No amygdalae = no fear

SM is a woman without fear. She doesn’t feel it. She has been held at knifepoint without a tinge of panic. She’ll happily handle live snakes and spiders, even though she claims not to like them. She can sit through reels of upsetting footage without a single start. And all because a pair of almond-shaped structures in her brain – amygdalae – have been destroyed.

Ralph Adolphs, Antonio Damasio and Daniel Tranel at the University of Iowa have been working with SM for over a decade. She is a 44-year old mother-of-three, who suffers from a rare genetic condition called Urbach-Wiethe disease, which has caused parts of her brain to harden and waste away. This creeping damage has completely destroyed her amygdala, a part of the brain involved in processing emotion (white arrows in the diagram below). She’s one of the few people who shows such a striking pattern of damage...

She lives in a poor area “replete with crime, drugs and danger”. As Feinstein writes, “she has been held up at knife point and at gun point, she was once physically accosted by a woman twice her size, she was nearly killed in an act of domestic violence, and on more than one occasion she has been explicitly threatened with death.” But in most of these situations, she didn’t act with urgency or desperation, something that police reports have corroborated.

It’s not that she doesn’t understand the concept of fear; after all, she knew that other people might be scared by the films she saw. However, she has a lot of problems with detecting danger. In a previous study, the team showed that she has no personal bubble. She’ll happily stand a foot away from complete strangers, far closer than most people would be comfortable with (even though, again, she understands the concept of personal space). It’s no surprise that she gets herself into a lot of difficult situations...

Even SM’s case doesn’t imply that the amygdala is the brain’s fear centre. Feinstein thinks that it’s more of a “broker”, going between parts of the brain that sense things in the environment, and those in the brainstem that initiate fearful actions. Damage to the amygdala breaks the chain between seeing something scary and acting on it...

“[SM]’s behaviour, time and time again, leads her back to the very situations she should be avoiding, highlighting the indispensable role that the amygdala plays in promoting survival by compelling the organism away from danger. Indeed, it appears that without the amygdala, the evolutionary value of fear is lost.”

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