Article

Coherent Spontaneous Activity Identifies a Hippocampal-Parietal Memory Network

Mallinckrodt Institute of Radiology, and Department of Neurology, Washington University School of Medicine, 4525 Scott Avenue, St. Louis, MO 63110, USA.
Journal of Neurophysiology (Impact Factor: 2.89). 01/2007; 96(6):3517-31. DOI: 10.1152/jn.00048.2006
Source: PubMed

ABSTRACT

Despite traditional theories emphasizing parietal contributions to spatial attention and sensory-motor integration, functional MRI (fMRI) experiments in normal subjects suggest that specific regions within parietal cortex may also participate in episodic memory. Here we examined correlations in spontaneous blood-oxygenation-level-dependent (BOLD) signal fluctuations in a resting state to identify the network associated with the hippocampal formation (HF) and determine whether parietal regions were elements of that network. In the absence of task, stimuli, or explicit mnemonic demands, robust correlations were observed between activity in the HF and several parietal regions (including precuneus, posterior cingulate, retrosplenial cortex, and bilateral inferior parietal lobule). These HF-correlated regions in parietal cortex were spatially distinct from those correlated with the motion-sensitive MT+ complex. Reanalysis of event-related fMRI studies of recognition memory showed that the regions spontaneously correlated with the HF (but not MT+) were also modulated during directed recollection. These regions showed greater activity to successfully recollected items as compared with other trial types. Together, these results associate specific regions of parietal cortex that are sensitive to successful recollection with the HF.

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Available from: Justin L Vincent
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    • "Beginning with observations byBiswal et al. (1995), empirical studies of spontaneous BOLD fMRI have revealed spatial covariance across cortical and subcortical structures that often conforms to previously established functional brain networks. For example, rsfMRI signal covariance can be used to parcellate sensorimotor systems (van DenHeuvel and Hulshoff Pol, 2010;Asemi et al., 2015), higher order associative fronto-parietal networks (Vincent et al., 2006Vincent et al., , 2008), thalamic nuclei (Zhang et al., 2008;Fan et al., 2015), and cerebellar cortex (Buckner et al., 2011). In particular, studies quantifying correlational structures in spontaneous BOLD signals during non-task " resting states " have grown exponentially over the past 20 years, resulting in detailed parcellations of functionally separated cortical networks in the human brain (e.g.,Yeo et al., 2011;Power et al., 2014). "

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    • "Further, there is good reason to think that our algorithm will prove useful in these other domains. Similar to the somatomotor system, language and memory systems have been mapped using spontaneous activity recorded with fMRI (McCormick et al., 2013; Tie et al., 2014; Vincent et al., 2006). There is no reason to think that incorporation of spontaneous activity into preoperative mapping will be any less useful for these other systems. "
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    • "Connectional anatomy in nonhuman primates indicates that MTL structures have both afferent and efferent projections to specific posteriomedial, temporal, parietal, and medial frontal regions that are estimated to be components of the DN [Kobayashi and Amaral, 2003, 2007; Lavenex et al., 2004]. However, functional connectivity studies repeatedly find that coupling between the MTL and cortical DN regions is relatively weak as compared with corticocortical coupling, although regions within the DN are the most strongly coupled regions when the MTL itself is the initiating point for fcMRI analysis [Kahn et al., 2008; r Mueller et al. r r 12 r Vincent et al., 2006]. Conventional graph theoretical representations of the DN have suggested that MTL structures form a separated sub-unit with rather weak connections to certain other DN nodes, at least insofar as its relative coupling strength compared with cortical regions of the DN [Andrews-Hanna et al., 2010; Buckner et al., 2008]. "
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