A 44-year-old woman with a rare form of brain damage can literally feel no fear, according to a case study published yesterday in the journal Current Biology. Referred to as SM, she suffers from a genetic condition called Urbach-Wiethe Disease. The condition is extremely rare, with fewer than 300 reported cases since it was first described in 1929, and is caused by a mutation in a gene on chromosome 1, which encodes an extracellular matrix protein. The symptoms vary widely, and in about 50% of cases there is calcification, or hardening, of structures in the medial temporal lobe of the brain. In SM’s case, it led to degeneration of the amygdala (below), a small, almond-shaped structure known to be involved in fear and other emotions.
SM has been studied extensively during the past two decades. Early investigations showed that her non-verbal visual memory was signficantly impaired but that otherwise she had an IQ in the low-average range. She also displayed inappropriate social behaviours, quickly becoming friendly with the experimenters and making sexual remarks, due to disturbed executive control. Subsequently, it was found that she was unable to recognize emotions in facial expressions, and a study published earlier this year showed that the brain damage had eliminated her monetary loss aversion - that is, she makes risky financial decisions that most of us would avoid because of a fear of losing money.
None of these previous studies assessed her experience of fear, however. Justin Feinstein of the University of Iowa and his colleagues therefore tested SM’s fear responses, using a very simple method - by trying to scare her. First, they took her to an exotic pet store and exposed her to snakes and spiders, which, she had told them, she “hated” and “tried to avoid”. Nevertheless, she seemed fascinated by the large collection of snakes, and was compelled to touch and poke the larger and more dangerous ones, as well as a tarantula, but had to be stopped in case she got bitten. Throughout the visit, she was asked to rate her fear on a scale of 0 to 10, and her ratings were never greater than 2.
Next, the researchers took SM on a Halloween visit to Waverly Hills Sanatorium in Louisville, Kentucky, which features people dressed as monsters, murderers and ghosts and is reported to be “one of the most haunted places in the world”. When they arrived, she voluntarily led the researchers and a goup of five strange women around the house, walking into dark corners and hallways without hesitation. The hidden monsters tried to scare her numerous times, unsuccessfully. Whereas the five other women in the group screamed loudly whenever they encountered one, SM laughed and smiled at them, and even scared one by poking it in the head because she was curious about how it felt. She rated her fear level at 0 throughout, saying instead that she found it exciting.