title: Mechanisms underlying encoding of short-lived versus durable episodic memories.
abstract: We continuously encounter and process novel events in the surrounding world, but only some episodes will leave detailed memory traces that can be recollected after weeks and months. Here, our aim was to monitor brain activity during encoding of events that eventually transforms into long-term stable memories. Previous functional magnetic resonance imaging (fMRI) studies have shown that the degree of activation of different brain regions during encoding is predictive of later recollection success. However, most of these studies tested participants' memories the same day as encoding occurred, whereas several lines of research suggest that extended post-encoding processing is of crucial importance for long-term consolidation. Using fMRI, we tested whether the same encoding mechanisms are predictive of recollection success after hours as after a retention interval of several weeks. Seventy-eight participants were scanned during an associative encoding task and given a source memory test the same day or after ∼6 weeks. We found a strong link between regional activity levels during encoding and recollection success over short time intervals. However, results further showed that durable source memories, i.e., events recollected after several weeks, were not simply the events associated with the highest activity levels at encoding. Rather, strong levels of connectivity between the right hippocampus and perceptual areas, as well as with parts of the self-referential default-mode network, seemed instrumental in establishing durable source memories. Thus, we argue that an initial intensity-based encoding is necessary for short-term encoding of events, whereas additional processes involving hippocampal-cortical communication aid transformation into stable long-term memories.
authors.affiliation: Research Group for Lifespan Changes in Brain and Cognition, Department of Psychology, University of Oslo, 0373 Oslo, Norway, m.h.sneve@psykologi.uio.no.
authors.forename: Markus H
authors.identifier: http://orcid.org/0000-0001-7644-7915
authors.initials: MH
authors.lastname: Sneve
authors.affiliation: Research Group for Lifespan Changes in Brain and Cognition, Department of Psychology, University of Oslo, 0373 Oslo, Norway.
authors.forename: Håkon
authors.initials: H
authors.lastname: Grydeland
authors.affiliation: Umeå Center for Functional Brain Imaging, Umeå University, S-90187, Umeå, Sweden, and.
authors.forename: Lars
authors.initials: L
authors.lastname: Nyberg
authors.affiliation: Helen Wills Neuroscience Institute and Department of Psychology, University of California, Berkeley, Berkeley, California 94720.
authors.forename: Ben
authors.initials: B
authors.lastname: Bowles
authors.affiliation: Research Group for Lifespan Changes in Brain and Cognition, Department of Psychology, University of Oslo, 0373 Oslo, Norway.
authors.forename: Inge K
authors.initials: IK
authors.lastname: Amlien
authors.affiliation: Research Group for Lifespan Changes in Brain and Cognition, Department of Psychology, University of Oslo, 0373 Oslo, Norway.
authors.forename: Espen
authors.initials: E
authors.lastname: Langnes
authors.affiliation: Research Group for Lifespan Changes in Brain and Cognition, Department of Psychology, University of Oslo, 0373 Oslo, Norway, Department of Physical Medicine and Rehabilitation, Unit of Neuropsychology, Oslo University Hospital, 0424 Oslo, Norway.
authors.forename: Kristine B
authors.initials: KB
authors.lastname: Walhovd
authors.affiliation: Research Group for Lifespan Changes in Brain and Cognition, Department of Psychology, University of Oslo, 0373 Oslo, Norway, Department of Physical Medicine and Rehabilitation, Unit of Neuropsychology, Oslo University Hospital, 0424 Oslo, Norway.
authors.forename: Anders M
authors.initials: AM
authors.lastname: Fjell
mesh_terms: D000328:Adult; D001245:Association Learning / Q000502:physiology; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology*; D005260:Female; D006624:Hippocampus / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D061212:Memory, Episodic; D011939:Mental Recall / Q000502:physiology*; D012153:Retention, Psychology / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: FMRI; consolidation; hippocampus; long-term memory; subsequent memory
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