title: A shared neural ensemble links distinct contextual memories encoded close in time.
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.
authors.affiliation: 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.
authors.forename: Denise J
authors.initials: DJ
authors.lastname: Cai
authors.affiliation: 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.|Departments of Neurology and Psychiatry &Biobehavioral Sciences, Integrative Center for Learning and Memory, Brain Research Institute, University of California, Los Angeles, California 90095, USA.|West Los Angeles VA Medical Center, 11301 Wilshire Blvd, Los Angeles, California 90073, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Aharoni
authors.affiliation: Departments of Neurology and Psychiatry &Biobehavioral Sciences, Integrative Center for Learning and Memory, Brain Research Institute, University of California, Los Angeles, California 90095, USA.|West Los Angeles VA Medical Center, 11301 Wilshire Blvd, Los Angeles, California 90073, USA.
authors.forename: Tristan
authors.initials: T
authors.lastname: Shuman
authors.affiliation: 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.
authors.forename: Justin
authors.initials: J
authors.lastname: Shobe
authors.affiliation: Department of Neurosciences, University of California, San Diego, La Jolla, California 92093, USA.|Veterans Affairs Medical Center, San Diego, California 92161, USA.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Biane
authors.affiliation: 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.
authors.forename: Weilin
authors.initials: W
authors.lastname: Song
authors.affiliation: 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.
authors.forename: Brandon
authors.initials: B
authors.lastname: Wei
authors.affiliation: 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.
authors.forename: Michael
authors.initials: M
authors.lastname: Veshkini
authors.affiliation: 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.
authors.forename: Mimi
authors.initials: M
authors.lastname: La-Vu
authors.affiliation: Departments of Neurology and Psychiatry &Biobehavioral Sciences, Integrative Center for Learning and Memory, Brain Research Institute, University of California, Los Angeles, California 90095, USA.|West Los Angeles VA Medical Center, 11301 Wilshire Blvd, Los Angeles, California 90073, USA.
authors.forename: Jerry
authors.initials: J
authors.lastname: Lou
authors.affiliation: Departments of Neurology and Psychiatry &Biobehavioral Sciences, Integrative Center for Learning and Memory, Brain Research Institute, University of California, Los Angeles, California 90095, USA.|West Los Angeles VA Medical Center, 11301 Wilshire Blvd, Los Angeles, California 90073, USA.
authors.forename: Sergio E
authors.initials: SE
authors.lastname: Flores
authors.affiliation: 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.
authors.forename: Isaac
authors.initials: I
authors.lastname: Kim
authors.affiliation: 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.
authors.forename: Yoshitake
authors.initials: Y
authors.lastname: Sano
authors.affiliation: 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.
authors.forename: Miou
authors.initials: M
authors.lastname: Zhou
authors.affiliation: 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.
authors.forename: Karsten
authors.initials: K
authors.lastname: Baumgaertel
authors.affiliation: 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.
authors.forename: Ayal
authors.initials: A
authors.lastname: Lavi
authors.affiliation: Division of Hematology/Oncology, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Kamata
authors.affiliation: Department of Neurosciences, University of California, San Diego, La Jolla, California 92093, USA.|Veterans Affairs Medical Center, San Diego, California 92161, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Tuszynski
authors.affiliation: 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.
authors.forename: Mark
authors.initials: M
authors.lastname: Mayford
authors.affiliation: Departments of Neurology and Psychiatry &Biobehavioral Sciences, Integrative Center for Learning and Memory, Brain Research Institute, University of California, Los Angeles, California 90095, USA.|West Los Angeles VA Medical Center, 11301 Wilshire Blvd, Los Angeles, California 90073, USA.
authors.forename: Peyman
authors.initials: P
authors.lastname: Golshani
authors.affiliation: 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.
authors.forename: Alcino J
authors.initials: AJ
authors.lastname: Silva
mesh_terms: D000818:Animals; D056547:CA1 Region, Hippocampal / Q000166:cytology* / Q000502:physiology*; D002118:Calcium / Q000032:analysis; D005239:Fear; D008297:Male; D008568:Memory / Q000502:physiology*; D011939:Mental Recall / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology*; D013997:Time Factors
chemical_list: D002118:Calcium