Hippocampal granule cells opt for early retirement

Increased excitability and plasticity of adult‐generated hippocampal granule cells during a critical period suggests that they may “orthogonalize” memories according to time. One version of this “temporal tag” hypothesis suggests that young granule cells are particularly responsive during a specific...

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Published in:	Hippocampus Vol. 20; no. 10; pp. 1109 - 1123
Main Authors:	Alme, C.B., Buzzetti, R.A., Marrone, D.F., Leutgeb, J.K., Chawla, M.K., Schaner, M.J., Bohanick, J.D., Khoboko, T., Leutgeb, S., Moser, E.I., Moser, M.-B., McNaughton, B.L., Barnes, C.A.
Format:	Journal Article
Language:	English
Published:	Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-10-2010
Subjects:	Animals CA3 Region, Hippocampal - cytology CA3 Region, Hippocampal - physiology catFISH dentate gyrus Electroshock Environment, Controlled immediate early genes Male Memory - physiology Models, Neurological Neurogenesis - physiology Neuronal Plasticity - physiology Neurons - cytology Neurons - physiology place cells Rats Rats, Inbred F344 spatial behavior Time Factors
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Summary:	Increased excitability and plasticity of adult‐generated hippocampal granule cells during a critical period suggests that they may “orthogonalize” memories according to time. One version of this “temporal tag” hypothesis suggests that young granule cells are particularly responsive during a specific time period after their genesis, allowing them to play a significant role in sculpting CA3 representations, after which they become much less responsive to any input. An alternative possibility is that the granule cells active during their window of increased plasticity, and excitability become selectively tuned to events that occurred during that time and participate in later reinstatement of those experiences, to the exclusion of other cells. To discriminate between these possibilities, rats were exposed to different environments at different times over many weeks, and cell activation was subsequently assessed during a single session in which all environments were revisited. Dispersing the initial experiences in time did not lead to the increase in total recruitment at reinstatement time predicted by the selective tuning hypothesis. The data indicate that, during a given time frame, only a very small number of granule cells participate in many experiences, with most not participating significantly in any. Based on these and previous data, the small excitable population of granule cells probably correspond to the most recently generated cells. It appears that, rather than contributing to the recollection of long past events, most granule cells, possibly 90–95%, are effectively “retired.” If granule cells indeed sculpt CA3 representations (which remains to be shown), then a possible consequence of having a new set of granule cells participate when old memories are reinstated is that new representations of these experiences might be generated in CA3. Whatever the case, the present data may be interpreted to undermine the standard “orthogonalizer” theory of the role of the dentate gyrus in memory. © 2010 Wiley‐Liss, Inc.
Bibliography:	Natural Sciences and Engineering Research Council of Canada ark:/67375/WNG-HBNBG66X-H McKnight Brain Research Foundation istex:1D99E84992C595348B0A384FB868155BDC8C0B76 The Alberta Heritage Foundation for Medical Research Centre of Excellence Scheme of the Norwegian Research Council Kavli Foundation ArticleID:HIPO20810 C.B. Alme, R.A. Buzzetti, and D.F. Marrone contributed equally to this work. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1050-9631 1098-1063
DOI:	10.1002/hipo.20810