A woman with bilateral damage relatively restricted to the amygdala is the subject of a case study recently reported.
SM, as she will be known to the public, seems able to experience emotions such as happiness and sadness normally, but shows no signs of fear.
This article offers more details about the remarkable SM and gives a glimpse into possible directions for the research to take such as non-invasively controlling the amygdala to reduce fear in PTSD sufferers.
When the brain knows no fear
A new study, published online on December 16 in Current Biology, a Cell Press publication, offers new insight into the emotional life of a unique individual who completely lacks the function of an almond-shaped structure in the brain known as the amygdala. Studies over the last 50 years have shown that the amygdala plays a central role in generating fear reactions in animals from rats to monkeys. Based on the detailed case study of the woman identified only as SM, it now appears that the same is true of humans.The finding offers a powerful take on the connection between the brain and behavior, specifically in the context of situations that would normally evoke fear, the researchers say.
“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 of 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.”
Feinstein says that the average person may have different definitions of fear, but his goal ultimately is to define emotions including fear based on the biological machinery that triggers them.
“Normally, the amygdala is constantly sorting through all the information coming into our brain through the different senses in order to rapidly detect anything that might impact our survival,” he explained. “Once it detects danger, the amygdala orchestrates a rapid full-body response that compels us to stay away from the threat, thereby improving our chances for survival.”
To explore this role of the amygdala, Feinstein and his Univeristy of Iowa 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 over a 3-month period. Across all questionnaires, measures, and scenarios, SM failed to experience fear.
That apparent lack of fear mirrored her personal experience, 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. Yet, she is able to feel other emotions such as happiness and sadness. Taken together, these findings suggest that the human amygdala is a pivotal area of the brain for triggering a state of fear.”
Feinstein said he was most surprised at what happened when SM was presented with snakes and spiders in an exotic pet store. “For many years, SM has been telling us that she ‘hates’ snakes and spiders and ‘tries to avoid them.’ Going into the experiment, everyone, including myself, thought SM would stay away from these animals. Yet, to our surprise, she immediately started touching them! When asked why she was touching something that she claims to hate, she appeared perplexed by her own behavior and stated that she was overcome with curiosity. It was as if the part of the brain responsible for SM’s cognition and thoughts was completely disconnected from the part of the brain controlling her behavior.”
Feinstein says the new findings suggest that methods designed to safely and non-invasively turn off the amygdala might hold promise for those suffering from post-traumatic stress disorder (PTSD).
“This past year, I’ve been treating veterans returning home from Iraq and Afghanistan who suffer from PTSD,” he said. “Their lives are marred by fear, and they are oftentimes unable to even leave their home due to the ever-present feeling of danger. In striking contrast, SM is immune to these states of fear and shows no symptoms of post-traumatic stress. In essence, traumatic events leave no emotional imprint on SM’s brain. By understanding how the brain processes fear through cases like SM, we may one day be able to create treatments that selectively target the brain areas that allow fear to take over our lives.”
Contact: Elisabeth (Lisa) Lyons – Cell Press
Source: Cell Press
SM shows no fear due to missing amygdala it is believed. Images by Life Science Databases(LSDB) via Wikimedia Commons.
"SM" is a bit of an emotional anomaly. The 44-year-old mother, given those initials to preserve her anonymity, isn't scared of snakes. She doesn't shriek when she sees a scary movie. Even haunted houses don't give her chills. SM is pretty much fearless—and now scientists think they've figured out why.
The study's lead authors met SM, who has a rare genetic condition called Urbach-Wiethe disease, more than 2 decades ago. As a result of her illness, she has "two perfectly symmetrical black holes" where her amygdala should be, says Justin Feinstein, a graduate student in clinical psychology at the University of Iowa in Iowa City. The amygdala is a pair of almond-shaped clusters of neurons in the brain that play a role in fear and anxiety. And indeed, when the researchers examined SM, they found that she could not recognize fear on others' faces.
In the new study, the researchers—who now included Feinstein—tested whether SM could experience fear. They took her to a pet store filled with snakes and spiders, showed her clips from horror films (including The Silence of the Lambs and The Shining), and brought her to the annual haunted house at the Waverly Hills Sanatorium in Louisville, Kentucky, a notoriously scary place.
In each situation, SM failed to act fearful. Instead, she seemed excited and curious. In the pet store, for example, she held a snake and rubbed its scales despite telling the researchers that she "hates" snakes. In the haunted house, SM led the way, smiling and laughing. SM didn't report feeling scared. Throughout each experience, the researchers asked her to rate her fear on a scale of 1 to 10. In each case, she selected low values, 2 or lower. But SM isn't an unfeeling robot. She reports experiencing other emotions—surprise, happiness, disgust—and understands that scary movies might induce fear in others.
The researchers also gave SM an electronic diary. Three times each day, the diary displayed a list of 50 questions asking her to rate her current emotional state. The emotion that received the highest average rating during the 3 months SM had the diary was "fearless." She never reported being scared, fearful, or afraid. Similarly, SM's score was much lower than normal on a series of questionnaires aimed at assessing recent fear and how much fear she would feel in a series of hypothetical situations, such as talking to other people or getting lost.
When the researchers delved into SM's past, they found the same fearlessness. The woman says she is scared of snakes, but her son once saw her pick up a large snake and move it off the road. When SM was held at knifepoint in a dark park, she recalls remaining calm and not being scared. As an adult, SM has been the victim of numerous crimes, but the only fearful experiences she could recall happened when she was a child. The researchers posit that the bulk of the damage to SM's amygdala occurred at about the age of 10.
The results suggest that "the amygdala is a critical brain region for triggering a state of fear when an individual encounters threatening stimuli," Feinstein and his co-authors write today in Current Biology. It's the first human study to show that amygdala damage can wipe out fearful feeling, they say. It also contradicts a 2002 paper that showed that patients with damage to one or both halves of the amygdala had no deficit in their ability to feel fear.
The authors point out that the amygdala communicates with other regions of the brain to orchestrate the fear response. "Because SM is missing her amygdala, she doesn't have this cascade of responses that comprise a state of fear," Feinstein says. "And because of that, she's unable to feel fear."
"It's an important observation," says David Anderson, a neurobiologist at the California Institute of Technology in Pasadena who studies the neural circuits involved in fear. But he notes that there's no way to unequivocally prove that SM's responses are the result of damage to her amygdala. "One would like to have more subjects than just one," he says.
Elizabeth Phelps would also like to see evidence in more patients. "I don't believe you can make a general statement about what the amygdala does by a single case study," says the cognitive neuroscientist at New York University and author of the 2002 study that returned opposite results. The authors, she says, were too bold in their conclusions. "The data are mixed."
If confirmed, Feinstein says the findings might lead to new therapies for post-traumatic stress disorder, such as new forms of psychotherapy that hinder the amygdala's activity. Still, fear is an important emotion, notes Anderson. So "you would not want to advocate permanent destruction of the amygdala in soldiers as a way to protect against possible post-traumatic stress disorder," Anderson says.
As for Feinstein's own amygdala, it appears to be intact. "A lot of things scare me, including snakes and spiders," he says. "You couldn't pay me enough money in the world to touch these animals."