What would you do if you weren't afraid of anything?

She's not afraid of snakes or spiders. Haunted houses and makes-your-blood-run-cold horror flicks have no effect. Franklin Delano Roosevelt once said "the only thing we have to fear is fear itself," but she's not afraid of fear, either. A rare genetic disease has wiped out her amygdala-the fear center of her brain-and nothing, not even being held up at knife-point, scares her anymore.

University of Iowa researcher Justin Feinstein and his team studied the 44-year-old mother of three, whom they refer to simply as "SM" in a study published this week in the journal Current Biology.

"To provoke fear in SM, we exposed her to live snakes and spiders, took her on a tour of a haunted house, and showed her emotionally evocative films. On no occasion did SM exhibit fear, and she never endorsed feeling more than minimal levels of fear," the researchers wrote. They also asked her to rate her sense of fear in questionnaires and evaluated traumatic incidents in her past, and still, "SM repeatedly demonstrated an absence of overt fear manifestations and an overall impoverished experience of fear."

It sounds fabulous and liberating, but not feeling fear can put a person in some pretty dangerous situations-and the researchers say that SM has put herself in harm's way many times.

Fifteen years ago, for example, while walking through a park alone late at night, a man jumped from a park bench and held a knife to her throat, threatening to cut her. Feinstein said that a church choir was practicing in the distance, and SM responded by telling her attacker, "If you're going to kill me, you're going to have to go through my God's angels first." The man let her go, but she didn't run home-she walked.

"Her lack of fear may have freaked the guy out," Feinstein told the Associated Press.

Yet, even though she doesn't seem to feel fear now, she did when she was a child, researchers said, which may mean that the disease didn't destroy her amygdala until she was older. SM does seem to experience a wide range of other emotions, including excitement. And she understands that certain situations are frightening (she told researchers she hates snakes and spiders), she's just doesn't feel fear when she experiences them.

This study seems to confirm the role that the amygdala plays in fear and may lead to the discovery of treatment options for Post Traumatic Stress Disorder. A different study earlier this year, using mice, showed that it may be possible to erase our worst memories by using a drug to eliminate proteins that are created in the brain when we experience a traumatic event.

"This past year, I've been treating veterans returning home from Iraq and Afghanistan who suffer from PTSD. Their lives are marred by fear, and they are oftentimes unable to even leave their home due to the ever-present feeling of danger," Feinstein said in a press release. "In striking contrast, the patient in this study is immune to these states of fear and shows no symptoms of post-traumatic stress. The horrors of life are unable to penetrate her emotional core. In essence, traumatic events leave no emotional imprint on her brain."

We're fascinated. What would you do if you weren't afraid of anything?

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