For most of her life, SM, a 44-year-old mother of three, has been completely fearless. She has casually picked up large snakes that terrified her children, tried to touch tarantulas despite being warned about their painful bites, and when a mugger put a knife to her throat, she reacted with such eerie coolness that the man simply let her go. SM has Urbach-Wiethe disease, a disorder that only affects a few hundred people worldwide. It progressively destroys the amygdala, the almond-shaped part of the brain that is the anatomical seat of fear. While SM did feel some fear during her childhood before the disease progressed, after age 10 she could no longer experience fear. Even so, her IQ is normal, her memory is good, and her language and perception skills are on point. The only problem she has is dealing with fear. Researchers at the University of Iowa have been working with SM for over a decade. Back in 1994, researchers showed that SM even has trouble recognizing fear in other people. She can’t tell what fearful facial expressions mean, even though she’s more than capable of discerning other emotions. In a 2010 study, the team discovered that SM can't detect danger. In the end, researchers came to the conclusion that damage to the amygdala breaks the chain between seeing something scary and acting on it. SM’s behavior, time and time again, will lead her back to the very situations she should be avoiding.
