Competitive remembering: Neural systems for overcoming interference in episodic memory

One of the most fundamental challenges to understanding episodic memories is to understand how we form, store, and retrieve countless memories of overlapping or related events. From the perspective of neural processing and organization, it is a daunting challenge to represent and maintain memories in an efficient mariner The present work is focused on the influence of interference at three stages of mnemonic processing. Broadly, these themes cover: (1) mechanisms engaged at encoding that help minimize forgetting of previously encoded, overlapping events; (2) mechanisms engaged during selective retrieval that relate to dynamic changes in the strength of target vs. competing memories; and (3) mechanisms that support reorientation of retrieval goals such that previously irrelevant, weak memories can be retrieved in the face of interference from more dominant memories.;The first theme of this dissertation relates to the mechanisms that operate during encoding to help protect memories from interference-related forgetting. Evidence is presented that the retention of previously encoded memories is related to the engagement of structures within the medial temporal lobes (namely, the hippocampus) during the acquisition of new memories. Moreover, it is argued that this protection against forgetting occurs through reactivation of past events during new encoding. These results are considered with respect to models of hippocampal function and classic interference theory.;The second theme of this dissertation focuses on mechanisms engaged during selective retrieval when a target memory is retrieved amidst interference from related memories. Evidence is presented demonstrating that repeated acts of selective retrieval influence the strength of both those memories that are selected as well as those memories that are selected-against. It is argued that the weakening of selected-against, competing memories is associated with reduced demands on prefrontal cortex during the retrieval of target memories. These findings are considered in terms of an adaptive memory system, wherein interference between memories is detected and resolved by mechanisms in prefrontal cortex, with the gradual weakening of interfering memories lessening the demands on these prefrontal mechanisms.;The final theme considered in this dissertation relates to the mechanisms that allow for the retrieval of memories that were previously selected-against. That is, retrieval demands are particularly high when mnemonic goals change and memories that were previously irrelevant are now goal-relevant. Data are presented highlighting the role of prefrontal cortex in supporting this flexible reorientation of retrieval processes such that weak memory traces can be recovered despite interference from more dominant (previously relevant) memories. Specifically, it is argued that the same prefrontal mechanisms that benefit from the weakening of interfering memories are selectively recruited when these weakened memories must be retrieved. These data are considered with respect to other prefrontal mechanisms that support retrieval amidst competition.;Together, these studies highlight the cognitive and neural mechanisms that allow episodic memory to function in an adaptive manner, elucidating the factors that support competitive encoding, retrieval, and flexible reorientation of retrieval goals.