Adolescent male Fmr1 KO and WT mice were treated with lithium for 4 weeks. After testing, lithium treatment was discontinued for 4 weeks and the mice were retested. Prior testing in the same paradigms had no effect on re-test performance in untreated WT mice or Fmr1 KO mice (Student's t-test, p>0.05 compared to retest; object novelty detection task: WT no treatment: n=7, t(12)=0.78, p>0.05; FX no treatment: n=9, t(16)=0.29, p>0.05; temporal ordering for objects task: WT no treatment: n=7, t(12)=0.68, p>0.05; FX no treatment: n=9, t(16)=1.42, p>0.05). (A,B) Performance in the object novelty detection task. (A) Times spent exploring the novel (N) and familiar (F) object. (Student's t-test; *p<0.05 compared to time spent with familiar object; WT no treatment: n=7, t(12)=3.78, p<0.05; WT discontinued lithium treatment: n=7, t(12)=3.57, p<0.05; Fmr1 KO no treatment: n=9, t(16)=1.87, p>0.05; Fmr1 KO discontinued lithium treatment: n=9, t(16)=2.28, p<0.05) (B) Exploration ratio. (one-way ANOVA followed by post hoc Bonferroni's multiple comparison test; F(3,28)=47.41). *p<0.05 compared to matched WT mice. (C,D) Performance in the temporal ordering for objects task. (C) Times spent exploring the first object presented (Object 5) and the object most recently explored (Object 7). (Student's t-test; *p<0.05 compared to time spent with Object 7; WT no treatment: n=7, t(12)=3.87, p<0.05; WT discontinued lithium treatment: n=9, t(12)=3.48, p<0.05; Fmr1 KO no treatment: n=9, t(16)=3.75, p<0.05; Fmr1 KO discontinued lithium treatment: n=9, t(16)=1.75, p>0.05). (D) Exploration ratio. (one-way ANOVA followed by post hoc Bonferroni's multiple comparison test; F(3,28)=28.80, p<0.05). *p<0.05 compared to matched WT mice.