"A middle-aged woman known as SM blithely reaches for poisonous snakes..." (Image by JamieS93.)

A rare genetic disorder called Urbach-Wiethe disease obliterates the capacity for the amygdala portion of the brain to cause a person to feel fear. Someone with this congenital condition never becomes afraid, even when it’s the best thing for their well-being. (Thanks Reddit.) An excerpt about the condition from Laura Sanders’ Science News article:

“A middle-aged woman known as SM blithely reaches for poisonous snakes, giggles in haunted houses and once, upon escaping the clutches of a knife-wielding man, didn’t run but calmly walked away. A rare kind of brain damage precludes her from experiencing fear of any sort, finds a study published online December 16 inCurrent Biology.

SM has an unusual genetic disorder called Urbach-Wiethe disease. In late childhood, this disease destroyed both sides of her amygdala, which is composed of two structures the shape and size of almonds, one on each side of the brain. Because of this brain damage, the woman knows no fear, the researchers found.

Experiments have strongly implicated the amygdala in fear processing. Many of these were conducted on animals with amygdala damage. ‘But one thing we’ve never known for sure, because they’re animals, is whether they can consciously feel fear,’ says study coauthor Justin Feinstein of the University of Iowa in Iowa City. ‘So we said, Let’s take a human patient who has this same sort of damage, and for the first time, actually figure out how they’re feeling.’

Feinstein and his colleagues sifted through SM’s past, looking for instances when she should have been scared. SM said she never felt fear, even when threatened with a knife or a gun. The researchers gave SM an electronic diary that she carried for three months to record her emotional state. Fear didn’t make an appearance in the list of emotions. On a battery of questionnaires, SM wrote that she wasn’t afraid of public speaking, death, her heart beating too fast or being judged negatively in a social setting.”