Do non-human primates cooperate? Evidences of motor coordination during a joint action task in macaque monkeys

Humans are intensively social primates, therefore many of their actions are dedicated to communication and interaction with other individuals. Despite the progress in understanding the cognitive and neural processes that allow humans to perform cooperative actions, in non-human primates only few studies have investigated the ability to interact with a partner in order to reach a common goal. These studies have shown that in naturalistic conditions animals engage in various types of social behavior that involve forms of mutual coordination and cooperation. However, little is known on the capacity of non-human primates to actively cooperate in a controlled experimental setting, which allows full characterization of the motor parameters underlying individual action and their change during motor cooperation. To this aim, we analyzed the behavior of three pairs of macaque monkeys trained to perform solo and joint-actions by exerting a force on an isometric joystick, as to move an individual or a common cursor toward visual targets on a screen. We found that during cooperation monkeys reciprocally adapt their behavior by changing the parameters that define the spatial and temporal aspects of their action, as to fine tune their joint effort, and maximize their common performance. Furthermore the results suggest that when acting together the movement parameters that specify each actor's behavior are not only modulated during execution, but also during planning. These findings provide the first quantitative description of action coordination in non-human primates during the performance of a joint action task.