How does auditory cortex respond to silence? In this issue of Neuron, show that activity in macaque auditory cortex is highly structured even in the absence of sensory stimuli. These data reveal a close link between spontaneous neural activity and the functional organization of auditory cortex.
"For more details on the relationship between resting state fMRI and ongoing electrical activity in the high frequency range, see Nir et al. (2008); Schölvinck et al. (2010); Shmuel and Leopold (2008) and Leopold and Maier (2012) for recent reviews. The relationship between electrical activity across frequency bands, namely " cross-frequency, phase-amplitude coupling " and the behavioral relevance of the electrical signal in individual frequency bands has been discussed in details elsewhere (Belluscio et al., 2012; Canolty and Knight, 2010; Raichle, 2011; Schroeder and Lakatos, 2012) and is not further considered here. "
[Show abstract][Hide abstract] ABSTRACT: Brain structures do not work in isolation; they work in concert to produce sensory perception, motivation and behavior. Systems-level network activity can be investigated by resting state magnetic resonance imaging (rsMRI), an emerging neuroimaging technique that assesses the synchrony of the brain's ongoing spontaneous activity. Converging evidence reveals that rsMRI is able to consistently identify distinct spatiotemporal patterns of large-scale brain networks. Dysregulation within and between these networks has been implicated in a number of neurodegenerative and neuropsychiatric disorders, including Alzheimer's disease and drug addiction. Despite wide application of this approach in systems neuroscience, the physiological basis of these fluctuations remains incompletely understood. Here we review physiological studies in electrical, metabolic and hemodynamic fluctuations that are most pertinent to the rsMRI signal. We also review recent applications to neuropharmacology - specifically drug effects on resting state fluctuations. We speculate that the mechanisms governing spontaneous fluctuations in regional oxygenation availability likely give rise to the observed rsMRI signal. We conclude by identifying several open questions surrounding this technique.
[Show abstract][Hide abstract] ABSTRACT: Natural acoustic stimuli contain slow temporal fluctuations, and the modulation of ongoing slow-wave activity by bottom-up and top-down factors plays essential roles in auditory cortical processing. However, the spatiotemporal pattern of intrinsic slow-wave activity across the auditory cortical modality is unknown. Using in vivo voltage-sensitive dye imaging in anesthetized guinea pigs, we measured spectral tuning to acoustic stimuli across several core and belt auditory cortical areas, and then recorded spontaneous activity across this defined network. We found that phase coherence in spontaneous slow-wave (delta-theta band) activity was highest between regions of core and belt areas that had similar frequency tuning, even if they were distant. Further, core and belt regions with high phase coherence were phase shifted. Interestingly, phase shifts observed during spontaneous activity paralleled latency differences for evoked activity. Our findings suggest that the circuits underlying this intrinsic source of slow-wave activity support coordinated changes in excitability between functionally matched but distributed regions of the auditory cortical network.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 02/2013; 33(8):3299-310. DOI:10.1523/JNEUROSCI.5079-12.2013 · 6.34 Impact Factor
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