Watching the watchers: aggression observation as a window into the neural mechanisms and computations underlying social learning.

Classic experiments by Albert Bandura more than 50 years ago first illustrated that aggression is shaped not just by innate predisposition but also by social learning. In this work, human observers "mirrored" aggressive behaviors after watching aggressive demonstrators, showing that observation can lead to action imitation. Beyond imitation of aggression itself, aggression observation may be critical for updating internal models of the social world and promoting adaptive behavioral states. As the tendency to watch aggression is both ubiquitous and conserved, this highly ethological behavior is a useful framework for understanding the neural mechanisms underlying social learning and behavioral refinement across species. Recent work has shown that the observation of aggression recruits widespread neural activity in subcortical brain regions that are known to be active during self-directed attack and learning during naturalistic behavior. This suggests that social learning of aggression might recruit systems for aggressive motivation, arousal, and reward in addition to traditional "action mirroring" systems. Unlike other forms of social learning with a single demonstrator, aggression observation represents a more complex form of social learning because the observed behavior consists of multiple demonstrators (a winner and loser) whose unique goals must be simultaneously inferred by the observer. Several recent computational approaches, including multiagent reinforcement learning and inverse reinforcement learning, are promising strategies for formalizing how individuals might update behavior following aggression observation.