Current Biology recently published a study on a woman who, due to brain damage to her amygdala, is unable to feel fear.
SM is a 44 year old woman with a rare genetic brain disorder, but that's not exactly why she's the object of medical scrutiny: The disease wiped out her amygdala, the part of the brain thought to handle fear. As a result, SM (her name has been withheld, as is common in medical studies) is apparently totally fearless. She's been the subject of medical study for over 20 years, and Current Biology just published one such study, conducted by University of Iowa researcher Justin Feinstein and his colleagues.
Earlier studies have shown SM has difficulty recognizing fear in the faces of others. She also participated in a study where she was repeatedly shown an blue square and blasted with a loud horn at the same time. Regular, fear-feeling individuals, upon seeing the square, would likely associate it with the sound, and startle or express fear; SM never did.
As part of the University of Iowa study, SM was shown scary movies, to no effect. She handled snakes in a pet store with ease, and asked to hold larger, more dangerous snakes, and to pet a tarantula. Researchers took her to a haunted house, and not once did she feel scared. The study seems to indicate the amygdala does, indeed, function as the fear center of the human brain.
A total lack of fear may sound more appealing than it actually is. Much like people who cannot feel pain can easily hurt themselves, SM doesn't experience fear to tell her situations may be unsafe. The AP reports, "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...She apparently hasn't felt fear as an adult, not even 15 years ago in an incident described by the researchers. A man jumped up from a park bench, pressed a knife to her throat and hissed, 'I'm going to cut you.'" SM's lack of fear is actually what got her into this predicament in the first place, though; she approached this individual when he called her over, even though she was alone, it was nighttime, and she said he appeared "drugged out."