Fig. 2.

Huddling behavior develops at the beginning of the second postnatal week, whereas primitive reflexes and motor and sensory functions develop earlier. a Representative images showing the primitive reflexes and motor and sensory functions, which are color-coded as described in b. b Developmental indexes for primitive reflexes (light gray) and motor (dark gray) and sensory functions (black) (N = 80 animals from 8 litters). c Representative images of huddling behavior of animals of different ages when experimental sessions ended. Black arrowheads indicate individual clusters. d Quantification of the average litter values ± SEM for the three parameters (time spent together, no. of different clusters, and no. of cluster switches), see the methods for the quantification of huddling behavior. Left panel: Kruskal–Wallis test, χ²₍₂₎ = 16.3, P < 0.001, post hoc Dunn’s test with Holm’s correction; middle panel: one-way ANOVA, F_(1,22) = 22.8, P < 0.001, pairwise t-test comparisons with Holm’s correction; right panel: type II ANOVA of ranks, F_(1,22) = 13.2, P < 0.001, h3-corrected. Top inset: average values and single litter data point for P7–9 of the data below. *P < 0.05 and ***P < 0.001. Tests shown in b and d were performed on the same set of animals