Boss Monkey
By Hannah Weisman, Behavioral Neuroscience, 2018
Could the human brain develop according to an individual’s social status? Someday, might scientists discover the particular formula, a unique blend of environment and genetics, that determines whether one is a leader, a follower, or somewhere in the middle? Neuroscientists have long considered the interplay between brain development and behaviors influencing social dominance in primates. Thus far, however, there has been a knowledge gap in understanding the neural mechanisms that may affect the social hierarchy of non-human primate groups.
In an effort to close this gap, scientists at the University of Oxford recently studied the brain scans and social patterns of 25 macaque monkeys to identify regions influencing social status. This study is significant because social hierarchy affects mental and physical health, as it determines access to resources and other factors influencing quality of life.
First, the team determined each monkey’s social standing by observing its behavior and then compared its actions to corresponding brain areas. Thus, the researchers were able to identify neural circuits in brain regions that suggest a direct relationship with social status — “one circuit in which gray matter volume tended to be greater in socially dominant individuals and another in which gray matter volume was greater in those with a more subordinate social position.”
In the dominant monkeys at the top of the social hierarchy, three specific brain areas tended to be larger: the amygdala, which regulates emotion and aggression; the hippocampus, which consolidates short-term and long-term memories; and the raphe nucleus, which releases serotonin.
Subordinate monkeys had enlarged regions in other areas of the brain, specifically within the striatum, which controls decision-making and movement pathways. Different areas of the brain were enlarged at either end of the social spectrum, indicating that dominance in the animal kingdom isn’t simply about aggression and having a larger brain. Instead, this evidence suggests dominance is also about forming social connections and making alliances within groups.
The results of the study do not indicate whether the differences in the monkeys’ brains were there from birth, predisposing one to a certain social position, or whether experiences shaped the brain’s organization. Most likely, these brain differences originate from an interaction of biological and sociological influences. Ultimately, this study suggests that primate brains, including perhaps human brains, can be specialized for life at either end of the social hierarchy.
This article was originally published in NUSci Issue 21.