SM, a 44-year old mother of three, experienced absolutely no fear through her adulthood until recently.
The reason for her lack of fear was the genetic degenerative disease known as Urbach-Wiethe, named after its finders. The disease causes the progressive destruction of the amygdalae, two bean-shaped structures in the brain responsible for triggering fear and aggression.
Due to it being progressive, SM still had childhood fears for things like snakes and tarantulas, but released the fears when the amygdalae were slowly being destroyed.
In one instance where a mugger threatened her at knife point, she was so eerily calm, she scared the attacker away.
Not only does she not process fear, but she is unable to recognize fear in others. She cannot seem to draw a scared face because she does not know what that kind of face looks like.
When watching clips from movies, she laughed at the right places, screamed in disgust at the right places, and yet had no reaction to the scary movies she viewed ("The Ring", "The Shining", & "Seven").
This lack of fear comes hand in hand with her inability to detect danger. While you and I would stand distantly from a suspicious character, SM would be able to stand within inches of distance from them.
However, a recent study showed that fear might still occur in patients with Urbach-Wiethe. The fear was instigated by being placed in a room that held a concentrated carbon-dioxide making SM feel a sort of "air hunger" caused by the lack of oxygen.
This shows that while they may be unable to show fear for external factors like spiders or snakes, their body can still sense danger that occurs within itself.
Would you rather live a fearless life? Or would you prefer to keep those pesky fears in the hopes that it will save you from danger one of these days?