Ongoing physiological processes in the cerebral cortex

Section on Cognitive Neurophysiology and Imaging, Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, 49 Convent Dr. 1E-21, MSC 4400, Bethesda, MD 20892, USA.
NeuroImage (Impact Factor: 6.36). 10/2011; 62(4):2190-200. DOI: 10.1016/j.neuroimage.2011.10.059
Source: PubMed


Functional magnetic resonance imaging (fMRI) has revealed that the human brain undergoes prominent, regional hemodynamic fluctuations when a subject is at rest. These ongoing fluctuations exhibit distinct patterns of spatiotemporal synchronization that have been dubbed "resting state functional connectivity", and which currently serve as a principal tool to investigate neural networks in the normal and pathological human brain. Despite the wide application of this approach in human neuroscience, the neural mechanisms that give rise to spontaneous fMRI correlations are largely unknown. Here we review results of recent electrophysiological studies in the cerebral cortex of humans and nonhuman primates that link neural activity to ongoing fMRI fluctuations. We begin by describing results obtained with simultaneous fMRI and electrophysiological measurements that allow for the identification of direct neural correlates of resting state functional connectivity. We next highlight experiments that investigate the correlational structure of spontaneous neural signals, including the spatial variation of signal coherence over the cortical surface, across cortical laminae, and between the two hemispheres. In the final section we speculate on the origins and potential consequences of ongoing signals for normal brain function, and point out inherent limitations of the fMRI correlation approach.

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Available from: Alexander Maier, Feb 24, 2014
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    • "However, the global perfusion signal will likely contain neuronal contributions (Leopold and Maier, 2012; Murphy et al., 2009), and regressing out the global signal will likely bias the perfusion time series just as it biases the BOLD time series and connectivity measures. Thus, the use of global signal regression is a controversial issue in functional connectivity calculations (Saad et al., 2013). "
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    Brain Connectivity 06/2015; DOI:10.1089/brain.2015.0344
    • "To date, studies of the neural correlates involved with spontaneous BOLD activity have used electrophysiological recording methods such as the electroencephalography (EEG), electrocorticography (ECoG), local field potential (LFP), and multi-unit activity (MUA) (Leopold and Maier 2012). Leopold and his colleagues have demonstrated that spontaneous BOLD fluctuations correlate with slow modulation of the spiking rate, MUA power, and LFP power (gamma band and 2–15 Hz range) in the monkey visual cortex at rest (Shmuel and Leopold 2008; Scholvinck et al. 2010). "
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    Brain Structure and Function 06/2015; DOI:10.1007/s00429-015-1073-0 · 5.62 Impact Factor
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    • "Resting-state functional MRI (RS-fMRI) is particularly well-suited to explore anesthesia-related changes as it allows for the noninvasive assessment of whole brain functional interactions in the absence of any explicit task. The spontaneous, low-frequency (0.01–0.1 Hz) blood oxygenation level-dependent (BOLD) signals recorded with the technique have been shown to reflect (at least partially) the underlying neuronal activity [Shmuel and Leopold, 2008; for reviews, see Fox and Raichle 2007, Leopold and Maier 2012 and importantly, evaluation of their temporal dependencies have revealed robust and reliable connectivity maps [e.g., Biswal et al., 1995; Beckmann et al., 2005; Damoiseaux et al., 2006; for review, see Fox and Raichle, 2007] across multiple species [e.g., Hutchison et al., 2010, 2011; Kannurpatti et al., 2008; Liang et al., 2011; Pawela et al., 2008; Vincent et al., 2007; for review see Hutchison and Everling, 2012]. The technique can serve to extend positron emission tomography (PET) investigations that have provided critical findings related to anesthesia's metabolic effects [e.g., Alkire et al., 1997, 1999]. "
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