GA vaccination counteracts cognitive decline in Tg-AD mice. Hippocampus-dependent cognitive activity was tested in the MWM. GA-vaccinated Tg-AD mice (diamonds; n = 6) showed significantly better learning/memory ability than untreated Tg-AD mice (squares; n = 7) during the acquisition and reversal phases but not the extinction phase of the task. Untreated Tg-AD mice showed consistent and long-lasting impairments in spatial memory tasks. In contrast, performance of the MWM test by the GA-vaccinated Tg-AD mice was rather similar, on average, to that of their age-matched naïve non-Tg littermates (triangles; n = 6) [three-way ANOVA, repeated measures: groups, df (2,16), F = 22.3, P < 0.0002; trials, df (3,48), F = 67.9, P < 0.0001; days, df (3,48), F = 3.1, P < 0.035, for the acquisition phase; and groups, df (2,16), F = 14.9, P < 0.0003; trials, df (3,48), F = 21.7, P < 0.0001; days, df (1,16), F = 16.9, P < 0.0008, for the reversal phase].