Hippocampal Memory Traces Are Differentially Modulated by Experience, Time, and Adult Neurogenesis

By C. Denny, M. Kheirbek, Eva L. Alba, Kenji F. Tanaka, R. A. Brachman, Kimberly B. Laughman, Nicole K. Tomm, G. Turi, Attila Losonczy, R. Hen. 2014

515 citations recorded by the source corpus.

SUMMARY Memory traces are believed to be ensembles of cells used to store memories. To visualize memory traces, we created a transgenic line that allows for the comparison between cells activated during encoding and expression of a memory. Mice re-exposed to a fear-inducing context froze more and had a greater percentage of reactivated cells in the dentate gyrus (DG) and CA3 than mice exposed to a novel context. Over time, these differences disappeared, in keeping with the observation that memories become generalized. Optogenetically silencing DG or CA3 cells that were recruited during encoding of a fear-inducing context prevented expression of the corresponding memory. Mice with reduced neurogenesis displayed less contextual memory and less reactivation in CA3 but, surprisingly, normal reactivation in the DG. These studies suggest that distinct memory traces are located in the DG and in CA3 but that the strength of the memory is related to reactivation in CA3.

Subfields: Cellular and Molecular Neuroscience, Cognitive Neuroscience, Developmental Neuroscience

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Citations in the corpus

The Persistence and Transience of Memory. (2017, methodology): “Using these methods, reactivation rates were quite modest in some regions (e.g., dentate gyrus, (cid:1) 5%; Denny et al., 2014) but more robust in others (e.g., CA1, (cid:1) 40%; Tanaka et al., 2014).”
Adult Neurogenesis in the Hippocampus: From Stem Cells to Behavior. (2016, unknown): “…of DG neurons upon re-exposure to the conditioned context, whereas CA1 neurons preferentially reactivated during the same recall test (Deng et al., 2013); on the other hand, optogenetically silencing DG or CA3 cells activated during memory encoding prevented memory recall (Denny et al., 2014).”
Mapping of brain activity by automated volume analysis of immediate early genes (2016, unknown): “Up-regulation of their expression usually lags neuronal stimulation by about 30 minutes, and their expression can outlast the end of activity by over 4 hours (Barnes et al., 2015), so that IEGs can be considered to encode a short-term memory trace of the activity (Denny et al., 2014).”
Memory engrams: Recalling the past and imagining the future (2020, background): “However, the extent to which DG neurons that were activated 25 days after contextual fear conditioning overlapwith DG neurons active during training remains an open question (40, 51).”
Loss of Ensemble Segregation in Dentate Gyrus, but not in Somatosensory Cortex, during Contextual Fear Memory Generalization (2016, background): “These results suggest that the contextual fear memories in our experimental condition were initially specific to the context, but became less specific within 9 days.”