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.
Key study findings included:
- The area that signals an event's importance, called the ventral
striatum, responded to the prospect of a rise or fall in rank
as much as it did to the monetary reward, confirming the high
value accorded social status.
- Just viewing a superior human "player," as opposed to a perceived
inferior one or a computer, activated an area near the front
of the brain that appears to size people up — making interpersonal
judgments and assessing social status. A circuit involving the
mid-front part of the brain that processes the intentions and
motives of others and emotion processing areas deep in the brain
activated when the hierarchy became unstable, allowing for upward
and downward mobility.
- Performing better than the superior "player" activated areas
higher and toward the front of the brain controlling action planning,
while performing worse than an inferior "player" activated areas
lower in the brain associated with emotional pain and frustration.
- The more positive the mood experienced by participants while
at the top of an unstable hierarchy, the stronger was activity
in this emotional pain circuitry when they viewed an outcome
that threatened to move them down in status. In other words,
people who felt more joy when they won also felt more pain when
they lost.
"Such activation of emotional pain circuitry may underlie a heightened
risk for stress-related health problems among competitive individuals," suggested
Meyer-Lindenberg.
In collaboration with other NIMH researchers, Zink and colleagues
are planning follow-up studies to explore brain activity in response
to the experimental social hierarchy in patients with mental illnesses
like schizophrenia or autism, which are marked by social and thinking
deficits. The researchers will also be exploring whether particular
gene variants might differentially affect brain responses in similar
experiments.
Also participating in the study were Yunxia Tong, Qiang Chen,
Danielle Bassett, and Jason Stein, NIMH.
Cover art.
Brain activity was much higher in key brain centers when participants viewed a superior player in an unstable social hierarchy — when participants had the possibility of upward mobility.
Source: Caroline Zink, Ph.D., NIMH Genes Cognition and Psychosis Program
When participants experienced an outcome that could increase their status and have them become superior players, activity increased in circuitry at the top front of the brain that controls the intention to do something, suggesting that rising in a hierarchy makes one more action-oriented.
Source: Caroline Zink, Ph.D., NIMH Genes Cognition and Psychosis Program
As they played games in the MRI scanner, pictures with rankings of other players and updated outcomes periodically flashed on the screen. Situations that could signal a fall in status activated circuitry known to process emotional pain and frustration.
Source: Caroline Zink, Ph.D., NIMH Genes Cognition and Psychosis Program
The National Institute of Mental Health (NIMH) mission is to reduce the burden of mental and behavioral disorders through research on mind, brain, and behavior. More information is available at the NIMH website.
The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov.
References:
Zink CF, Tong Y, Chen Q, Bassett D, Stein JL, Meyer-Lindenberg
A. Know your place: neural processing of social hierarchy in humans. Neuron.
2008 Apr 24. Sapolsky RM. The influence of social hierarchy on primate health. Science.
2005 Apr 29;308(5722):648-52. Review. PMID:
15860617 Marmot MG. Status syndrome: a challenge to medicine. JAMA.
2006 Mar 15;295(11):1304-7. No abstract available. PMID: 16537740
|