Evidence for remembering when events occurred in a rodent model of episodic memory

Department of Psychology, University of Georgia, Athens, GA 30602-3013, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 06/2009; 106(23):9525-9. DOI: 10.1073/pnas.0904360106
Source: PubMed


The content of episodic memory consists of representations of unique past events. Episodic memories are grounded in a temporal framework (i.e., we remember when an event occurred). It has recently been argued that episodic-like memory in rats is qualitatively different from human episodic memory because, rather than remembering when an earlier past event occurred, rats used the cue of how long ago it occurred. We asked, therefore, whether rats remember the time of day at which they encountered a distinctive event, in addition to what occurred and where it happened. Rats were tested in the morning and afternoon, on separate days. A distinctive flavor (chocolate) was replenished at a daily-unique location at only one of these times. The interval between first and second daily opportunities to eat (study and test, respectively) was constant. Rats adjusted their revisits to the chocolate location at different times of day by using time of day rather than the cue of how long ago an event occurred. Two lines of evidence suggest that rats remembered the time at which the distinctive event occurred. First, under conditions in which the time of test (but not time of study) was novel, rats immediately transferred their knowledge of the chocolate contingency to the new test time. Second, under conditions in which predictions for study and test times were put in conflict, rats again used study time. Our results suggest that, at the time of memory assessment, rats remember when a recent episode occurred, similar to human episodic memory.

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    • "Roberts, Abroms, Kit, & Crupi, 2003; McKenzie, Bird, & Roberts, 2005) and many more recent successes (e.g., Babb & Crystal, 2005, 2006a, 2006b; Ferkin, Combs, delBarco-Trillo, Pierce, & Franklin, 2008; Naqshbandi, Feeney, McKenzie, & Roberts, 2007; Zhou & Crystal, 2009, 2011). Researchers have also struggled to find a bound what-where-when event memory in primates with some failures (e.g., Hampton, Hampstead, & Murray, 2005) and some recent success (e.g., Hoffman, Beran, & Washburn, 2009; Martin-Ordas, Haun, Colmenares, Call, 2010). "
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    • "The criterion for episodic-like memory is that a behavioral response should be based on "what" occurred "where" and "when" during a past experience (Clayton and Dickinson 1998; see also above). What–where–when memory as a form of episodic-like memory was first proposed in an elegant study on Western scrub jays (Clayton and Dickinson 1998) and later in rats (Zhou and Crystal 2009). Although the computational, cellular and neuroanatomical processes underlying spatial memory are often assumed also to control episodic memory (Buzsáki and Moser 2013), none of the traditional tests used in mice and rats assess episodic-like memory (Morris 2001). "
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