The spatial selectivity of hippocampal neurons suggests that they contribute to an internal representation of current location. The activity of hippocampal pyramidal cells was recorded while adult (10-13 months old) and aged (24-28 months old) rats performed a task in which two spatial reference frames were put in conflict. Rats attempted to find an unmarked goal whose position was fixed relative to only one of the two reference frames. The ability of a rat's hippocampus to adjust to the conflicting information and use the 'correct' position estimate (hippocampal map 'realignment') was correlated with the rat's ability to find the hidden goal. In addition, aged rats were impaired relative to adult rats in both goalfinding accuracy and map realignment. Thus, changes in the effectiveness with which the hippocampal spatial representation is updated on the basis of external cues may contribute to both within-age-group spatial learning variability and agerelated spatial learning deficits.
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The authors thank J. Bohanick, J. Gerrard, S. de Dios, J. Dees, J. Yuan, K. Hardesty, N. Insel, J. Meltzer, J. Wang and K. Weaver-Sommers for help running experiments and processing data. This research was supported by Public Health Service grants AG12609, AG05805 and MH01565.