Understanding the Neural Foundations of Social Hierarchies and Behavior

Social hierarchies are a fundamental aspect of both human societies and the animal kingdom, influencing access to resources, mating opportunities, and social influence. While many assume physical attributes determine dominance, recent research highlights the significant role of brain circuitry in shaping social rank. A study published in iScience by researchers at the Okinawa Institute of Science and Technology (OIST) delves into the neural mechanisms underlying social dominance and submission.

Using mice as models, scientists employed dominance tube tests to assess social standings within groups. In these tests, two mice are placed at opposite ends of a tube, and the one that pushes past the other is deemed dominant. Repeatedly, these tests established a consistent hierarchy, enabling researchers to identify dominant and subordinate mice.

Subsequently, mice from different cages competed against each other, and their behaviors reflected how previous wins or losses affected future interactions. The phenomenon known as the "winner effect" increases dominance after victories, while the "loser effect" diminishes it following defeats. The key focus was on the brain's cholinergic interneurons within the dorsomedial striatum, an area associated with behavioral flexibility.

The research revealed that these interneurons are crucial in mediating the loser effect. When scientists selectively removed these neurons, mice no longer exhibited reduced dominance after losing, indicating that this specific neural circuit is involved in processing defeat and adapting social behavior accordingly. Interestingly, the same neural pathways did not influence the winner effect, suggesting different brain mechanisms govern winning and losing in social contexts.

The basal ganglia, a brain region well-known in Parkinson’s disease, also play a role in social decision-making. It helps animals adapt their behaviors based on environmental cues, with the cholinergic interneurons being pivotal for decision-making in losing scenarios. The findings imply that losing in social situations involves complex decision-making processes, not just reward-based learning.

While these studies focused on male mice, they offer insight into potential parallels in human social dynamics. Human hierarchies are often more fluid, influenced by situational factors and individual experiences. Nevertheless, the conserved brain structures between mice and humans suggest that understanding these neural pathways could eventually inform us about social behavior and adaptability in humans.

In essence, this research emphasizes that social hierarchy is not solely dictated by physical characteristics but is significantly influenced by specific neural circuits that govern responses to social victories and defeats. Unlocking these mechanisms may pave the way for better understanding social behaviors and disorders related to social cognition.