Social fear and avoidance were assessed using the modified open-field system . Briefly, two 9 cm × 9 cm mesh enclosures were placed at the opposite sides of the open field. One enclosure contained a novel KM mouse as the social target, and another enclosure did not contain a mouse as the social un-target. The experimental mouse was allowed to freely explore a 50 cm × 50 cm arena containing the target and un-target enclosures. The time spent on the social interaction zone (14 cm × 26 cm) surrounding the target enclosure and the reference zones (14 cm × 26 cm) surrounding the un-target enclosure was measured using a video tracking system (TM-vision, Chengdu Techman Software Co., Ltd., Chengdu, China).