Behavioral state-dependent episodic representations in rat CA1 neuronal activity during spatial alternation |
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Authors: | Muneyoshi Takahashi Johan Lauwereyns Yoshio Sakurai Minoru Tsukada |
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Institution: | (1) Tamagawa University Brain Science Institute, 6-1-1 Tamagawa-gakuen, Machida, Tokyo 194-8610, Japan;(2) School of Psychology, Victoria University of Wellington, Wellington, 6006, New Zealand;(3) Department of Psychology, Graduate School of Letters, Kyoto University, Kyoto 606-8501, Japan;(4) Japan Society for the Promotion of Science, Tokyo 102-8471, Japan;(5) Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Kawaguchi 332-0012, Japan |
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Abstract: | Hippocampus is considered crucial for episodic memory, as confirmed by recent findings of “episode-dependent place cells”
in rodent studies, and is known to show differential activity between active exploration and quiet immobility. Most place-cell
studies have focused on active periods, so the hippocampal involvement in episodic representations is less well understood.
Here, we draw a typology of episode-dependent hippocampal activity among three behavioral periods, presumably governed by
different molecular mechanisms: Active exploration with type 1 theta, quiet alertness with type 2 theta, and consummation
with large amplitude irregular activity. Five rats were trained to perform a delayed spatial alternation task with a nose-poke
paradigm and 12 tetrodes were implanted for single-unit recordings. We obtained 135 CA1 pyramidal cells and found that 75
of these fired mainly during active exploration, whereas 42 fired mainly during quiet alertness and 18 during consummation.
In each type of neuron, we found episode-dependent activity: 51/75, 22/42, and 15/18, respectively. These findings extend
our knowledge on the hippocampal involvement in episodic memory: Episode dependency also exists during immobile periods, and
functionally dissociated cell assemblies are engaged in the maintenance of episodic information throughout different events
in a task sequence. |
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Keywords: | Hippocampus Spatial alternation Memory Rat Nose-poke paradigm |
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