Reactivation of Neural Ensembles during the Retrieval of Recent and Remote Memory

Episodic memories are encoded within hippocampal and neocortical circuits. Retrieving these memories is assumed to involve reactivation of neural ensembles that were established during learning. Although it has been possible to follow the activity of individual neurons shortly after learning, it has...

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Bibliographic Details
Published in:Current biology 2013-01, Vol.23 (2), p.99-106
Main Authors: Tayler, Kaycie K., Tanaka, Kazumasa Z., Reijmers, Leon G., Wiltgen, Brian J.
Format: Article
Language:English
Subjects:
amygdala
Amygdala - physiology
Animals
Conditioning (Psychology)
cortex
doxycycline
fearfulness
Female
gene expression
Green Fluorescent Proteins
hippocampus
Hippocampus - physiology
Male
memory
Mental Recall - physiology
Mice
Mice, Transgenic
neocortex
Neocortex - physiology
Nerve Net - physiology
neurons
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Summary:Episodic memories are encoded within hippocampal and neocortical circuits. Retrieving these memories is assumed to involve reactivation of neural ensembles that were established during learning. Although it has been possible to follow the activity of individual neurons shortly after learning, it has not been possible to examine their activity weeks later during retrieval. We addressed this issue by using a stable form of GFP (H2B-GFP) to permanently tag neurons that are active during contextual fear conditioning. H2B-GFP expression in transgenic mice was increased by learning and could be regulated by doxycycline (DOX). Using this system, we found a large network of neurons in the hippocampus, amygdala, and neocortex that were active during context fear conditioning and subsequent memory retrieval 2 days later. Reactivation was contingent on memory retrieval and was not observed when animals were trained and tested in different environments. When memory was retrieved several weeks after learning, reactivation was altered in the hippocampus and amygdala but remained unchanged in the cortex. Retrieving a recently formed context fear memory reactivates neurons in the hippocampus, amygdala, and cortex. Several weeks after learning, the degree of reactivation is altered in hippocampal and amygdala networks but remains stable in the cortex. ► Neurons active during learning can be tagged with a stable form of GFP ► Tagged neurons in hippocampus and cortex are reactivated 2 days after learning ► Reactivation is stable in cortex but changes in hippocampus 2 weeks after learning
ISSN:0960-9822
1879-0445
DOI:10.1016/j.cub.2012.11.019