Aging Ensembles: Circuit Contributions to Memory Deficits

This chapter reviews current knowledge about aged neural ensembles in the hippocampus and how alterations in the dynamics of these circuits are linked to memory decline. Topics discussed include fundamental properties of place cells in young and old rats, advanced age and the dynamic properties of hippocampal place cells, and memory decline. It is shown that old rats have notable differences in the dynamic properties of CA1 place fields, and several of these differences correspond with observed ageassociated behavioral deficits. Aged rats fail to show experience-dependent place field expansion plasticity to the same extent as young rats. Between episodes of experience in a single environment, aged rats are also impaired at maintaining stable spatial representations in the CA1 subregion of the hippocampus. This observation is consistent with the finding that old rats exhibit impaired performance on tasks requiring the solution of an allocentric spatial reference frame.