Brain Circuit Differences May Determine Your Place in a Social Hierarchy

Social rank isn't something that just appears in the animal kingdom. Humans also follow social hierarchy from an early age. Now, scientists have taken a look at non-human primates to learn a bit more about this ranking and have found that the hierarchies are actually linked to specific brain networks.

In order to learn a bit more about social ranking, the researchers examined 25 macaque monkeys. They determined their rank within their social hierarchy and then conducted non-invasive scans of their brain. Surprisingly, the scientists found that brain regions in one neural circuit are actually larger in more dominant animals.

So what brain regions are involved? It turns out that the regions composing this circuit are the amygdala, raphe nucleus and hypothalamus. Previous research has shown that the amygdala is involved in learning and processing social and emotional information. In contrast, the raphe and hypothalamus are involved in controlling neurotransmitters and neurohormones, such as serotonin and oxytocin.

That's not all the researchers found, though. In more subordinate animals, another circuit of brain regions called the striatum was larger. The striatum is known to play a complex role in learning the value of choices and actions. They also found that another set of brain regions correlated both with social status and the size of the animal's social group.

"This finding may reflect the fact that social status in macaques depends not only on the outcome of competitive social interactions but on social bonds formed that promote coalitions," said Matthew Rushworth, one of the researchers, in a news release. "The correlation with social group size and social status suggests this set of brain regions may coordinate behavior that bridges these two social variables."

Currently, scientists are unsure whether the brain differences are present at birth or arise from social differences. That said, the researchers plan to conduct further research to find that out. In addition, social status also changes over time and in different contexts.

"While we might be top-dog in one circle of friends, at work we might be more of a social climber," said MaryAnn Noonan, one of the researchers. "The fluidity of our social position and how our brains adapt our behavior to succeed in each context is the next exciting direction for this area of research."

The findings are published in the journal PLOS Biology.