(A) Schematic representation of the home-cage environment, and the time windows for behavioral analysis. (B) Images providing a representative illustration of huddling (left) and non-huddling (right) mice, as determined through manual behavioral annotation. Huddling was classified for incidents in which two mice were in bodily contact, resulting in no visible background between them, and this contact lasted for more than a second. Mice bodies included the abdomen and thorax but not the head, legs, paws, and tail. (C) Time devoted to different behaviors prior to sleep onset in a non-huddling state. n = 8 female and male mice. Paired t-tests, two tailed. ns, p > 0.05; *, 0.01 < p < 0.05; ***, 0.001 < p < 0.01. (D) Time devoted to different behaviors prior to sleep onset in a huddling state. n = 8 female and male mice. Paired t-tests, two tailed. ns, p > 0.05; *, 0.01 < p < 0.05; **, 0.001 < p < 0.01. (E) Proportion of time spent in huddling state during the 40-minute period preceding sleep onset. n = 8 female and male mice. Friedman test (p = 0.0002) followed by multiple comparisons: **, 0.001 < p < 0.01; ***, 0.0001 < p < 0.001.