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Learn Mem. 2018 Mar 15;25(4):176-182. doi: 10.1101/lm.046946.117. Print 2018 Apr.

Mechanisms of critical period in the hippocampus underlie object location learning and memory in infant rats.

Author information

1
Center for Neural Science, New York University, New York, New York 10003, USA.
2
Neuroscience Institute, NYU Langone Medical Center, New York, New York 10016, USA.

Abstract

Episodic memories in early childhood are rapidly forgotten, a phenomenon that is associated with "infantile amnesia," the inability of adults to remember early-life experiences. We recently showed that early aversive contextual memory in infant rats, which is in fact rapidly forgotten, is actually not lost, as reminders presented later in life reinstate a long-lasting and context-specific memory. We also showed that the formation of this infantile memory recruits in the hippocampus mechanisms typical of developmental critical periods. Here, we tested whether similar mechanisms apply to a nonaversive, hippocampal type of learning. We report that novel object location (nOL) learned at postnatal day 17 (PN17) undergoes the typical rapid forgetting of infantile learning. However, a later reminder reinstates memory expression. Furthermore, as for aversive experiences, nOL learning at PN17 engages critical period mechanisms in the dorsal hippocampus: it induces a switch in the GluN2A/2B-NMDA receptor ratio, and brain-derived neurotrophic factor injected bilaterally into the dorsal hippocampus immediately after training results in long-lasting memory expression. We conclude that in infancy the hippocampus plays a necessary role in processing episodic and contextual memories, including nonaversive ones, and matures through a developmental critical period.

PMID:
29545389
PMCID:
PMC5855526
[Available on 2019-04-01]
DOI:
10.1101/lm.046946.117

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