Lithium was administered for four weeks to adult (from 8 to 12 weeks of age) and adolescent (from 4 to 8 weeks of age) male Fmr1 knockout (KO) and wild-type (WT) mice prior to testing. (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=20, t(46)=6.51, p<0.05; WT adult lithium treatment: n=10, t(18)=4.29, p<0.05; WT adolescent lithium treatment: n=9, t(10)=3.47, p<0.05; Fmr1 KO no treatment: n=20, t(48)=1.42, p>0.05; Fmr1 KO adult lithium treatment: n=10, t(18)=6.20, p<0.05; Fmr1 KO adolescent lithium treatment: n=9, t(16)=4.19, p<0.05). (B) Exploration ratio. (two-way ANOVA (genotype x treatment) followed by post hoc Bonferroni's multiple comparison test; F(2,72)=33.02, p<0.05; **p<0.05 compared to untreated WT mice; *p<0.05 compared to same genotype without treatment).