Abstract
Episodic memories reflect a bound representation of multimodal features that can be reinstated with varying precision. Yet little is known about how brain networks involved in memory, including the hippocampus and posterior-medial (PM) and anterior-temporal (AT) systems, interact to support the quality and content of recollection. Participants learned color, spatial, and emotion associations of objects, later reconstructing the visual features using a continuous color spectrum and 360-degree panorama scenes. Behaviorally, dependencies in memory were observed for the gist but not precision of event associations. Supporting this integration, hippocampus, AT, and PM regions showed increased connectivity and reduced modularity during retrieval compared to encoding. These inter-network connections tracked a multidimensional, objective measure of memory quality. Moreover, distinct patterns of connectivity tracked item color and spatial memory precision. These findings demonstrate how hippocampal-cortical connections reconfigure during episodic retrieval, and how such dynamic interactions might flexibly support the multidimensional quality of remembered events.
Highlights
Memories for past events are highly complex, allowing us to travel back in time and subjectively reexperience episodes in our lives
Much research has demonstrated widespread increases in functional connectivity during episodic retrieval (Fornito et al, 2012; Geib et al, 2017a; King et al, 2015; Schedlbauer et al, 2014; St Jacques et al, 2011; Westphal et al, 2017), yet how these changes relate to the phenomenology of recollective experience has remained unknown
While several prominent accounts have posited that medial temporal regions, including parahippocampal cortex (PHC) and perirhinal cortex (PRC), provide memories with complementary spatial and item-specific representations, respectively, (Davachi, 2006; Diana et al, 2007; Eichenbaum et al, 2012; Graham et al, 2010), a recent model - the PMAT framework - extends this representational sensitivity to large scale cortical networks (Ranganath and Ritchey, 2012; Ritchey et al, 2015a)
Summary
Memories for past events are highly complex, allowing us to travel back in time and subjectively reexperience episodes in our lives. Episodic reconstruction is thought to be facilitated by hippocampal-neocortical processes that rebuild the rich content and quality of past events within a spatio-temporal framework (Barry and Maguire, 2019; Ranganath, 2010; Ritchey et al, 2015a; Robin, 2018) and integrate them with prior knowledge (Morton et al, 2017). Distinct cortical areas support the different building blocks of episodic memory: for instance, parahippocampal cortex (PHC) is thought to provide the hippocampus with spatial context information, whereas perirhinal cortex (PRC) codes for items within this context (Davachi, 2006; Diana et al, 2007; Diana et al, 2010; Staresina et al, 2013; Staresina et al, 2011) These medial temporal cortical regions are situated within two large-scale networks (Ranganath and Ritchey, 2012; Ritchey et al, 2015a). In line with the representational organization of the PMAT framework, we predicted that functional connectivity of PM and AT systems would track memory precision for spatial context and item information, respectively
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