Previous training improves memory retention. At 9 months of age, experienced 3xTg-AD-H mice exhibit improved retention for the platform location at both 1.5 and 24 h after training (A). However, a more marked effect of training appeared at 12 months of age at which the 3xTg-AD mice exhibit no deficit at 1.5 h and are only impaired at 24 h (B), similar to 4-month-old 3xTg mice. By 15 months, however, previous training does not benefit memory because both experienced and naive 3xTg-AD mice are significantly impaired in both MWM probe trials (C). *p < 0.05 with respect to NonTg mice;^ϕp < 0.05 with respect to the corresponding experienced group.