In social preference (A), the % of the time 10-20 week old MRL/+ (10F/10M), MRL/lpr Fn14WT (10F/14M) and MRL/lpr Fn14KO (8F/13M) mice spend interacting with another mouse relative to an inanimate object is measured. In the object placement test (B), the relative preference of MRL/+, MRL/lpr Fn14WT and KO mice to explore a familiar object in a novel location was measured. At 10-20 weeks of age, the number of mice in the MRL/+, MRL/lpr Fn14WT and MRL/lpr Fn14KO groups were 5F/5M, 3F/7M, and 2F/6M, respectively. In mice 21-40 weeks of age, the number of mice in the MRL/+, MRL/lpr Fn14WT, and MRL/lpr Fn14KO groups were 9F/10M, 7F/7M, and 5F/6M, respectively. Only for the 10-20 week old mice in the object placement test were the MRL/+ mice tested at a different time than the MRL/lpr mice, for technical reasons. Otherwise, the MRL/+, MRL/lpr Fn14WT, and MRL/lpr Fn14KO mice groups had their neurobehavioral assessments done concurrently. In object recognition (C), the relative preference of MRL/lpr Fn14WT and KO mice to explore a novel object was measured. At 10-20 weeks of age, the number of mice in the MRL/+, MRL/lpr Fn14WT and MRL/lpr Fn14KO groups was 5F/5M, 8F/9M, and 6F/6M, respectively. In mice 21-40 weeks of age, the number of mice in the MRL/+, MRL/lpr Fn14WT, and MRL/lpr Fn14KO groups were 10F/10M, 7F/7M, and 4F/7M, respectively. The dotted line in panels A-C denotes normal (>50% preference).