Memory Traces Reflect How They Were Last Retrieved

Abstract

Episodic memories are known to change with each act of retrieval. We hypothesize that accessing semantic knowledge in different ways during episodic retrieval--from unique perceptual features to taxonomic and thematic context--shapes how those memories are subsequently represented during recognition. In this functional magnetic resonance imaging (fMRI) study, human participants learned novel word-image pairs and underwent re-exposure that required accessing semantic knowledge at one of three different levels: item, category, or theme. Participants then completed a recognition task. Although behavioral memory performance was matched across conditions, neural activity during recognition varied based on prior semantic access history. Recognition patterns could be classified according to prior semantic access in early visual cortex, ventral temporal cortex and the hippocampus for remembered concepts. A whole-brain searchlight analysis revealed bilateral clusters along the ventral visual stream where semantic access history was decodable. To further characterize how prior semantic access history shaped neural representations during recognition, we tested whether memories accessed at the same semantic level were expressed more similarly or distinctly in the brain. Category-level access increased similarity among items in early visual cortex, while item-level access led to more differentiated representations in the visual word form area. Together, these findings show that how we access semantic knowledge during episodic retrieval leaves measurable traces in subsequent neural representations, revealing how semantic-episodic interactions shape memory representations.