A woman who cannot feel fear due to a rare medical condition continues to baffle medical experts 30 years after doctors began studying her, NPR revealed in a recent episode of "Invisibilia."
The woman, only identified as SM, is a 40 something-year-old U.S. resident with three children. Her life is normal in every aspect expect for the fact that she is biologically unable to feel fear, the result of a condition known as Urbach-Wiethe disease. It causes pieces of the brain to harden and waste away, including the part responsible for triggering fear responses in the body.
There have only been 400 confirmed cases of the disease in the world, NPR reported.
In order to protect SM from public scrutiny- and potential danger from anyone wanting to test her condition- scientists have carefully guarded her identity. She was never before interviewed until Dr. Daniel Tranel, a neuroscientist who's studied SM for 20 years, spoke with her and gave the conversation to NPR.
When Tranel asked SM what fear is, she said, "Well, that's what I'm trying to- to be honest, I truly have no clue."
"I wonder what it's like, you know, to actually be afraid of something," said SM, who was once held at gunpoint but still felt nothing.
With Urbach-Wiethe disease, calcium deposits form in parts of the brain and harden over time. In SM's case, the affected part of her brain is the amygdala, which is responsible for processing fear, doctors told NPR. In a normal person the amygdala would trigger a person's heart to race or cause them to sweat. That's not the case with SM.
"It's a little bit as if you would go to this region and literally scoop it out," Antonio Damasio, a neuroscientist at the University of Southern California, told NPR.
Doctors have noticed the disorder, which can cause a hoarse voice or bumps around the eyes, makes SM an unusually friendly and open person. But its also gotten her into situations where she almost died for lack of fear.
A man once held a knife to her throat and threatened to cut her.
"I told him- I said, go ahead cut me. And I said, I'll be coming back, and I'll hunt your ass," SM told Tranel. She did not call the cops after the incident.
Another time she was held at gunpoint- twice. She was also almost beaten to death by her first husband, NPR reported. Still, she never got scared.
Doctors say traumatic experiences will never affect SM because her brain doesn't process bad things that happen to her as bad. Researchers hope her condition can shed light on treating Post-Traumatic Stress Disorder, Live Science reported, which may hold promise because SM said she is generally a happy person.
"You know, there's some days I could be on top of the world," said SM, whose disease is not expected to shorten her life, "and there's some days that, you know, I can be- got the blues. But 9 out of 10, I'd say happy."
