NEW YORK – Meet SM, a 44-year-old woman who literally knows no fear.
She's not afraid to handle snakes. She's not afraid of the "The Blair Witch Project," "The Shining," or "Arachnophobia." When she visited a haunted house, it was a monster who was afraid of her.
SM isn't some cold-blooded psychopath or a hero with a tight rein on her emotions. She's an ordinary mother of three with a specific psychological impairment, the result of a very rare genetic disease that damaged a brain structure called the amygdala (uh-MIG'-duh-luh).
Her case shows that the amygdala plays a key role in making people feel afraid in threatening situations, researchers say.
Her life history also shows that living without fear can be dangerous, they said.
A study of her fearlessness was published online Thursday in the journal Current Biology by University of Iowa researcher Justin Feinstein and colleagues. As is typical, the paper identifies her only as "SM." Feinstein declined to make SM available for an interview with The Associated Press, citing laboratory policy about confidentiality.
An expert unconnected with the study cautioned against drawing conclusions about the amygdala, noting that her own work with a similarly brain-damaged woman found no such impairment. But another expert said the new finding made sense.
SM has been studied for more than 20 years, and many papers have been published about her fear-related abnormalities. She has trouble recognizing fear in facial expressions, for example.
In another experiment, published in 1995, she was blasted with a loud horn every time she saw a blue-colored square appear on a screen. Despite the repeated blasting horn, she never developed the fear an ordinary person would feel when seeing the blue square.
Other research shows SM scores normally on tests of intelligence, memory and language, and she experiences emotions other than fear. She lives independently.
SM recalls being afraid as a child, like the time she was cornered by a snarling Doberman pinscher. But maybe that was before her disease wiped out the amygdala in both the left and right sides of her brain, the researchers say.