Figure 2. Automated three-chambered social approach.

a | The test apparatus, a rectangular, three-chambered box made of clear polycarbonate^{44,81,82,83,90,91,109,111}. Retractable doorways built into the two dividing walls control access to the side chambers. Entries into each chamber are automatically detected by photocells embedded in the doorways. The number of entries and time spent in each chamber are tallied by the software. The test session begins with a 10-minute habituation session in the centre chamber only, followed by a 10-minute habituation session with access to all 3 empty chambers. If an innate side preference for either the right or left chamber is detected during the habituation session, the testing environment is reorganized to equalize light levels, nearby objects, and so on. The subject is then briefly confined to the centre chamber while a novel object (an inverted stainless steel wire pencil cup) is placed in one of the side chambers. A novel mouse, previously habituated to the enclosure, is placed in an identical wire cup located in the other side chamber. A weighted plastic cup is placed on the top of each inverted wire cup to prevent the subject from climbing on top. The side chambers containing the novel object and the novel mouse are alternated between left and right across subjects. After the novel object and the novel mouse are positioned, the two side doors are simultaneously lifted and the subject is allowed access to all three chambers for 10 minutes. In addition to the automatically tallied time spent in each chamber and entries into each chamber, an observer with stopwatches scores the time spent sniffing the novel object and the novel mouse, in real time or from videotapes. The investigator scoring time spent sniffing is blind to the identity of the subject mice. b | Adult male C57BL/6J (B6) and FVB/Ant mice displayed sociability, defined as spending more time in the chamber containing the novel mouse than in the chamber containing the novel object, and more time sniffing the novel mouse than sniffing the novel object. Adult male BTBR T+tf/J (BTBR) mice did not display sociability, spending similar amounts of time in the chamber containing the novel mouse and in the chamber containing the novel object, and similar amounts of time sniffing the novel mouse and sniffing the novel object, as previously reported in Refs 81,83,90,91,111. n = 12 B6 mice, 16 FVB/Ant mice and 12 BTBR mice. *p < 0.01 for the comparison between novel mouse and novel object.