Neural mechanisms supporting the extraction of general knowledge across episodic memories

Abstract

a b s t r a c t a r t i c l e i n f oGeneral knowledge acquisition entails the extraction of statistical regularities from the environment. At high levels of complexity, this may involve the extraction, and consolidation, of associative regularities across event memories. The underlying neural mechanisms would likely involve a hippocampo-neocortical dialog, as proposed previously for system-level consolidation. To test these hypotheses, we assessed possible differences in consolidation between associative memories containing cross-episodic regularities and unique associative memories. Subjects learned face-location associations, half of which responded to complex regularities regarding the combination of facial features and locations, whereas the other half did not. Importantly, regularities could only be extracted over hippocampus-encoded, associative aspects of the items. Memory was assessed both immediately after encoding and 48 h later, under fMRI acquisition. Our results suggest that processes related to system-level reorganization occur preferentially for regular associations across episodes. Moreover, the buildup of general knowledge regarding regular associations appears to involve the coordinated activity of the hippocampus and mediofrontal regions. The putative cross-talk between these two regions might support a mechanism for regularity extraction. These findings suggest that the consolidation of cross-episodic regularities may be a key mechanism underlying general knowledge acquisition.

Young adults self-derive and retain new factual knowledge through memory integration

“…This finding is consistent with Sweegers and colleagues (2014), the only analogous investigation of long-term retention of integrated knowledge conducted with adults to date. They found that directly learned, cross-episode relations were preferentially consolidated in memory as compared to isolated memories.…”

“…In contrast, even when individuals become aware of the prototypical AB:BC paired associate structure, the arbitrary nature of the relations likely precludes deeper processing that could further enhance integration performance. Consistent with this interpretation, explicit awareness is also associated with integration in pattern-learning tasks in which individuals must extract subtle rules, such as how the spatial and non-spatial orientation of various fractals determine weather outcomes (Kumaran et al, 2009) or rules regarding face attributes repeatedly encountered at specific locations (Sweegers et al, 2014). Thus, it is possible that the nature of the stimuli might account for greater variability in explicit awareness of the relational structure relative to research utilizing more contrived, arbitrary items.…”

“…Critically, the formation of an integrated knowledge base also permits flexible extension beyond direct experience, enabling self-derivation of new thoughts, ideas, and understandings. Prior research on productive knowledge extension provides important insight into the mechanisms involved in memory integration in nonhuman animals (e.g., Bunsey & Eichenbaum, 1996; Dusek & Eichenbaum, 1997; Tse et al, 2007; 2011), in adults (e.g., Bauer & Jackson, 2015; Kumaran, Summerfield, Hassabis, & Maguire, 2009; Preston, Shrager, Dudukovic, & Gabrieli, 2004; Schlichting, Zeithamova, & Preston, 2014; Shohamy & Wagner, 2008; Sweegers, Takashima, Fernández, & Talamini, 2014; Zeithamova, Dominick, & Preston, 2012a; Zeithamova & Preston, 2010), and in children (e.g., Bauer, King, Larkina, Varga, & White, 2012; Bauer, Varga, King, Nolen, & White, 2015). Yet although productive extension is presumed to serve as a key mechanism through which a knowledge base is formed (Bauer, 2012; Bauer & Varga, 2016; Preston & Eichenbaum, 2013; Siegler, 1989), the self-derivation and later retention of factual knowledge newly derived through integration has not been examined in adults.…”

“…Conversely, in another incidental learning task using arbitrary paired associates, all individuals exhibited explicit knowledge of the relations (Schlichting & Preston, 2014). Furthermore, when individuals are directly instructed to attend to the relational structure in rule-governed tasks, such as predicting the weather based on the spatial structure of fractals (e.g., Kumaran et al, 2009) or determining the patterns governing face-location pairings (e.g., Sweegers et al, 2014), there is variability in the extent to which they express and deploy their explicit knowledge of the task structure, which is positively associated with integration. To extend beyond these studies which have exclusively relied on arbitrary materials, in Experiment 2, we assessed whether explicit awareness of the opportunity to integrate was associated with the capacity to self-derive new factual knowledge through integration.…”

Hippocampal–medial prefrontal circuit supports memory updating during learning and post-encoding rest

“…Because previous studies on similar topics (Kumaran et al, 2009; van Kesteren et al, 2010b, 2014; Sweegers et al, 2013) have identified a range of activation foci throughout the medial surface of PFC, we combined medial orbitofrontal and rostroanterior cingulate to create an MPFC ROI for each participant. ROIs were then aligned to each individual’s functional data using transformations applied in FLIRT, as described above.…”