The hippocampus plays a selective role in the retrieval of detailed contextual memories.
BACKGROUND
It is widely believed that the hippocampus plays a temporary role in the retrieval of episodic and contextual memories. Initial research indicated that damage to this structure produced amnesia for newly acquired memories but did not affect those formed in the distant past. A number of recent studies, however, have found that the hippocampus is required for the retrieval of episodic and contextual memories regardless of their age. These findings are currently the subject of intense debate, and a satisfying resolution has yet to be identified.


RESULTS
The current experiments address this issue by demonstrating that detailed memories require the hippocampus, whereas memories that lose precision become independent of this structure. First, we show that the dorsal hippocampus is preferentially activated by the retrieval of detailed contextual fear memories. We then establish that the hippocampus is necessary for the retrieval of detailed memories by using a context-generalization procedure. Mice that exhibit high levels of generalization to a novel environment show no memory loss when the hippocampus is subsequently inactivated. In contrast, mice that discriminate between contexts are significantly impaired by hippocampus inactivation.


CONCLUSIONS
Our data suggest that detailed contextual memories require the hippocampus, whereas memories that lose precision can be retrieved without this structure. These findings can account for discrepancies in the literature-memories of our distant past can be either lost or retained after hippocampus damage depending on their quality-and provide a new framework for understanding memory consolidation.
Wiltgen
Brian J
BJ
Department of Psychology, University of Virginia, Charlottesville, VA 22904, USA.
Zhou
Miou
M
Cai
Ying
Y
Balaji
J
J
Karlsson
Mikael Guzman
MG
Parivash
Sherveen N
SN
Li
Weidong
W
Silva
Alcino J
AJ
D000818:Animals; D005260:Female; D015870:Gene Expression; D006624:Hippocampus / Q000502:physiology*; D016014:Linear Models; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL