Shown are the mean ± SEM percentage correct for four aged and three young monkeys across baseline, the last two blocks of D₁ agonist treatment, and the post-D₁ period. Symbols indicate that performance under a particular condition differs significantly from another condition at an α-level of 0.05 as indicated by factorial ANOVA with Scheffe post hoc comparisons (^¥significant versus baseline; ^*significant versus D₁ agonist). Note: The blank space for monkey TYR under the D₁ agonist column reflects the fact that this monkey did not receive the final two blocks of treatment during the D₁ agonist testing period because of temporary illness. It is of note, however, that despite the abbreviated D₁ regimen in this ≥30-year-old monkey, significant improvement in spatial working memory was observed during the post-D₁ agonist testing period.