Cortical network functional connectivity in the descent to sleep

Department of Radiology, Washington University School of Medicine, 4525 Scott Avenue, St. Louis, MO 63110, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 04/2009; 106(11):4489-94. DOI: 10.1073/pnas.0900924106
Source: PubMed


Descent into sleep is accompanied by disengagement of the conscious brain from the external world. It follows that this process should be associated with reduced neural activity in regions of the brain known to mediate interaction with the environment. We examined blood oxygen dependent (BOLD) signal functional connectivity using conventional seed-based analyses in 3 primary sensory and 3 association networks as normal young adults transitioned from wakefulness to light sleep while lying immobile in the bore of a magnetic resonance imaging scanner. Functional connectivity was maintained in each network throughout all examined states of arousal. Indeed, correlations within the dorsal attention network modestly but significantly increased during light sleep compared to wakefulness. Moreover, our data suggest that neuronally mediated BOLD signal variance generally increases in light sleep. These results do not support the view that ongoing BOLD fluctuations primarily reflect unconstrained cognition. Rather, accumulating evidence supports the hypothesis that spontaneous BOLD fluctuations reflect processes that maintain the integrity of functional systems in the brain.

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    • "It has been suggested that the variety of spontaneous activity patterns that the brain enters during task-free conditions reflects the naturally itinerant and variegated quality of normal consciousness [Raichle, 2011]. However, spatio-temporal patterns of resting state activity are globally well preserved in states such as sleep [Boly et al., 2009, 2012; Brodbeck et al., 2012; Larson-Prior et al., 2009; Tagliazucchi et al., 2013a,b,c] in which there is a reduced level of awareness—although very specific changes in connectivity occur across NREM sleep, allowing the decoding of the sleep stage from fMRI data [Tagliazucchi et al., 2012c; Tagliazucchi and Laufs, 2014]. Thus, if the subjective quality of consciousness is markedly different in deep sleep relative to the normal wakeful state (for example) yet FC measures remain largely preserved, this would suggest that these measures provide limited information about the biological mechanisms underlying different conscious states. "
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    • "These changes in local neural activity within a sleep stage play an essential but not exclusive role in functions of sleep such as memory maintenance and homeostasis; modulation of functional interactions among brain regions is also needed (Diekelmann and Born, 2010; Tononi and Cirelli, 2006). In fact, previous human neuroimaging studies compared functional connectivity patterns between wakefulness and sleep periods such as NREM sleep (Andrade et al., 2011; Horovitz et al., 2009; Koike et al., 2011; Sämann et al., 2011; Spoormaker et al., 2012), sleep stage 1 (Horovitz et al., 2008; Larson-Prior et al., 2009, 2011; Spoormaker et al., 2012; Uehara et al., 2013; van Dongen et al., 2011), SWS (Chow et al., 2013; Koike et al., 2011; Spoormaker et al., 2012), and REM sleep (Chow et al., 2013; Laureys et al., 2001; Maquet et al., 2000). Nevertheless, to compare the connectivity across different types of sleep stages, these neuroimaging studies implicitly assumed that functional connectivity was stable during a given sleep stage. "
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