Sex- and social context-dependent differences in mice fine head movement during social interactions.

Background: Social decision-making is influenced by multiple factors such as age, sex, emotional state, and the individual's social environment. While various behavioural readouts have been commonly used to study social behaviour in rodents, the role of fine head movements during social interactions remains underexplored despite the presence of accelerometers in many electrophysiological recording systems.

Results: Here, we used head acceleration data to analyse head movement kinematics in adult male and female mice across several social discrimination tests in various time scales. Our findings demonstrate the complementary nature of two variables derived from the raw acceleration, namely overall static (OSHA) and dynamic (ODHA) head acceleration, as well as specific head angles (Pitch and Roll). Together, these variables provide a comprehensive, detailed analysis of head movement, which cannot be easily achieved by video analysis systems such as DeepLabCut. Overall, our results suggest that head movement patterns are significantly influenced by sex, stimulus preference, and social context. Specifically, ODHA exhibited strong sex dependence and appeared to be more sensitive to internal states such as arousal and alertness. The static components were primarily influenced by social context, particularly stimulus preference, and seemed to reflect the subject's motivation to engage with the stimulus. The Roll angle also appeared strongly modulated by the broader social context.

Conclusions: Our study provides a novel method and analysis pipeline for studying the social behaviour of small rodents in high-time resolution using a head-based accelerometer. Our findings suggest that such measurements may inform the affective and motivational states of the subject during social interactions.