Figure 1. (a) Social approach apparatus for assaying sociability in mice. The subject mouse begins in the empty center chamber of a three-chambered Plexiglas apparatus. A novel object, an inverted wire pencil cup, is placed in one side chamber. A novel mouse, who has not been in visual, olfactory, or tactile contact with the subject, is placed inside an identical wire control cup in the opposite side chamber. Over a 10-minute test session, the automated photocells and software score the amount of time the subject mouse spends in each of the three chambers. The number of entries into each compartment is simultaneously recorded as an internal control for general exploratory activity. Time spent engaged in bone fide social interactions with the novel mouse, and directed exploration of the novel object, are subsequently scored from digital videotapes of the session, by investigators uninformed of the genotype or treatment condition. Photograph by Dr Mu Yang, contributed by the author. (b) Social approach chamber time scores in adult Engrailed2 (En2) knockout mice. Normal sociability is defined as more time spent in the chamber with the novel mouse than in the chamber with the novel object, and more time spent sniffing the novel mouse than sniffing the novel object. Wild-type littermate controls and heterozygotes displayed normal sociability on the chamber time parameter, while En2 null mutants failed to display sociability on this parameter. Reproduced from reference 170: Brielmaier J, Matteson PG, Silverman JL, et al. Autism-relevant social abnormalities and cognitive deficits in engrai!ed-2 knockout mice. PLoSOne. 2012;7:e40914. (c) Social approach sniff time scores in adult En2 mice. Wild-type littermate controls and heterozygotes displayed normal sociability on the sniff time parameter, while En2 null mutants failed to display sociability on this parameter. Time spent sniffing the novel mouse is a more direct measure of social inter actions, and usually more sensitive to mutations. Reproduced from reference 170: Brielmaier J, Matteson PG, Silverman JL, et al. Autism-relevant social abnormalities and cognitive deficits in engrailed-2 knockout mice. PLoS One. 2012;7:e40914.