A part of the brain called the parahippocampal gyrus is involved in this social sorting. It helps us do something called "contextual processing" -- basically, figuring out where something or someone fits into our world. Another brain region, the dorsolateral prefrontal cortex, also helps us interpret rank.
In another version of the experiment, the researchers made it possible for players to move up or down in the rankings. When people thought they could gain higher status, new areas of the brain came into play.
Some of these areas are involved in preparing for movement. Even though the volunteers weren't really going to get up and do anything, the brain seemed to be getting ready for that climb up the social ladder.
One way to think about it, said Zink, is that "they prepare more, show more motivation, based on these activations. It's sort of, 'I'm going to beat you.'"
In an attempt to find out whether the study results were due more to competitive nature than an evaluation of social rankings, researchers set up a third experiment.
This time people knew the other players weren't real. They still were given rankings, but they knew they were playing against a computer. It turned out that some parts of the brain tuned in only when volunteers were comparing themselves to other humans.
Dr. Andreas Meyer-Lindenberg, one of the study's authors, pointed out that humans aren't the only animals who pay attention to social status.
Social rankings probably "existed long before consciousness or humankind, and I think they are embedded in brain and the architecture that shapes it," Meyer-Lindenberg said in an e-mail. That doesn't mean brain circuits cause those social rankings, but that we're built to recognize and act on them.
"Social hierarchies change," said Dr. David Amodio, an assistant professor of psychology at New York University who did not take part in the research. "This work shows how different mental systems come online to support the different challenges and goals associated with superior or inferior members of the group."
Zink hopes the study will help lay the groundwork for future research.
"We've all seen someone act inappropriately," she said, referring to how others might misbehave at work, with friends or at school. "Hierarchies are so important to every decision we make and all behaviors. And this is the first time we've been able to look at how the brain processes this information."
Some illnesses, such as autism, schizophrenia and depression, include misinterpreting or failing to recognize where we "fit" in our social world.
Zink said she hopes knowing how the brain processes social ranking will help shed light on these and other conditions.