Known simply as SM, the woman from Iowa in America, suffers from a condition called Urbach-Wiethe disease which has destroyed a part of her brain known as the amygdala.

This almond shaped structure in the centre of the brain has long been associated with emotional learning, and experiments on animals have shown that removing it makes them fearless.

But this is the first time scientists have been able to prove it in humans and now they hope it will help them develop treatments for extreme anxiety conditions such as post traumatic stress disorder.

What is interesting about SM is that she has experienced fear as a child and knows that she should be afraid, yet due to her condition, as an adult she is never scared.

“The nature of fear is survival and the amygdala helps us stay alive by avoiding situations, people, or objects that put our life in danger,” said Justin Feinstein the lead researcher at the University of Iowa.

“Because SM is missing her amygdala, she is also missing the ability to detect and avoid danger in the world. It is quite remarkable that she is still alive.”

To explore this role of the amygdala, Mr Feinstein and his team observed and recorded SM’s responses in a variety of situations that would make most people feel fear. They exposed her to snakes and spiders, took her to one of the world’s scariest haunted houses, and had her watch a series of horror films.They also had her fill out questionnaires probing different aspects of fear, from the fear of death to the fear of public speaking. On top of that, SM faithfully recorded her emotions at various times throughout the day while carrying around an electronic diary. Across all questionnaires, measures, and scenarios, SM failed to experience fear.

Mr Feinstein said. “In everyday life, SM has encountered numerous traumatic events which have threatened her very existence, and by her report, have caused no fear. She was held up at gunpoint and at knifepoint and was almost killed during a domestic incident.”

S.M. told researchers she did not feel fear during these life-threatening situations.

Yet, she is able to feel other emotions such as happiness and sadness. 

 “The horrors of life are unable to penetrate her emotional core. In essence, traumatic events leave no emotional imprint on her brain.” 

(research published in the journal ”Current Biology.”)