While some people may enjoy categorizing their friends and family as either “alphas” or “betas,” other people believe such descriptions, though accurate when speaking of dogs and animals, are complete hooey when applied to humans. After all, each of us leads in certain ways within a group, while following in other ways. Besides, people fluidly move among a variety of social groups with a different status in each, and a status that changes over time in each. No matter how you see it, a new study from Oxford has found a link between social status and brain structure — at least in macaque monkeys. For dominant monkeys, some brain regions appeared to be larger and better connected than the same regions in subordinate peers, while other brain regions were smaller and less connected.

“Social status is an important feature of group life in many primates,” wrote the authors in their study. “Discovering how the brain is organized with respect to individual social status is an important first step for understanding the neural mechanisms that might drive social status and mediate its consequences.”

Brain Regions and Social Behavior

A team of researchers, led by Dr. MaryAnn Noonan of the Decision and Action Laboratory at the University of Oxford, hypothesized that social status in primates might be related to individual variation in subcortical brain regions — the deeper more primitive regions of the brain below the outer layer (the cerebral cortex), the regions implicated in social and emotional behavior. To investigate their theory, the team of researchers used magnetic resonance imaging (MRI) to look more closely at brain structure and brain function in 25 group-living macaque monkeys. But before they scanned any brains, the researchers first determined each monkey’s position within the social hierarchy of the group.

What did they discover? One circuit of brain regions — the amygdala, raphe nucleus, and hypothalamus — was larger and more connected in the dominant animals. Previous studies have shown the amygdala to be involved in learning (and processing) social and emotional information, while the raphe nucleus and the hypothalamus are known to control neurotransmitters and neurohormones, including serotonin and oxytocin, both of which influence mood. The MRI scans also revealed another circuit of brain regions, collectively called the striatum, appeared larger and better connected in the more subordinate animals. The striatum, past research has shown, plays a significant role in learning the value of our choices and actions.

"One possibility is that the demands of a life in a particular social position use certain brain regions more frequently and as a result those areas expand to step up to the task,” Noonan said. “Alternatively, it is possible that people born with brains organised in a particular way tend towards certain social positions.” Ultimately, she and her co-authors suggest both natural endowment and life experience may work together to produce behavior appropriate to social context. Our brains modify our reality, yet our reality also modifies our brains.

Source: Noonan MAP, Sallet J, Mars RB, et al. A Neural Circuit Covarying with Social Hierarchy in Macaques. PLOS Biology. 2014.