The "Hard-wired" pecking order 32

Human Brain Appears "Hard-Wired" for Hierarchy

Scans Hint at Why It Can be Unhealthy Even at the Top

Human imaging studies have for the first time identified brain circuitry associated with social status, according to researchers at the National Institute of Mental Health (NIMH) of the National Institutes of Health. They found that different brain areas are activated when a person moves up or down in a pecking order — or simply views perceived social superiors or inferiors. Circuitry activated by important events responded to a potential change in hierarchical status as much as it did to winning money.

"Our position in social hierarchies strongly influences motivation as well as physical and mental health," said NIMH Director Thomas R Insel, M.D. "This first glimpse into how the brain processes that information advances our understanding of an important factor that can impact public health."

Caroline Zink, Ph.D., Andreas Meyer-Lindenberg, M.D., Ph.D., and colleagues of the NIMH Genes Cognition and Psychosis Program, report on their functional magnetic resonance imaging (fMRI) study in the April 24, 2008, issue of the journal Neuron. Meyer-Lindenberg is now director of Germany's Central Institute of Mental Health.

Prior studies have shown that social status strongly predicts health. Animals chronically stressed by their hierarchical position have high rates of cardiovascular and depression/anxiety-like syndromes. A classic study of British civil servants found that the lower one ranked, the higher the odds for developing cardiovascular disease and dying early. Lower social rank likely compromises health through psychological effects, such as by limiting control over one's life and interactions with others. However, in hierarchies that allow for more upward mobility, those at the top who stand to lose their positions can have higher risk for stress-related illness. Yet little is known about how the human brain translates such factors into health risk.

To find out, the NIMH researchers created an artificial social hierarchy in which 72 participants played an interactive computer game for money. They were assigned a status that they were told was based on their playing skill. In fact, the game outcomes were predetermined and the other "players" simulated by computer. While their brain activity was monitored by fMRI, participants intermittently saw pictures and scores of an inferior and a superior "player" they thought were simultaneously playing in other rooms.

Although they knew the perceived players' scores would not affect their own outcomes or reward — and were instructed to ignore them — participants' brain activity and behavior were highly influenced by their position in the implied hierarchy.

"The processing of hierarchical information seems to be hard-wired, occurring even outside of an explicitly competitive environment, underscoring how important it is for us," said Zink.

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