Abstract
Episodic memory capacity requires several processes, including mnemonic discrimination of similar experiences, termed pattern separation, and holistic retrieval of multidimensional experiences given a cue, termed pattern completion. Both computations seem to rely on the hippocampus proper, but they also seem to be instantiated by distinct hippocampal subfields. Thus, we investigated whether individual differences in behavioral expressions of pattern separation and pattern completion were correlated after accounting for general mnemonic ability. Young adult participants learned events comprised of a scene-animal-object triad. In the pattern separation task, we estimated mnemonic discrimination using lure classification for events that contained a similar lure element. In the pattern completion task, we estimated holistic recollection using dependency in retrieval success for different associations from the same event. Although overall accuracies for the two tasks correlated as expected, specific measures of individual variation in holistic retrieval and mnemonic discrimination did not correlate, suggesting that these two processes involve distinguishable properties of episodic memory.
Highlights
Episodic memory binds together the diverse co-occurring elements that make up the specific events of our lives, forming distinctive and complex events that can guide ongoing behavior
Remembering a past event with high specificity is optimized by pattern separation processes, whereby similar experiences are assigned to non-overlapping neural codes in the service of preserving each event’s distinctiveness
Pattern completion processes enables this network of relations to be retrieved holistically, such that one constituent of an event can elicit the retrieval of other elements from the same event
Summary
Episodic memory binds together the diverse co-occurring elements that make up the specific events of our lives, forming distinctive and complex events that can guide ongoing behavior. This reinstatement signal is more robust within the CA3 compared to the dentate gyrus (Grande et al, 2019) Together, these findings support the idea that the retrieval of multiple elements of an event given the same cue is mutually contingent, and that this computation may, in part, rely on hippocampal pattern completion. We tested whether general episodic memory performance that is nonspecific to pattern separation and completion would correlate between the two tasks If this relation between gross accuracy of the two tasks exists, but the correlation between holistic retrieval and lure classification is not detected, this result would substantiate the idea that individual differences on pattern separation and pattern completion are unrelated. It is important to note, for naming heuristic purposes, pattern separation and pattern completion tasks here refer to the dependent variables of interest from each task, without the assumption that these processes are the only one at play in each task
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