Episodic-like memory: rats remember when events occurred

Episodic memory refers to memories of unique past events, which are grounded in a temporal framework. It has recently been argued that episodic-like memory in rats may be 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. In this study, rats were tested in the morning and afternoon, on separate days. A distinctive flavor (chocolate) replenished at a daily-unique location at only one of these times. The retention interval between study and test was constant to render the how-long-ago cue irrelevant. Rats solved the task using time of day rather than using the cue of how long ago an event occurred. Two lines of evidence suggest that at the time of test, rats remembered the time at which the distinctive event occurred, similar to human episodic memory.