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.

Download full-text


Available from: Koene R.A. Van Dijk, Aug 07, 2015
  • Source
    • "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]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The hippocampal complex is affected early in Alzheimer's disease (AD). Increasingly, altered functional connectivity of the hippocampus is recognized as an important feature of preclinical AD. Carriers of the APOEɛ4 allele are at an increased risk for AD, which could lead to altered hippocampal connectivity even in healthy older adults. To test this hypothesis, we used a paired-associates memory task to examine differences in task-dependent functional connectivity of the anterior and posterior hippocampus in nondemented APOEɛ4 carriers (n = 34, 18F) and noncarriers (n = 46, 31F). We examined anterior and posterior portions of the hippocampus separately to test the theory that APOEɛ4-mediated differences would be more pronounced in the anterior region, which is affected earlier in the AD course. This study is the first to use a psychophysiological interaction approach to query the context-dependent connectivity of subregions of the hippocampus during a memory task in adults at increased genetic risk for AD. During encoding, APOEɛ4 carriers had lower functional connectivity change compared to baseline between the anterior hippocampus and right precuneus, anterior insula and cingulate cortex. During retrieval, bilateral supramarginal gyrus and right precuneus showed lower functional connectivity change with anterior hippocampus in carriers. Also during retrieval, carriers showed lower connectivity change in the posterior hippocampus with auditory cortex. In each case, APOEɛ4 carriers showed strong negative connectivity changes compared to noncarriers where positive connectivity change was measured. These differences may represent prodromal functional changes mediated in part by APOEɛ4 and are consistent with the anterior-to-posterior theory of AD progression in the hippocampus. Hum Brain Mapp, 2015. © 2015 Wiley Periodicals, Inc.
    Human Brain Mapping 10/2015; DOI:10.1002/hbm.23036 · 5.97 Impact Factor
  • Source
    • "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 ."
    [Show abstract] [Hide abstract]
    ABSTRACT: In the past decade, the fusion between diffusion magnetic resonance imaging (dMRI) and functional magnetic resonance imaging (fMRI) has opened the way for exploring structure-function relationships in vivo. As it stands, the common approach usually consists of analysing fMRI and dMRI datasets separately or using one to inform the other, such as using fMRI activation sites to reconstruct dMRI streamlines that interconnect them. Moreover, given the large inter-individual variability of the healthy human brain, it is possible that valuable information is lost when a fixed set of dMRI/fMRI analysis parameters such as threshold values are assumed constant across subjects. By allowing one to modify such parameters while viewing the results in real-time, one can begin to fully explore the sensitivity of structure-function relations and how they differ across brain areas and individuals. This is especially important when interpreting how structure-function relationships are altered in patients with neurological disorders, such as the presence of a tumor. In this study, we present and validate a novel approach to achieve this: First, we present an interactive method to generate and visualize tractography-driven resting-state functional connectivity, which reduces the bias introduced by seed size, shape and position. Next, we demonstrate that structural and functional reconstruction parameters explain a significant portion of intra-and inter-subject variability. Finally, we demonstrate how our proposed approach can be used in a neurosurgical planning context. We believe this approach will promote the exploration of structure-function relationships in a subject-specific aspect and will open new opportunities for connectomics.
    Frontiers in Neuroscience 08/2015; 9(275). DOI:10.3389/fnins.2015.00275 · 3.66 Impact Factor
  • Source
    • "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). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Increasing evidence from cross-sectional and longitudinal molecular-genetic studies suggests that effects of common genetic variations on cognitive functioning increase with aging. We review the influence of candidate genes on brain functioning in old age, focusing on four genetic variations that have been extensively investigated: APOE, BDNF, COMT, and KIBRA. Similar to the behavioral evidence, there are reports from age-comparative studies documenting stronger genetic effects on measures of brain functioning in older adults compared to younger adults. This pattern suggests disproportionate impairments of neural processing among older individuals carrying disadvantageous genotypes. We discuss various factors, including gene-gene interactions, study population characteristics, lifestyle factors, and diseases, that need to be considered in future studies and may help understand inconsistent findings in the extant literature.
    Neuropsychology Review 02/2015; 25(1). DOI:10.1007/s11065-015-9279-8 · 4.59 Impact Factor
Show more