Episodic recollection in animals: “If it walks like a duck and quacks like a duck…”

In humans, episodic memory is most commonly defined as the subjective experience of recollection, presenting a major challenge to the identification of episodic memory in animals. Here we take the position that episodic memory also has several other distinctive qualities that can be assessed objectively in animals, as well as humans, and the examination of these properties provides insights into underlying mechanisms of episodic memory. We focus on recent evidence accumulated in this laboratory indicating that recognition in rats involves a threshold retrieval process, similar to that observed in human episodic recall. Also, rats can remember the temporal order of unique events, characteristic of the replay of vivid episodic memories in humans. Furthermore, rats combine elements of “when” and “where” events occur, as well as the flow of events within a memory, to distinguish memories that share overlapping features, also characteristic of human episodic memory. Finally, all of these capacities are dependent on the hippocampus, which also plays a critical role in human episodic memory. This combination of findings strongly suggests that animals have the same fundamental information processing functions that underlie episodic recall in humans.