Memory of Occasional Events in Rats: Individual Episodic Memory Profiles, Flexibility, and Neural Substrate

Abstract

In search for the mechanisms underlying complex forms of human memory, such as episodic recollection, a primary challenge is to develop adequate animal models amenable to neurobiological investigation. Here, we proposed a novel framework and paradigm that provides means to quantitatively evaluate the ability of rats to form and recollect a combined knowledge of what happened, where it happened, and when or in which context it happened (referred to as episodic-like memory) after a few specific episodes in situations as close as possible to a paradigm we recently developed to study episodic memory in humans. In this task, rats have to remember two odor-drink associations (what happened) encountered in distinct locations (where it happened) within two different multisensory enriched environments (in which context/occasion it happened), each characterized by a particular combination of odors and places. By analyzing licking behavior on each drinking port, we characterized quantitatively individual recollection profiles and showed that rats are able to incidentally form and recollect an accurate, long-term integrated episodic-like memory that can last Ն24 d after limited exposure to the episodes. Placing rats in a contextually challenging recollection situation at recall reveals the ability for flexible use of episodic memory as described in humans. We further report that reversible inactivation of the dorsal hippocampus during recall disrupts the animal's capacity to recollect the complete episodic memory. Cellular imaging of c-Fos and Zif268 brain activation reveals that episodic memory recollection recruits a specific, distributed network of hippocampal-prefrontal cortex structures that correlates with the accuracy of the integrated recollection performance.

Ultimate and proximate mechanisms of reciprocal altruism in rats

“…Recognition and long-term memory of individuals has been demonstrated in birds (Boeckle & Bugnyar, 2012;Godard 1991) and mammals (Bruck, 2013;Kendrick, da Costa, Leigh, Hinton, & Peirce, 2001), suggesting that this precondition for cooperation through direct reciprocity is met at least in these vertebrate taxa. Long-term memory has been demonstrated also in laboratory strains of Norway rats (Babb & Crystal, 2006;Veyrac et al, 2015) and in a number of other vertebrates (see Zentall, 2013, for review), and even invertebrates such as bees or fruit flies are capable of several forms of learning and memory, with neuronal mechanisms of learning appearing to be homologous to ours (Davis, 2005;Kawecki, 2010;Mery & Kawecki, 2002). Therefore, we think there is little reason to believe that reciprocal altruism can be expected only Bin species closely related to us, like apes and perhaps monkeys^due to the limited cognitive abilities of other animals, as has been argued (Zentall, 2016).…”

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

“…Indeed, although several tests have been developed to measure episodic-like memory in rodents, some of them are thought to be inappropriate for episodic-like memory tests. For example, a food reinforcement-based test (Veyrac et al 2015) is unlikely to meet the definition of episodic-like memory because it requires multiple training sessions. According to its definition, the test for episodic-like memory should be completed in a few training sessions.…”

A Novel Task for Studying Memory of Occasional Events in Rats

“…When the animal approaches a port, the http://www.bio-protocol.org/e1740 Vol 6, Iss 5, Mar 5, 2016 Copyright © 2016 The Authors; exclusive licensee Bio-protocol LLC. 6 corresponding camera is selected for signal acquisition. This allows us to save space occupied by the video files.…”

“…The protocol presented here is adapted from Veyrac et al (2015). This work was supported by CNRS, University Lyon 1, University Paris-Sud 11, and by grants from the "Agence Nationale de la Recherche" (ANR-2010-BLAN-1413-01) to SL and NR, from the "Fondation pour la recherche médicale" (FDT20140930863) to AG and from LABEX CORTEX (ANR-11-LABX-0042) to NR.…”

“…. Here, we propose and describe in details a novel protocol we recently used to test the ability of rats to form and recollect episodic-like memory of previously encountered occasional episodes (Veyrac et al, 2015). During these episodes, the animals are briefly exposed to sets of specific odor-drink associations (what happened) encountered in specific locations (where it happened) within different multisensory enriched environments (in which context/occasion it happened).…”