A study published in the journal Current Biology examined how certain parts of the brain respond to fear. The study, published in December, specifically investigated one woman, known as S.M., because she is one of very few people known to have damage to the amygdala on both sides of her brain. The amygdala is a portion of the brain thought to play a role in processing fear and other emotions.
S.M. suffers from a rare condition, Urbach-Wiethe disease, which caused calcium deposits to form and cause lesions on the amygdala. The researchers exposed S.M. to fear-inducing stimuli and used questionnaires to assess whether she experienced the symptoms of fear over a three-year period. They also asked her to rate the level of different emotions at random times for a three-month period. S.M. reported little-to-no symptoms of fear on the questionnaires and also rated herself as fearless most often during the emotional experience sampling. However, she did experience other emotions, such as joy, happiness and sadness normally, the researchers said.
S.M.’s lack of fear has created some risky situations for her. She was held at knifepoint in a park at one point. Her fearlessness may have contributed to that incident. She was in the park by herself when, what she described as, a “drugged out” man called her over to a bench. She went. While he held her at knifepoint, she calmly responded that if he was going to kill her, he would have to go through her angels. The man let her go. She walked, not ran, home. S.M. has also been held at gunpoint and was also almost killed in a domestic incident.
“It’s very striking that she has only a rational response, not a physiological one,” said Dr. Jon Shaw, professor of psychiatry at the University of Miami School of Medicine. “The body is not prepared for a physiological response because the amygdala has been taken out of the loop.”
Although it certainly appears that the amygdale is critical to fear response, some experts caution against drawing too many conclusions from one study. This study’s findings, however, may be very significant in treating Post-Traumatic Stress Disorder. “[This] puts us in a position to design treatments to target that structure to treat conditions marked by pathological fear reactions,” said Daniel Tranel, one of the study authors and professor of neurology and psychology at the University of Iowa. “Probably the most well-known such condition is PTSD.”
S.M.’s case also underscores that fear is essential to human’s survival. The researchers believe that because she could not detect threats to her safety and avoid them, she wound up in numerous life-threatening situations. “Indeed, it appears that without the amygdala, the evolutionary value of fear is lost,” the authors wrote.