The role of the hippocampus in resolving memory interference has been greatly elucidated by considering the relationship between the similarity of visual stimuli (input) and corresponding similarity of hippocampal activity patterns (output). However, these input-output functions can take surprisingly different forms. Here, we reconcile seemingly conflicting findings by considering the possibility that the hippocampus prioritizes different dimensions of visual similarity across different stages of learning.
First, we generated a set of natural scene images from two visual categories and rigorously characterized visual similarity using a wide array of methods: neural networks, artificial intelligence models, and human perceptual and memory decisions. We then identified two orthogonal dimensions of visual similarity that each predicted memory interference, but that did so at distinct stages of learning. Using high-resolution fMRI, we then tested for dimension-specific input-output functions within the hippocampus.
Within CA3 and dentate gyrus (CA3/DG), we show that dimensions of visual similarity were inverted (repulsion) at stages of learning when they contributed to memory interference. In contrast, CA3/DG preserved similarity when dimensions did not contribute to interference. These findings reveal that hippocampal representations of visually-similar stimuli are highly dynamic and critically depend on the dimensions of similarity that currently contribute to memory interference.
This work was supported by National Institutes of Health grant NIH-NINDS 2R01NS089729 to B.A.K., Ruth L. Kirschstein NRSA Individual Predoctoral Fellowship (from the National Institutes of Health) grant F31NS126016 to W.G., and NIH-NIA 1R01AG092600 to U.M. B.A.K. discloses support for the research of this work from the National Institutes of Health (NIH-NINDS grant 2R01NS089729).
W.G. discloses support for the research of this work from the National Institutes of Health (NIH-NINDS Ruth L. Kirschstein NRSA Individual Predoctoral Fellowship grant F31NS126016). U.M. discloses support for the research of this work from the National Institutes of Health (NIH-NIA 1R01AG092600).
S.M. declares no relevant funding. These authors contributed equally: Guo Wanjia, Dominik Grätz. Department of Psychology, University of Oregon, Eugene, OR, USA Soroush Mirjalili, Guo Wanjia, Dominik Grätz, Eric Z.
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