Introduction: Why studying social hierarchies in mice matters
Social hierarchies shape access to resources, mating opportunities, and territory in many species. While humans display complex social dynamics, the neural underpinnings that guide who becomes dominant or submissive remain a frontier of inquiry. A recent study from the Okinawa Institute of Science and Technology (OIST) sheds light on the brain circuits that drive social hierarchy in male mice, highlighting how past experiences influence future behavior and decision making.
How researchers mapped dominance in mice
To classify social standing, scientists used dominance tube tests. In these trials, two mice confront each other in opposite ends of a narrow tube; the more dominant individual secures the right of way, forcing the other to retreat. Repeating these encounters across days allowed researchers to identify which mice consistently emerged as dominant and which remained subordinate within their home groups.
Beyond individual tests, the team paired mice to examine how victories and losses reshaped social status. A dominant mouse in one cage might face a different outcome when paired with another dominant individual, revealing the dynamic nature of social hierarchies and the influence of prior experiences on future competitive success.
The loser effect: a brain-based explanation
Dr. Mao-Ting Hsu, the study’s lead author, explains that experience matters: those with a history of winning tend to become more dominant in subsequent encounters, while those with losses often slide in rank. The researchers probed the neural basis of this pattern and pinpointed a key player: cholinergic interneurons within the dorsomedial striatum, a region of the basal ganglia involved in behavioral flexibility and decision making.
Dissecting the role of cholinergic interneurons
Using selective cell removal techniques, the team disrupted cholinergic interneurons in the dorsomedial striatum and repeated the dominance tests. This manipulation specifically affected the loser effect: mice previously disadvantaged based on past losses did not exhibit the typical drop in dominance after losing experiences. In contrast, the winner effect remained largely unchanged, suggesting distinct circuits govern winning versus losing in social competition.
The findings imply that the loser effect is tied to flexible decision making under changing contexts, rather than a straightforward reward-based learning process. When mice confront different social or environmental scenarios, the altered activity of cholinergic interneurons appears to recalibrate their social behavior and hierarchy position.
What this means for our understanding of social behavior
The basal ganglia, and specifically the dorsomedial striatum, have long been linked to action selection and cognitive flexibility. This study adds a nuanced layer by showing that cholinergic interneurons help shape how losers adjust their status after negative social experiences. The winner effect, likely relying on reward circuits, seems to depend on a separate neural pathway. Together, these insights paint a more complex picture of how social hierarchies are negotiated in real time, rather than being driven solely by fixed traits like size or aggression.
Implications for human social dynamics
Although the study centers on male mice, the brain circuitry involved is conserved across mammals, including humans. Professor Jeffery Wickens notes that the architecture underlying flexible social decisions may share parallels with human social behavior, where dominance can shift across contexts—home, work, or social circles. While human dynamics are far more intricate, understanding the neural basis of winner and loser effects could illuminate the mechanisms that underlie social adaptability and context-dependent leadership.
Concluding thoughts
This research underscores that social hierarchy is not merely a product of physical prowess. Experiences and the brain’s learning and decision-making networks interact to shape who rises or falls in social standings. By isolating cholinergic interneurons in the dorsomedial striatum, scientists have opened new avenues for exploring how brains balance reward, risk, and context in social settings, with potential relevance to both animal welfare and human social science.
