a | The testing arena, a clean, empty mouse cage. Each mouse was given a 10-minute habituation period in the empty cage, then scored for 10 minutes for cumulative time spent grooming all body regions81,90,111. b | Representative data in juvenile and adult male C57BL/6J (B6) mice and BTBR T+tf/J (BTBR) mice. High levels of repetitive self-directed grooming were evident in 18-, 28-, 38- and 60-day-old male BTBR mice compared with age-matched male B6 mice. n = 10 B6 mice and 10 BTBR mice. *p < 0.05. **p < 0.01. Part b is reproduced, with permission, from Ref. 81 © (2008) Blackwell Publishing.