Figure 1.

A, Aged beagles were cognitively assessed before treatment and matched into two groups with similar learning error scores. B, Spatial attention measured using a landmark discrimination task was not improved after two immunizations (Landmark 1) nor after 25 immunizations (Landmark Retest). C, Spatial attention measured using a variable distance procedure also did not reveal improvements in immunized dogs. D, On a measure of more complex learning ability, dogs receiving 12 immunizations showed no improvement on three phases of an oddity discrimination problem. E, Spatial learning of a two-choice delayed non-match-to-position task was equivalent in the two groups after up to 14 vaccinations, with all animals showing progressive improvements with repeated testing. F, The maximal memory score representing how long animals can remember spatial information also did not vary as a function of treatment. G, H, Spatial working memory assessed after eight immunizations (G) or 17 immunizations (H) also did not show significant treatment effects. Bars represent means, and error bars represent SEM.