RESOLVING MEMORY CLUTTER BASED ON COMPETITION: BEHAVIORAL, AND NEUROIMAGING INVESTIGATIONS

Abstract

We quickly memorize relationships between items and contexts within episodic experiences. While this ability of relational memory enables us to use past experiences to guide our future behaviors, it can also bring about competitions between overlapping memories. How does the brain resolve the potential memory clutter? Previous studies have demonstrated that the brain reduces the competition by forming separated memory representations across overlapping experiences, and that the memory clutter can be attenuated based on effortful inhibition of distracting information. Much of this dissertation work provides evidence of a novel neural mechanism whereby the brain minimizes the competition by re-organizing overlapping memory representations based on context-based prediction signal. First, we demonstrated that moderate levels of incorrect prediction of an item within a familiar context weaken memory of the mispredicted item. This finding suggests that, through this process, the brain determines which memory is an irrelevant aspect of the environment, and prunes it from long-term memory storage. Second, we investigated how the previously weakened memory regains its memory strength when re-experienced later. We found that the weakened item representation becomes incrementally differentiated from its initial context after subsequent restudy, and we also observed that the neural differentiation effect is mediated by the amount of incorrect prediction. This set of findings sheds light on how the brain reorganizes existing overlapping memories based on prediction signal to minimize potential memory clutter. Finally, we investigated a novel online mechanism whereby the brain prevents interference between repeated experiences during encoding a later one. We observed that the degree of representational overlap across repeated experiences regulates subsequent source memory. If an initial representation of an item is less reinstated when it is re-experienced later, the initial representation suffers less from competition from the novel context of the later encounter compared to when it was highly reinstated. To summarize, this work characterizes the novel neural mechanisms wherein the brain minimizes memory competition by regulating representations of overlapping experiences.