Interpreting Neural Representations of Aged Animals

It is becoming more clear that normal age-related cognitive decline is characterized not so much by significant cell loss in memory-related brain structures like the hippocampus, but rather by a change in the functional organization of information processing of its neural elements. Conse-quently, investigations of the changes in neural plastic abilities of the aged brain represent an approach that could reasonably be expected to result in important advances in our understanding of age-related cognitive decline. To this end, the recent findings reported by Tanila et al. (1997) and Barnes et al. (1997) move the field forward in significant respects. The data presented in Tanila et al. (1997) suggest that hippocampal place fields of aged rats are remarkably stable across different environments, while Barnes et al. (1997) showed that a subset of hippocampal place fields of old rats represent spatial locations less reliably when animals are repeatedly tested across familiar environments. At first glance, these results appear in conflict. The recent commentary on this apparent discrepancy by Peter Rapp (1998