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.
An
image of Cover art: hierarchy and brain is available at <http://nimhcpeaktst.nimh.nih.gov/images/news-items/zinkcoverart3mb-2.jpg>.
Cover
art.
An
image of Unstable vs. stable hierarchy is available at <http://nimhcpeaktst.nimh.nih.gov/images/news-items/zinksuperior-inferior_brains-2.jpg>.
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
An
image of Action centers activated is available at <http://nimhcpeaktst.nimh.nih.gov/images/news-items/zinkriseinstatus_brain-2.jpg>.
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
An
image of Other players' pictures is available at
<http://nimhcpeaktst.nimh.nih.gov/images/news-items/zinkswdl_outcome_screen-2.jpg>.
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 -- is comprised of 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 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. < http://www.ncbi.nlm.nih.gov/pubmed/15860617?ordinalpos=26&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
> The influence of social hierarchy on primate health. "Science".
2005 Apr 29;308(5722):648-52. Review. PMID: 15860617
Marmot MG. < http://www.ncbi.nlm.nih.gov/pubmed/16537740?ordinalpos=4&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
> Status syndrome: a challenge to medicine. "JAMA".
2006 Mar 15;295(11):1304-7. No abstract available. PMID: 16537740
This NIH News Release is available online at:
<http://www.nih.gov/news/health/apr2008/nimh-23.htm>.