Spatial memory impairments of negr1 ^−/− mice. To assess the spatial memory of the negr1 ^−/− mice, the Morris water maze task was conducted. (A) The negr1 ^−/− mice were slower in finding the hidden platform (ANOVA with a repeated measure; Group, F _(1,19)=5.13, p<0.05; Training = F _(7,133)=17.94, p<0.001, Group x Training, F _(7,133)=0.96, p=0.46). (B) No differences between the two groups were found in swimming speed during the place training. (C, D) The negr1 ^−/− mice exhibited less spatial bias than the wild-type mice on the probe trial (independent t -test; proximity, t ₍₁₉₎=−2.36, p<0.05; Target quadrant, t ₍₁₉₎=1.78, p=0.10). *p<0.05; n.s., not significant. Data are presented as mean±s.e.m.