The parahippocampal gyrus links the default-mode cortical network with the medial temporal lobe memory system

Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, Massachusetts.
Human Brain Mapping (Impact Factor: 5.97). 03/2014; 35(3). DOI: 10.1002/hbm.22234
Source: PubMed


The default-mode network (DMN) is a distributed functional-anatomic network implicated in supporting memory. Current resting-state functional connectivity studies in humans remain divided on the exact involvement of medial temporal lobe (MTL) in this network at rest. Notably, it is unclear to what extent the MTL regions involved in successful memory encoding are connected to the cortical nodes of the DMN during resting state. Our findings using functional connectivity MRI analyses of resting-state data indicate that the parahippocampal gyrus (PHG) is the primary hub of the DMN in the MTL during resting state. Also, connectivity of the PHG is distinct from connectivity of hippocampal regions identified by an associative memory-encoding task. We confirmed that several hippocampal encoding regions lack significant functional connectivity with cortical DMN nodes during resting state. Additionally, a mediation analysis showed that resting-state connectivity between the hippocampus and posterior cingulate cortex-a major hub of the DMN-is indirect and mediated by the PHG. Our findings support the hypothesis that the MTL memory system represents a functional subnetwork that relates to the cortical nodes of the DMN through parahippocampal functional connections. Hum Brain Mapp, 2013. © 2013 Wiley Periodicals, Inc.

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Available from: Koene R.A. Van Dijk, Aug 07, 2015
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    • "Thus, it may be that impairment in switching hippocampal network engagement from resting functional connectivity state to task-based functional connectivity state recruiting memory-relevant regions underlies the apparent disengagement results described in the present study. Dynamic connectivity of hippocampal complex regions and DMN mediated by behavior has also been reported in other studies not specifically interested in APOE [McLaren et al., 2014; Ward et al., 2014]. "
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    Full-text · Article · Oct 2015 · Human Brain Mapping
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    • "ual basis . To achieve this , the reconstruction parameters were interactively set according to the neuroanatomy of each subjects , until the known anatomy of the DMN was retrieved ( i . e . , functional connectivity in the medial prefrontal cortex ( mPFC ) , the PCC / precuneus , the left and right temporoparietal lobes , Buckner et al . , 2008 ; Ward et al . , 2014 ) . The difference and percentage ( % ) change of each parameter were then computed , defined as follows : ( x - y ) for the difference and ( ( x − y ) / y × 100 ) for the % change , where x represents the subject - specific parameters and y the reference parameters extracted from S6 ."
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    • "Similar to the findings from Xu et al. (2009), these studies documented functional alterations of DMN areas in ε4 carriers compared to non-carriers. These areas are highly interconnected and belong to critical nodes of the DMN, involved in episodic memory (for review, see Buckner et al. 2008; Ward et al. 2014). Finally, one study with a large number of participants (n=132) reported no BOLD differences between ε4 carriers and non-carriers during encoding of line drawings (Johnson et al. 2006). "
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