Decoding the Tradeoff between Encoding and Retrieval to Predict Memory for Overlapping Events

Abstract

Most of our experiences have some overlap with past events and this overlap can function as a cue that triggers memory retrieval. However, retrieval of the past potentially comes at the expense of encoding new memories. For example, upon encountering an acquaintance, you might find yourself remembering a previous conversation with this acquaintance only to realize that you have not encoded the current conversation. This tradeoff between memory encoding and retrieval is of central importance to computational models of episodic memory and is particularly relevant when new events overlap with past events. However, prior studies have not directly linked neural markers of encoding/retrieval tradeoffs to behavioral measures of how overlapping events are remembered. Here, by decoding patterns of scalp electroencephalography (EEG), we show that tradeoffs between encoding and retrieval states are reflected in distributed patterns of neural activity and, critically, that these neural tradeoffs predict how overlapping events will later be remembered. Namely, overlapping events were less likely to be subsequently remembered if neural patterns were biased toward a retrieval state (or, conversely, away from an encoding state). Additionally, we show that neural markers of encoding vs. retrieval states are surprisingly independent from previously-described EEG predictors of subsequent memory. Instead, we show that previously-described EEG predictors of subsequent memory are better explained by task engagement than by memory encoding, per se. Collectively, our findings reveal that neural tradeoffs between encoding and retrieval states determine how overlapping events will subsequently be remembered.