Episodic memory in animals: remembering which occasion.

Episodic memory, the recollection of past events in one's life, has often been considered a memory specific to humans. Recent work in a variety of species has challenged this view, and has raised important questions about the nature of episodic memory itself. We present a review of the types of task proposed as episodic-like in animals and consider that these tasks require animals to demonstrate memory for specific occasions in the past. We propose that identifying episodic memory as the memory for what happened where on a specific occasion is a more encompassing definition than one that relies on information about when an event occurred. These episodic-like tasks in animals support the view that the hippocampal system is necessary for episodic memory, and that the neural substrates of episodic memory can be dissociated from those of other forms of declarative memory.