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Brain structure associated with fear
inhibition also may influence personality
BOSTON - November 28, 2005 - The relationship between the
size of a brain structure and the ability to recover from traumatic
experiences also may influence overall personality type, according
to a study from Massachusetts General Hospital (MGH) researchers.
In a followup to earlier findings that an area of the brain called
the medial orbitofrontal cortex (mOFC) appears thicker in those
who can better control their emotional response to unpleasant memories,
the investigators found that study participants who exhibited better
fear inhibition also score higher in measures of extraversion -
an energetic, outgoing personality. The report appears in the Nov.
28 issue of NeuroReport.
"Some studies have demonstrated links between extraversion
or the trait of neuroticism and the overall activity of brain regions
that include the mOFC. But this is the first time anyone has looked
at the potential relation of both brain structure and fear extinction
to personality traits," says Mohammed Milad, PhD, of the MGH
Department of Psychiatry, a co-lead author of the study.
Most individuals initially respond with physical and emotional distress
to situations that bring back memories of traumatic events, but
such responses usually diminish over time, as the situations are
repeated without unpleasant occurrences. The ability to suppress
those negative responses is called "extinction memory,"
and its deficiency may lead to anxiety disorders such as post-traumatic
stress disorder.
In their
previous study, the MGH team focused on the ventromedial prefrontal
cortex - an area on the lower surface of the brain that includes
the mOFC and is believed to inhibit the activity of the amygdala,
a structure known to be involved with fear. The current report combined
the data analyzed in that study - published in the July 26, 2005,
Proceedings of the National Academy of Science - with the
results from a standard personality test. Since earlier research
has associated levels of extraversion and neuroticism - oversensitivity
and emotional instability - with vulnerability to anxiety disorders,
the current experiment focused on those traits.
As described in the PNAS study, over two days 14 study participants
viewed a series of digital photos that featured lamps with either
a red or a blue light shining. On the first day, participants viewed
the photos several times with a mild electric shock - described
as annoying but not painful - delivered to their hands after one,
but not the other, colored light appeared. They then viewed the
photos again with no shocks administered. On the second day, participants'
anxiety levels, determined by perspiration on the palm of the hand,
were measured while they once again viewed the photos with both
colors displayed but no shocks given. Structural magnetic resonance
(MR) images of the volunteers' brains showed that those who responded
with less anxiety on the second day also had a thicker mOFC, and
no other areas of the brain appeared to be correlated with extinction
retention.
Combining the results of the personality tests with the previously
reported data revealed that both improved extinction retention and
a thicker mOFC were associated with higher levels of extraversion
and lower neuroticism. Using a statistical tool that analyzes whether
one specific factor influences the relationship between the two
other factors, the researchers found that while the relation between
mOFC thickness and increased extraversion is mediated by extinction
retention, the association between mOFC thickness and extinction
retention does not seem to directly affect neuroticism.
"This study illustrates how measurement of a brain structure
can be linked to a complex character trait like extraversion through
a simpler behavioral measure like extinction retention," says
Scott Rauch, MD, director of the Psychiatric Neuroscience Research
Division in MGH Psychiatry and co-lead author of the paper. "Understanding
how personality is based in the brain is important both for insights
into personality disorders and for conditions in which personality
may confer vulnerability, such as anxiety disorders."
Rauch adds, "We are in the process of studying the link between
extinction retention and regional brain function and hope to investigate
how developmental factors may govern the structure and function
of the mOFC. The ability to modify mOFC activity may eventually
prove to be of therapeutic value." Rauch is an associate professor
of Psychiatry at Harvard Medical School.
The report's co-authors are Roger Pitman, MD, of MGH Psychiatry;
Brian Quinn and Bruce Fischl, PhD, of MGH Radiology; and Scott Orr,
PhD, of the VA Medical Center in Manchester, N.H. The study was
supported by grants from the National Institute of Mental Health,
the MGH Tosteson Fellowship, National Center for Research Resources,
National Institute of Biomedical Imaging and Bioengineering, and
the Mental Illness and Neuroscience Discovery Institute.
Massachusetts General Hospital, established in 1811, is the original
and largest teaching hospital of Harvard Medical School. The MGH
conducts the largest hospital-based research program in the United
States, with an annual research budget of nearly $500 million and
major research centers in AIDS, cardiovascular research, cancer,
cutaneous biology, medical imaging, neurodegenerative disorders,
transplantation biology and photomedicine. In 1994, MGH and Brigham
and Women's Hospital joined to form Partners HealthCare System,
an integrated health care delivery system comprising the two academic
medical centers, specialty and community hospitals, a network of
physician groups, and nonacute and home health services.
Media Contact: Sue
McGreevey, MGH Public Affairs
Physician Referral Service: 1-800-388-4644
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