Places and flavours: one-trial paired associate learning as a model of episodic-like memory in the rat

Abstract

The question of whether any non-human species displays episodic memory is controversial. Associative accounts of animal learning recognise that behaviour can change in response to single events, but this in no way obliges us to suppose that animals need, or are later able, to recall representations of such unique events at a different time and place. One reason for suspecting that certain species possess a memory system with episodic-like characteristics is that several learning tasks have been developed that, even though they do not meet strict ‘what, where and when’ criteria, have the ‘snap-shot’ character of this form of memory. These include the delayed matching to place task in the water maze. We now describe a new training protocol for one-trial paired associate learning in which rats are able to learn to associate a specific flavour of food (from a population of 30 flavours) with a particular location in space (up to 47 locations) in novel combinations that are only ever presented once. The animals display above chance performance very early in training. Encoding is shown to depend on the normal operation of hippocampal N-methyl- d-aspartate (NMDA) receptors, while memory retrieval requires the normal operation of hippocampal AMPA receptors.