THURSDAY, Dec. 16 (HealthDay News) -- Researchers who have
studied a woman with a missing amygdala -- the part of the brain
believed to generate fear -- report that their findings may help
improve treatment for post-traumatic stress disorder (PTSD) and
other anxiety disorders.
In perhaps the first human study confirming that the
almond-shaped structure is crucial for triggering fear, researchers
at the University of Iowa monitored a 44-year-old woman's response
to typically frightening stimuli such as snakes, spiders, horror
films and a haunted house, and asked about traumatic experiences in
The woman, identified as S.M., does not seem to fear a wide
range of stimuli that would normally frighten most people.
Scientists have been studying her for the past 20 years, and their
prior research had already determined that the woman cannot
recognize fear in others' facial expressions.
S.M. suffers from an extremely rare disease that destroyed her
amygdala. Future observations will determine if her condition
affects anxiety levels for everyday stressors such as finance or
health issues, said study author Justin Feinstein, a University of
Iowa doctoral student studying clinical neuropsychology.
"Certainly, when it comes to fear, she's missing it," Feinstein said. "She's so unique in her presentation."
Researchers said the study, reported in the Dec. 16 issue of the
Current Biology, could lead to new treatment strategies for
PTSD and anxiety disorders. According to the U.S. National
Institute of Mental Health, more than 7.7 million Americans are
affected by the condition, and a 2008 analysis predicted that
300,000 soldiers returning from combat in the Middle East would
"Because of her brain damage, [the patient] appears to be immune to PTSD," Feinstein said, noting that she is otherwise cognitively typical and experiences other emotions such as happiness and sadness.
In addition to recording her responses to spiders, snakes and
other scary stimuli, the researchers measured her experience of
fear using many standardized questionnaires that probed various
aspects of the emotion, such as fear of death or fear of public
speaking. She also carried a computerized emotion diary for three
months that randomly asked her to rate her fear level throughout
Perhaps most notable, Feinstein said, are her many near-misses
with peril because of her inability to avoid dangerous
circumstances. In one case, when she was 30, she approached a
drugged out-looking man late one night who pulled a knife and
threatened to kill her.
Because of her complete absence of fear, the woman -- who heard
a choir singing in a nearby church -- responded, "If you're going
to kill me, you're going to have to go through my God's angels
first." The man abruptly let her go.
The mother of three was also seen by her children approaching
and picking up a large snake near their home with no seeming regard
for its ability to harm her, Feinstein said.
"Its a perfect example of the sort of situation she gets herself in that anyone without brain damage would be able to avoid," Feinstein said. "With her brain damage, she's so trusting, so approachable to everything. In hindsight, [her response to the man with the knife] may have saved her life because the guy got freaked out."
Alicia Izquierdo, an assistant professor of psychology at
California State University in Los Angeles, said the study results
add to existing evidence that the amygdala should be targeted in
developing therapies for phobias, anxiety disorders and PTSD,
"where too much fear is a bad thing."
"In small doses, fear is a good thing -- it keeps us alive," Izquierdo said. "For many years, we have known from studies in rodents and monkeys that the amygdala is necessary for the normal expression of fear. Those who study the amygdala in animals are limited, however . . . and can only speculate about what this brain region does for the experience of fear."
"This is one reason why the study . . . is so meaningful: We can now say that the amygdala is important for the expression and the subjective experience of fear," she added.
Feinstein said PTSD treatment tactics targeting the amygdala
would not involve surgically removing or altering it. Rather, it is
thought that the amygdala's hyperactive response in frightening
situations can be modified over time through repetitively doing
things a patient considers scary.
"This prolonged exposure therapy involves approaching the things causing them distress and fear the most," Feinstein said. "We don't ever want to surgically alter this area."
For more on PTSD, go to the
U.S. National Institute of Mental Health.
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