Abstract
The CA3 and dentate gyrus (DG) regions of the hippocampus are considered key for disambiguating sensory inputs from similar experiences in memory, a process termed pattern separation. The neural mechanisms underlying pattern separation, however, have been difficult to compare across species: rodents offer robust recording methods with less human-centric tasks while humans provide complex behavior with less recording potential. To overcome these limitations, we trained monkeys to perform a visual pattern separation task similar to those used in humans while recording activity from single CA3/DG neurons. Using a novel looking pattern assay to evaluate behavior, we find that when animals distinguish recently seen novel images from similar images, indicative of pattern separation, CA3/DG neurons treat the similar images more like novel than repeat images. Further, while many hippocampal neurons respond during pattern separation, only a limited proportion respond to any given pattern separation event, consistent with a sparse distributed code.