Effect of age on object exploration, habituation, and response to spatial and nonspatial change

To measure their ability to detect novel arrangements in a given environmen t, young (6 months old) and senescent (22-24 months old) male F344 rats wer e repeatedly exposed to a given spatial configuration of objects contained in an open field. After the rats were habituated to the novel environment ( 1 trial with no objects, followed by 3 trials with 5 salient objects), the spatial arrangement of the objects was modified (2 trials), and object nove lty was tested (2 trials) by substituting a familiar object with a new one at the same location (nonspatial change). The results indicated that the se nescent rats explored old objects less than young rats, particularly on Tri al 2. On the Ist trial with displaced objects (Trial 5), the senescent rats explored the displaced objects less than the young rats. However, when a n ew object was placed in the field (Trials 7-8), there were no age differenc es in new object exploration. These results suggest that senescent rats hav e decrements in the ability to build spatial representations of the environ ment and to use this information to detect such changes, even though object recognition is not impaired with age.