Episodic-like memory in purebred and crossbred Yucatan minipigs (Sus scrofa)

Abstract

Episodic memory is a human ability that involves mental re-creation of a personally experienced past event. Its existence is controversial in animals because it requires demonstration of self-consciousness and mental time travel. Episodic-like memory (simultaneous recall of what, where, when aspects of a past event) has been demonstrated in non-humans and appears to depend on the hippocampus. We explored the potential for episodic-like memory in pigs, a previously un-studied species reported to have high mental capacity. As was done for rats, we adopted a definition of episodic-like memory that equates recall of time ("when") with recall of context ("which"). We tested pigs' ability to remember what (object), where (location) and which (context). Through novel object recognition, pigs identified the less familiar of two object/location/context configurations. Since configuration familiarity differed only if all aspects were remembered simultaneously, we concluded that pigs were able to recall what/where/which, providing evidence of episodic-like memory.