Scientists have identified the specific brain cells responsible for the “loser effect” in social hierarchies, revealing that losing experiences change dominance behaviour through distinct neural pathways separate from winning.
Researchers at the Okinawa Institute of Science and Technology found that cholinergic interneurons in the brain’s dorsomedial striatum control how animals become less dominant after losing competitions. The study, published in iScience, showed that removing these neurons disrupted the loser effect whilst leaving the winner effect unchanged, suggesting different brain mechanisms govern each response.
The research used dominance tube tests with male mice, where animals competed for right of way through narrow tubes. Scientists tracked how winning and losing altered each mouse’s position in their social hierarchy over multiple competitions. Mice that lost matches became measurably less dominant in subsequent encounters, whilst winners gained dominance.
“You may think that being dominant in the animal kingdom is all about physical attributes, like size. But interestingly, we’ve found that it seems to be a choice, based on previous experience,” said Professor Jeffery Wickens, head of the Neurobiology Research Unit at OIST and co-author of the study. “The brain circuitry involved in these decisions is well conserved between mice and humans, so there are likely useful parallels to be drawn.”
The basal ganglia region, previously known for its role in Parkinson’s Disease, regulates behavioural flexibility and decision-making. When researchers selectively removed cholinergic interneurons from this region, mice no longer decreased in dominance after losing, yet the winner effect remained intact.
Dr Mao-Ting Hsu, lead author, explained the findings suggest different learning processes underpin each effect. The winner effect appears to involve reward-based learning, whilst the loser effect operates through decision-making processes that adapt to different contexts.
“Human social dynamics are obviously far more complex. The boss in one household might be at the bottom of the social ranking at work, and dominance behaviour will change depending on the situation,” said Dr Hsu. “There is little evidence of the brain circuitry involved in these kinds of flexible social behaviours in humans. However, the similarities in brain structure between mice and humans mean these types of studies might help us unlock future insights into human social dynamics.”
The research focused exclusively on male mice, with the team noting that human social structures involve significantly more complexity than laboratory hierarchy tests.
