Mo at Neurophilosophy:
The patient known as S.M. has not experienced fear since she was a child, and has fascinated brain researchers for many years. In 2010, one team noted that she makes risky financial decisions in experimental economics games, because she isn't afraid of losing money. Another tried everything they could to frighten the life out of her – but failed. They showed her clips from some of the scariest horror films ever made, asked her to handle large spiders and snakes, and took her to a haunted house. On no occasion did she show the smallest sign of fear, even when faced with traumatic events and potentially life-threatening threats.
Now in her mid-40s, S.M. is one of fewer than 300 people to be diagnosed with Urbach-Wiethe disease, a genetic condition that causes a brain structure called the amygdala to gradually harden up and shrivel away.
Researchers recently found something that causes intense fear in people with this condition.