"SM" has a rare brain condition that's wiped out her amygdala—thought to be the brain's fear center. Researchers put her in a bunch of frightening situations but didn't scare her once. Sounds like the most fun study ever.
Being unable to experience fear sounds, awesome right? You can just bungee jump all day and stick your head into lions' mouths at night. But, actually it's pretty dangerous. Here's a characteristic incident in the life of SM, who suffers from a rare brain condition called lipoid proteinosis which has left holes where her amygdala should be. From the AP:
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, who heard a church choir practicing in the distance, looked coolly at him and replied, "If you're going to kill me, you're going to have to go through my God's angels first."
The man suddenly let her go. She didn't run home. She walked.
This would be fine, if her fearlessness hadn't gotten her into the situation in the first place: She walked right up to the guy when he called out to her even though it was late at night and he looked "drugged out," according to the AP.
Researchers wanted to make sure SM was actually fearless and not just a really good liar. So, they ran her through a series of increasingly intense horrors: They brought her to a pet store and had her hold enormous snakes (she loved it and even had had to be stopped from petting a tarantula); they showed her scary movies and took her to a haunted house. Finally, they told her that George Lucas was going to make another three Star Wars prequels. (Kidding!) Never once did she show fear or report feeling scared, apparently confirming the role of the amygdala in human fear.
Their results are published in the latest issue of Current Biology, which you can purchase in a trough full of maggots at the end of a very scary roller coaster. Boo!