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Nature. 2016 Jun 2;534(7605):115-8. doi: 10.1038/nature17955. Epub 2016 May 23.

A shared neural ensemble links distinct contextual memories encoded close in time.

Author information

1
Departments of Neurobiology, Psychiatry &Biobehavioral Sciences and Psychology, Integrative Center for Learning and Memory, Brain Research Institute, University of California, Los Angeles, California 90095, USA.
2
Departments of Neurology and Psychiatry &Biobehavioral Sciences, Integrative Center for Learning and Memory, Brain Research Institute, University of California, Los Angeles, California 90095, USA.
3
West Los Angeles VA Medical Center, 11301 Wilshire Blvd, Los Angeles, California 90073, USA.
4
Department of Neurosciences, University of California, San Diego, La Jolla, California 92093, USA.
5
Veterans Affairs Medical Center, San Diego, California 92161, USA.
6
Departments of Cell Biology and Neurosciences, Institute for Childhood and Neglected Diseases, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
7
Division of Hematology/Oncology, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA.

Abstract

Recent studies suggest that a shared neural ensemble may link distinct memories encoded close in time. According to the memory allocation hypothesis, learning triggers a temporary increase in neuronal excitability that biases the representation of a subsequent memory to the neuronal ensemble encoding the first memory, such that recall of one memory increases the likelihood of recalling the other memory. Here we show in mice that the overlap between the hippocampal CA1 ensembles activated by two distinct contexts acquired within a day is higher than when they are separated by a week. Several findings indicate that this overlap of neuronal ensembles links two contextual memories. First, fear paired with one context is transferred to a neutral context when the two contexts are acquired within a day but not across a week. Second, the first memory strengthens the second memory within a day but not across a week. Older mice, known to have lower CA1 excitability, do not show the overlap between ensembles, the transfer of fear between contexts, or the strengthening of the second memory. Finally, in aged mice, increasing cellular excitability and activating a common ensemble of CA1 neurons during two distinct context exposures rescued the deficit in linking memories. Taken together, these findings demonstrate that contextual memories encoded close in time are linked by directing storage into overlapping ensembles. Alteration of these processes by ageing could affect the temporal structure of memories, thus impairing efficient recall of related information.

Comment in

PMID:
27251287
PMCID:
PMC5063500
DOI:
10.1038/nature17955
[Indexed for MEDLINE]
Free PMC Article

Conflict of interest statement

The authors declare no competing financial interests.

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