Abstract
Resting state functional MRI (R-fMRI) studies have shown that slow (<0.1Hz), intrinsic fluctuations of the blood oxygen level dependent (BOLD) signal are temporally correlated within hierarchically organized functional systems known as resting state networks (RSNs) (Doucet et al., 2011). Most broadly, this hierarchy exhibits a dichotomy between two opposed systems (Fox et al., 2005). One system engages with the environment and includes the visual, auditory, and sensorimotor (SMN) networks as well as the dorsal attention network (DAN), which controls spatial attention. The other system includes the default mode network (DMN) and the fronto-parietal control system (FPC), RSNs that instantiate episodic memory and executive control, respectively. Here, we test the hypothesis, based on the spectral specificity of electrophysiologic responses to perceptual vs. memory tasks (Klimesch, 1999; Pfurtscheller and Lopes da Silva, 1999), that these two large-scale neural systems also manifest frequency specificity in the resting state. We measured the spatial correspondence between electrocorticographic (ECoG) band-limited power (BLP) and R-fMRI correlation patterns in awake, resting, human subjects. Our results show that, while gamma BLP correspondence was common throughout the brain, theta (4–8Hz) BLP correspondence was stronger in the DMN and FPC, whereas alpha (8–12Hz) correspondence was stronger in the SMN and DAN. Thus, the human brain, at rest, exhibits frequency specific electrophysiology, respecting both the spectral structure of task responses and the hierarchical organization of RSNs.
Highlights
Intrinsic brain activity has emerged as a major focus of systems neuroscience research (Raichle, 2009)
Surface-to-electrode blood oxygen level dependent (BOLD) signal resampling was computed according to the expected electrophysiologic contribution of each surface locus modeled as a transcortical dipole
ECoG signals were referenced to the common mean and band-pass filtered at logarithmic intervals to isolate particular carrier frequencies; these band-limited signals were squared and filtered to isolate specific modulation frequencies of the band-limited power (BLP) signal derived from a given carrier frequency band
Summary
Intrinsic brain activity has emerged as a major focus of systems neuroscience research (Raichle, 2009). I.e., task-free, functional magnetic resonance imaging (R-fMRI) currently is the primary technique used in the investigation of intrinsic brain activity (Smith et al, 2013). On the basis of R-fMRI studies, it is established that slow ( < 0.1 Hz), intrinsic fluctuations of the blood oxygen level dependent (BOLD) signal are temporally correlated within spatially distributed functional systems. This phenomenon is widely known as functional connectivity. The associated topographies are known as resting state networks (RSNs) or, equivalently, intrinsic connectivity networks (ICNs) (Zielinski et al, 2010). The RSN hierarchy splits at the highest level into two "systems," originally referred to as "task positive" vs
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