Hippocampus, ageing, and taste memories.

Previous studies have shown that ageing may induce deficits in hippocampal-dependent learning and memory tasks, the spatial task being most extensively applied in rats. It is proposed that taste learning and memory tasks may assist in understanding the ageing of memory systems, giving access to a more complete picture. Taste learning tasks allow us to explore a variety of learning phenomena in safe and aversive memories using similar behavioral procedures. In demanding the same sensory, response, and motivational requirements, this approach provides reliable comparisons between the performance of hippocampal lesioned and aged rats in different types of memory. Present knowledge on the effect of both ageing and hippocampal damage in complex taste learning phenomena is reviewed. Besides inducing deficits in hippocampal-dependent phenomena, such as blocking of conditioned taste aversion, while at the same time leaving intact nonhippocampal-dependent effects, such as latent inhibition, ageing is also associated with an increased neophobia by previous aversive taste memories and enhanced taste aversion conditioning which cannot be explained by age-related changes in taste or visceral distress sensitivity. In all, the results indicate a peculiar organization of the memory systems during aging that cannot be explained by a general cognitive decline or exclusively by the decay of the hippocampal function.