The default network and processing of personally relevant information: Converging evidence from task-related modulations and functional connectivity

Rotman Research Institute at Baycrest, Toronto, Ontario, Canada.
Neuropsychologia (Impact Factor: 3.3). 11/2010; 48(13):3815-23. DOI: 10.1016/j.neuropsychologia.2010.09.007
Source: PubMed


Despite a growing interest in the default network (DN), its composition and function are not fully known. Here we examined whether the DN, as a whole, is specifically active during a task involving judgments about the self, or whether this engagement extends to judgments about a close other. We also aimed to provide converging evidence of DN involvement from across-task functional connectivity, and resting-state functional connectivity analyses, to provide a more comprehensive delineation of this network. Using functional MRI we measured brain activity in young adults during tasks and rest, and utilized a multivariate method to assess task-related changes as well as functional connectivity. An overlapping set of regions showed increased activity for judgments about the self, and about a close other, and strong functional connectivity with the posterior cingulate, a critical node of the DN. These areas included ventromedial prefrontal cortex, posterior parietal cortex, and medial temporal regions, all thought to be part of the DN. Several additional regions, such as the left inferior frontal gyrus and bilateral caudate, also showed the same pattern of activity and connectivity. These results provide evidence that the default network, as an integrated whole, supports internally oriented cognition involving information that is personally relevant, but not limited specifically to the self. They also suggest that the DN may be somewhat more extensive than currently thought.

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    • "This result may also fit with previous accounts suggesting that the functional specialization of the medial prefrontal-parietal subsystem is related to self-referential or personally-relevant thought, whereas the medial temporal network is closely related to memory retrieval, imagery retrieval or scene construction (Andrews-Hanna et al., 2010; Andrews-Hanna et al., 2014; Grigg & Grady, 2010a; Kim, 2012). Based on these theories of the functional specialization of the subnetworks , it would follow that only the episodic task would require coordinated activity across the two networks in question. "
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    ABSTRACT: Several recent studies have compared episodic and spatial memory in neuroimaging paradigms in order to understand better the contribution of the hippocampus to each of these tasks. In the present study, we build on previous findings showing common neural activation in default network areas during episodic and spatial memory tasks based on familiar, real-world environments (Hirshhorn et al., Neuropsychologia 2012; 50(13): 3094-3106). Following previous demonstrations of the presence of functionally connected sub-networks within the default network, we performed seed-based functional connectivity analyses to determine how, depending on the task, the hippocampus and prefrontal cortex differentially couple with one another and with distinct whole-brain networks. We found evidence for a medial prefrontal-parietal network and a medial temporal lobe network, which were functionally connected to the prefrontal and hippocampal seeds, respectively, regardless of the nature of the memory task. However, these two networks were functionally connected with one another during the episodic memory task, but not during spatial memory tasks. Replicating previous reports of fractionation of the default network into stable sub-networks, this study also shows how these sub-networks may flexibly couple and uncouple with one another based on task demands. These findings support the hypothesis that episodic memory and spatial memory share a common medial temporal lobe-based neural substrate, with episodic memory recruiting additional prefrontal sub-networks. © 2014 Wiley Periodicals, Inc.
    Full-text · Article · Jan 2015 · Hippocampus
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    • "To examine the three networks we used regions identified as major nodes in these networks. For the DMN we used a PCC region (X, Y and Z MNI coordinates: À 4, À 48, 28) using coordinates from previously published data (Grady et al., 2012; Grigg and Grady, 2010a,2010b), and which are very similar to coordinates published by other groups (e.g., Buckner et al., 2009; Leech et al., 2011; Toro et al., 2008). For the SLN and FPC we used a single region, the aIFO, because this area is strongly coupled to both networks (Allen et al., 2011; Seeley et al., 2007; Vincent et al., 2008). "
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    ABSTRACT: Bilingual older adults typically have better performance on tasks of executive control (EC) than do their monolingual peers, but differences in brain activity due to language experience are not well understood. Based on studies showing a relation between the dynamic range of brain network activity and performance on EC tasks, we hypothesized that life-long bilingual older adults would show increased functional connectivity relative to monolinguals in networks related to EC. We assessed intrinsic functional connectivity and modulation of activity in task vs. fixation periods in two brain networks that are active when EC is engaged, the frontoparietal control network (FPC) and the salience network (SLN). We also examined the default mode network (DMN), which influences behavior through reduced activity during tasks. We found stronger intrinsic functional connectivity in the FPC and DMN in bilinguals than in monolinguals. Although there were no group differences in the modulation of activity across tasks and fixation, bilinguals showed stronger correlations than monolinguals between intrinsic connectivity in the FPC and task-related increases of activity in prefrontal and parietal regions. This bilingual difference in network connectivity suggests that language experience begun in childhood and continued throughout adulthood influences brain networks in ways that may provide benefits in later life.
    Full-text · Article · Nov 2014 · Neuropsychologia
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    • "In preparation for these analyses, we first averaged each consecutive 5 volumes from the resting run, to produce 29 “blocks” of 10s each (excluding the first 5 TRs to allow for signal normalization). This averaging process effectively produced a low-pass filter of 0.1Hz and reduced temporal noise (Grigg and Grady, 2010a,b). Then for each time point, we extracted the mean signal from each seed voxel and then correlated the signal from both seeds (i.e., the MTL and dmPFC for the first analysis and the vPCC and dPCC for the second analysis) to all other voxels in the brain, across participants. "
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    ABSTRACT: Recent work suggests that the default mode network (DMN) includes two core regions, the ventromedial prefrontal cortex and posterior cingulate cortex (PCC), and several unique subsystems that are functionally distinct. These include a medial temporal lobe (MTL) subsystem, active during remembering and future projection, and a dorsomedial prefrontal cortex (dmPFC) subsystem, active during self-reference. The PCC has been further subdivided into ventral (vPCC) and dorsal (dPCC) regions that are more strongly connected with the DMN and cognitive control networks, respectively. The goal of this study was to examine age differences in resting state functional connectivity within these subsystems. After applying a rigorous procedure to reduce the effects of head motion, we used a multivariate technique to identify both common and unique patterns of functional connectivity in the MTL vs. the dmPFC, and in vPCC vs. dPCC. All four areas had robust functional connectivity with other DMN regions, and each also showed distinct connectivity patterns in both age groups. Young and older adults had equivalent functional connectivity in the MTL subsystem. Older adults showed weaker connectivity in the vPCC and dmPFC subsystems, particularly with other DMN areas, but stronger connectivity than younger adults in the dPCC subsystem, which included areas involved in cognitive control. Our data provide evidence for distinct subsystems involving DMN nodes, which are maintained with age. Nevertheless, there are age differences in the strength of functional connectivity within these subsystems, supporting prior evidence that DMN connectivity is particularly vulnerable to age, whereas connectivity involving cognitive control regions is relatively maintained. These results suggest an age difference in the integrated activity among brain networks that can have implications for cognition in older adults.
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