Episodic Memory Retrieval, Parietal Cortex, and the Default Mode Network: Functional and Topographic Analyses

Abstract

The default mode network (DMN) is often considered a functionally homogeneous system that is broadly associated with internally directed cognition (e.g. episodic memory, theory of mind, self-evaluation). However, few studies have examined how this network interacts with other networks during putative “default” processes such as episodic memory retrieval. Using fMRI, we investigated the topography and response profile of human parietal regions inside and outside the DMN, independently defined using task-evoked deactivations and resting state functional connectivity, during episodic memory retrieval. Memory retrieval activated posterior nodes of the DMN, particularly the angular gyrus, but also more anterior and dorsal parietal regions that were anatomically separate from the DMN. The two sets of parietal regions showed different resting-state functional connectivity and response profiles. During memory retrieval, responses in DMN regions peaked sooner than non-DMN regions, which in turn showed responses that were sustained until a final memory judgment was reached. Moreover, a parahippocampal region that showed strong resting-state connectivity with parietal DMN regions also exhibited a pattern of task-evoked activity similar to that exhibited by DMN regions. These results suggest that DMN parietal regions directly supported memory retrieval, whereas non-DMN parietal regions were more involved in post-retrieval processes such as memory-based decision making. Finally, a robust functional dissociation within the DMN was observed. While angular gyrus and posterior cingulate/precuneus were significantly activated during memory retrieval, an anterior DMN node in medial prefrontal cortex was strongly deactivated. This latter finding demonstrates functional heterogeneity rather than homogeneity within the DMN during episodic memory retrieval.

EEG microstates as a tool for studying the temporal dynamics of whole-brain neuronal networks: A review

“…network, and fMRI studies of episodic memory retrieval have reported robust functional dissociation within the default mode network: Posterior regions (angular gyrus, posterior cingulate/precuneus) were active during memory retrieval, whereas anterior regions (prefrontal cortex) were inactive (Sestieri et al, 2011). Additional fMRI studies provided further evidence in support of these findings regarding the default mode network (Damoiseaux et al, 2008;Lei et al, 2014).…”

Zazen meditation and no-task resting EEG compared with LORETA intracortical source localization

“…The angular gyrus is an important hub of the posterior part of the DMN which has been shown to be active during memory-based decision making (Sestieri et al 2011) and semantic processing (Seghier et al 2010). In a lexical decision task (discriminating words from nonwords) including the instruction to refocus on breathing after each decision, Zen meditators showed a shortened post-stimulus tail and decreased post-stimulus left angular gyrus BOLD activity compared to controls (Pagnoni et al 2008).…”

Functional Heterogeneity in Posterior Parietal Cortex Across Attention and Episodic Memory Retrieval

“…The attentional account of PPC retrieval effects, while conceptually attractive at a number of levels, has been challenged by recent meta-analytic (Hutchinson et al 2009) and withinstudy (Sestieri et al 2010(Sestieri et al , 2011 evidence that suggests that the PPC subregions associated with top-down and bottom-up attention are anatomically separable from those associated with episodic retrieval (see also Shannon and Buckner (2004) for evidence of further visuospatial attention/retrieval dissociations). For example, drawing on the published attention and memory literatures, Hutchinson et al (2009) systematically assessed the overlap in PPC between effects of top-down and bottom-up attention and those of item memory strength and recollection.…”

“…Interpretation of PPC functional specialization during episodic retrieval also requires consideration of the growing literature demonstrating that PPC contains a mosaic of subregions, each with unique connectivity, functional properties, and receptor composition (Zilles and Palomero-Gallagher 2001;Grefkes and Fink 2005;Silver and Kastner 2009;Uddin et al 2010;Uncapher et al 2010;Nelson et al 2010;Mars et al 2011;Sestieri et al 2011;Yeo et al 2011;Caspers et al 2012). In light of the debate regarding PPC contributions to attention and memory, a particularly relevant aspect of this recent research has been the discovery and characterization of topographically organized maps of attended visual space in IPS and SPL (for review, see Silver and Kastner 2009).…”

“…Although topographic areas in IPS and SPL have been associated broadly with the deployment of top-down spatial attention (Silver and Kastner 2009), there is also meaningful heterogeneity among them Kastner 2008a, 2008b;Sheremata et al 2010), and it is unknown how these regions are engaged, either uniformly or differentially, during complex cognitive acts such as episodic retrieval. Indeed, while initial efforts to parcellate PPC with respect to episodic retrieval have indicated anatomical separation between parietal regions involved in top-down attention and memory (Sestieri et al 2010(Sestieri et al , 2011; see also Nelson et al 2010), no study to date has examined the anatomical and functional correspondences between PPC regions involved in retrieval and topographic parietal visual field maps. Thus, the relationships between parietal regions thought to index item memory strength (familiarity) and recollection and the multiple topographic maps of attended space remain unclear.…”