title: The episodic engram transformed: Time reduces retrieval-related brain activity but correlates it with memory accuracy.
abstract: We took snapshots of human brain activity with fMRI during retrieval of realistic episodic memory over several months. Three groups of participants were scanned during a memory test either hours, weeks, or months after viewing a documentary movie. High recognition accuracy after hours decreased after weeks and remained at similar levels after months. In contrast, BOLD activity in a retrieval-related set of brain areas during correctly remembered events was similar after hours and weeks but significantly declined after months. Despite this reduction, BOLD activity in retrieval-related regions was positively correlated with recognition accuracy only after months. Hippocampal engagement during retrieval remained similar over time during recall but decreased in recognition. Our results are in line with the hypothesis that hippocampus subserves retrieval of real-life episodic memory long after encoding, its engagement being dependent on retrieval demands. Furthermore, our findings suggest that over time episodic engrams are transformed into a parsimonious form capable of supporting accurate retrieval of the crux of events, arguably a critical goal of memory, with only minimal network activation.
authors.affiliation: Department of Neurobiology, The Weizmann Institute of Science, Rehovot, Israel. orit.furman@weizmann.ac.il
authors.forename: Orit
authors.initials: O
authors.lastname: Furman
authors.forename: Avi
authors.initials: A
authors.lastname: Mendelsohn
authors.forename: Yadin
authors.initials: Y
authors.lastname: Dudai
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000098:blood supply / Q000502:physiology*; D001931:Brain Mapping; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation; D011930:Reaction Time; D021641:Recognition, Psychology / Q000502:physiology*; D013223:Statistics as Topic; D011795:Surveys and Questionnaires; D013997:Time Factors; D014163:Transfer, Psychology; D055815:Young Adult
chemical_list: D010100:Oxygen