Long-term associative memory in rats: Effects of familiarization period in object-place-context recognition test.

Shota Shimoda,Takaaki Ozawa,Yukio Ichitani,Kazuo Yamada,Robert Sutherland

doi:10.1371/journal.pone.0254570

Shota Shimoda, Takaaki Ozawa + Show 3 more

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https://doi.org/10.1371/journal.pone.0254570

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Abstract

Spontaneous recognition tests, which utilize rodents' innate tendency to explore novelty, can evaluate not only simple non-associative recognition memory but also more complex associative memory in animals. In the present study, we investigated whether the length of the object familiarization period (sample phase) improved subsequent novelty discrimination in the spontaneous object, place, and object-place-context (OPC) recognition tests in rats. In the OPC recognition test, rats showed a significant novelty preference only when the familiarization period was 30 min but not when it was 5 min or 15 min. In addition, repeated 30-min familiarization periods extended the significant novelty preference to 72 hours. However, the rats exhibited a successful discrimination between the stayed and replaced objects under 15 min and 30 min familiarization period conditions in the place recognition test and between the novel and familiar objects under all conditions of 5, 15 and 30 min in the object recognition test. Our results suggest that the extension of the familiarization period improves performance in the spontaneous recognition paradigms, and a longer familiarization period is necessary for long-term associative recognition memory than for non-associative memory.

Highlights

Recognition memory is necessary to discriminate novel information from what is already known
Our results suggest that the extension of the familiarization period improves performance in the spontaneous recognition paradigms, and a longer familiarization period is necessary for long-term associative recognition memory than for non-associative memory
A one-way analysis of variance (ANOVA) showed that there was no significant difference in discrimination index (DI) between each condition

Summary

Introduction

Recognition memory is necessary to discriminate novel information from what is already known. Since animals have an innate tendency to respond to or explore novel stimuli, the habituation-dishabituation paradigm has been regarded as a useful behavioral test to assess recognition memory in various animal species including Aplysia [1], rodents [2], monkeys [3], and humans [4]. Researchers have evaluated rodents’ recognition memory using several types of spontaneous recognition tests. Spontaneous recognition tests have been used to evaluate simple non-associative recognition memory (e.g., object recognition test [2]) and more complex associative recognition memory (e.g., place recognition test [5]; object-context recognition test [6]; objectplace-context (OPC) recognition test [7]).

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