Episodic-like memory in the rat

A fundamental question in comparative cognition is whether animals remember unique, personal past experiences [1-3]. It has long been argued that memories for specific events (referred to as episodic memory) are unique to humans [4,5]. Recently, considerable evidence has accumulated to show that food-storing birds possess critical behavioral elements of episodic memory [6-10], referred to as episodic-like memory in acknowledgment of the fact that behavioral criteria do not assess subjective experiences [1]. Here we show that rats have a detailed representation of remembered events and meet behavioral criteria for episodic-like memory. We provided rats with access to locations baited with distinctive (e.g., grape and raspberry) or nondistinctive (regular chow) flavors. Locations with a distinctive flavor replenished after a long but not a short delay, and locations with the nondistinctive flavor never replenished. One distinctive flavor was devalued after encoding its location by prefeeding that flavor (satiation) or by pairing it with lithium chloride (acquired taste aversion [11, 12]), while the other distinctive flavor was not devalued. The rats selectively decreased revisits to the devalued distinctive flavor but not to the nondevalued distinctive flavor. The present studies demonstrate that rats selectively encode the content of episodic-like memories.