Stability of social bonds over time: Measured in mice tested under semi-naturalistic conditions

From the first moments of life, social mammals become a part of a group. Over time they have “friends” with whom they prefer to spend time and “foes” whom they try to avoid. The ability to assess the dynamics of shifts in relationships is crucial to further our understanding of brain underpinnings of group behaviour. To investigate the stability of social bonds over time, we used groups of laboratory mice. Animals were kept in the fully automated, computer-controlled experimental environment (Eco-HAB) in which they could move freely and form social bonds. Eco-HAB system enables measuring the time each pair of mice within the group spends together voluntarily on each day, as reflected by the measure called in-cohort sociability. We used this measure to design the autocorrelation-based algorithm for the assessment of the stability of a social bond between any given two animals over time. We show that mouse dyads do not form stable relationships. Nonetheless, about 1/3 of the tested pairs developed constant level of spending time together. Additionally, we show that for all individual animals, the mean values of in-cohort sociability are very close to each other, which means that all animals form social bonds to the same extent, however, with different individuals. In summary, we present a cutting-edge computational approach to measuring the formation of social bonds in laboratory animals, as well as their stability over time. Its development constitutes a critical step forward in our ability to investigate the neural mechanisms of sociability in freely behaving animals.