Three-dimensional markerless motion capture of multiple freely behaving monkeys toward automated characterization of social behavior.

Given their high sociality and close evolutionary distance to humans, monkeys are an essential animal model for unraveling the biological mechanisms underlying human social behavior and elucidating the pathogenesis of diseases exhibiting abnormal social behavior. However, behavioral analysis of naturally behaving monkeys requires manual counting of various behaviors, which has been a bottleneck due to problems in throughput and objectivity. Here, we developed a three-dimensional markerless motion capture system that used multi-view data for robust tracking of individual monkeys and accurate reconstruction of the three-dimensional poses of multiple monkeys living in groups. Validation analysis in two monkey groups revealed that the system enabled the characterization of individual social dispositions and relationships through automated detection of eight basic social events. Analyses of social looking demonstrated its potential for investigating adaptive behaviors in a social group. These results suggest that this motion capture system will greatly enhance our ability to analyze primate social behavior.