Performances of the negr1 ^−/− and wild-type mice in the object recognition and the contextual fear conditioning task. Novel object recognition and novel location recognition task were performed to measure the recognition memory of negr1 ^−/− mice. (A, left ) In the novel object recognition task, both the negr1 ^−/− and wild-type mice preferred the novel object (N) to the familiar object (F ) (paired t -test; negr1 ^−/−, t ₍₉₎=−2.65, p<0.05; wild-type, t ₍₉₎=−5.06, p<0.05). (A, right ) No differences between the two groups were found. (B) In the novel location recognition task, no differences between the two groups in the preference of new location and discrimination ratio were observed. (C) In the contextual fear conditioning task, no differences between the two groups in the freezing levels to context were found. *p<0.05; **p<0.01; n.s., not significant. Data are presented as mean±s.e.m.