Figure 1.

Individual differences for cognitive aging in healthy rats. a Training trial performance for a group of young (6 months) and aged (28 months) male Long-Evans rats. Data points on the far left indicate performance on the first training trial, where no age difference was observed. The protocol consisted of three trials/day, with the last trial every other day consisting of a probe without the platform available for 30 s to monitor the rat’s spatial bias in searching for the platform location. b The learning index scores for individual rats in the young and aged groups obtained from probe trial performance to reflect search accuracy over the course of training. Note that the range of scores for aged rats encompasses and exceeds the range for the young, in the direction of impairment (higher index scores). c The retest scores from a probe trial after training 2 weeks later, with the platform in a new spatial location. In the re-test, data are presented for young rats and subgroups of aged rats based on the original learning index; aged rats that fell within the range of young performance are indicated as aged-unimpaired (AU), while aged rats that fell outside the range of young performance are designated impaired (AI). Aged rats that were impaired on the initial assessment were also impaired in the retest, while unimpaired aged rats again performed on a par with young. Note that the “search error” measure for training trials represents deviation from a direct path to the platform from the starting position, and that the learning index is calculated from probe trial search in X–Y coordinates (see Gallagher et al. 1993 for details). Data are reproduced from Colombo et al. 1997