The Hippocampus Remains Activated over the Long Term for the Retrieval of Truly Episodic Memories
Open Access
- 24 August 2012
- journal article
- research article
- Published by Public Library of Science (PLoS) in PLOS ONE
- Vol. 7 (8), e43495
- https://doi.org/10.1371/journal.pone.0043495
Abstract
The role of the hippocampus in declarative memory consolidation is a matter of intense debate. We investigated the neural substrates of memory retrieval for recent and remote information using functional magnetic resonance imaging (fMRI). 18 young, healthy participants learned a series of pictures. Then, during two fMRI recognition sessions, 3 days and 3 months later, they had to determine whether they recognized or not each picture using the “Remember/Know” procedure. Presentation of the same learned images at both delays allowed us to track the evolution of memories and distinguish consistently episodic memories from those that were initially episodic and then became familiar or semantic over time and were retrieved without any contextual detail. Hippocampal activation decreased over time for initially episodic, later semantic memories, but remained stable for consistently episodic ones, at least in its posterior part. For both types of memories, neocortical activations were observed at both delays, notably in the ventromedial prefrontal and anterior cingulate cortices. These activations may reflect a gradual reorganization of memory traces within neural networks. Our data indicate maintenance and strengthening of hippocampal and cortico-cortical connections in the consolidation and retrieval of episodic memories over time, in line with the Multiple Trace theory (Nadel and Moscovitch, 1997). At variance, memories becoming semantic over time consolidate through strengthening of cortico-cortical connections and progressive disengagement of the hippocampus.This publication has 58 references indexed in Scilit:
- Memory formation and long-term retention in humans and animals: Convergence towards a transformation account of hippocampal–neocortical interactionsNeuropsychologia, 2010
- A Simple Way to Improve Anatomical Mapping of Functional Brain ImagingJournal of Neuroimaging, 2010
- Event-related fMRI studies of episodic encoding and retrieval: Meta-analyses using activation likelihood estimationNeuropsychologia, 2009
- The parietal cortex and episodic memory: an attentional accountNature Reviews Neuroscience, 2008
- Top-down and bottom-up attention to memory: A hypothesis (AtoM) on the role of the posterior parietal cortex in memory retrievalNeuropsychologia, 2008
- MNESIS: Towards the Integration of Current Multisystem Models of MemoryNeuropsychology Review, 2008
- Sleep transforms the cerebral trace of declarative memoriesProceedings of the National Academy of Sciences of the United States of America, 2007
- Sleep-Related Hippocampo-Cortical Interplay during Emotional Memory RecollectionPLoS Biology, 2007
- The Medial Temporal Lobe and Recognition MemoryAnnual Review of Neuroscience, 2007
- Hippocampal Activation for Autobiographical Memories over the Entire Lifetime in Healthy Aged Subjects: An fMRI StudyCerebral Cortex, 2007