primary somatosensory cortices during anesthesia. However, it is not clear how much delta oscillations normally contribute to BOLD connectivity, because anesthetic agents generally alter neural activity and hemodynamics, including shifts in relative power from higher-frequency neural activity to delta oscillations (Franks, 2008; Williams et al., 2010). Delta oscillations have been reported to have an organizing influence on sensory processing in behaving monkeys through hierarchical coupling (Lakatos et al.