Behavior during epochs of exploration. A, Object exploration time for adult and old rats during the two epochs of exploration. Object exploration was counted when a rat directed its nose toward an object while within 2 cm of it. Rats explored the five objects for significantly more time during behavioral epoch 1 relative to epoch 2 (repeated-measures ANOVA, F(1,20) = 24.8, p < 0.001), indicating that the rats recognized the objects as familiar during epoch 2. There was no significant difference in exploration time between rats assigned to the AA condition versus AB condition (ANOVA, F(1,20) = 0.13, p > 0.72). However, there was a significant main effect of age (repeated-measures ANOVA, F(1,20) = 6.68, p < 0.02), with the old rats spending less time exploring the objects. Error bars indicate ± 1 SEM. B, Number of threshold crossings for adult and old rats during the two epochs of exploration. There was no significant effect of epoch on threshold crossings (F(1,20) = 0.93, p = 0.35, repeated-measures ANOVA). Moreover, the number of threshold crossings did not significantly differ between behavioral conditions (AA vs AB; F(1,20) = 0.10, p = 0.76). On average, adult rats made a significantly greater number of threshold crossings than did old rats (F(1,20) = 13.73, p < 0.01). Error bars indicate ± 1 SEM.