Oral methylene blue treatment completely reverses behavioral impairment in PSAPP mice. Data were obtained from PSAPP mice treated with vehicle (PSAPP-V, n = 12) or with MB (PSAPP-MB, n = 12) and also wild-type mice treated with vehicle (WT-V, n = 12) or with MB (WT-MB, n = 12) for 3 months beginning at 15 months of age and subjected to behavioral testing at 18 months of age. A, locomotion (upper panel) and rearing (lower panel) scores obtained from open field activity testing are shown. B, recognition index (%) in the object recognition test is shown from training (upper panel) and retention test phases (lower panel). C, Y-maze test data are represented as total arm entries (upper panel) and spontaneous alternation (lower panel). D, 2-day radial arm water maze test data are shown with five blocks per day for errors (upper panel) and escape latency (lower panel). All statistical comparisons were performed among PSAPP-V, PSAPP-MB, WT-V, and WT-MB mice (*, p < 0.05; **, p < 0.01 for PSAPP-V versus PSAPP-MB, WT-V, and WT-MB mice).