Cortical Overlap and Cortical-Hippocampal Interactions Predict Subsequent True and False Memory.

The declarative memory system allows us to accurately recognize a countless number of items and events, particularly those strengthened by repeated exposure. However, increased familiarity due to repetition can also lead to false recognition of related but new items, particularly when mechanisms supporting fine-grain mnemonic discrimination fail. The hippocampus is thought to be particularly important in separating overlapping cortical inputs during encoding so that similar experiences can be differentiated. In the current study of male and female human subjects, we examine how neural pattern similarity between repeated exemplars of a given concept (e.g., apple) influences true and false memory for target or lure images. Consistent with past work, we found that subsequent true recognition was related to pattern similarity between concept exemplars and the entire encoding set (global encoding similarity), particularly in ventral visual stream. In addition, memory for an individual target exemplar (a specific apple) could be predicted solely by the degree of pattern overlap between the other exemplars (different apple pictures) of that concept (concept-specific encoding similarity). Critically, subsequent false memory for lures was mitigated when high concept-specific similarity in cortical areas was accompanied by differentiated hippocampal representations of the corresponding exemplars. Furthermore, both true and false memory entailed the reinstatement of concept-related information at varying levels of specificity. These results link both true and false memory to a measure of concept strength expressed in the overlap of cortical representations, and importantly, illustrate how the hippocampus serves to separate concurrent cortical overlap in the service of detailed memory.