Fear is often felt before we fully register a threat, surfacing as an instinctive rush that sharpens the senses and urges the body to react. It can appear in ordinary moments, such as hesitating on a dark street, or in more extreme situations that demand immediate action. Although fear is a universal experience, its biological roots remain complex, involving intricate interactions between sensory input, memory, and emotional interpretation. Much of this process unfolds deep within the brain, in a structure known as the amygdala. Research has long pointed to the amygdala as central to recognising danger and coordinating the physical and emotional reactions that follow, yet rare neurological cases provide the clearest insight into what happens when this mechanism is disrupted.
The woman who cannot feel fear: The case of S.M.
Among the most revealing cases is that of a woman with a confidential identity referred to as S.M., whose life has become a cornerstone of modern fear research. S.M. is notable not for extreme fear, but for the near absence of it. A study published in Current Biology recorded that her behaviour in situations that reliably provoke fear in most people is strikingly different. She has walked through dangerous neighbourhoods at night without hesitation, touched venomous snakes with curiosity rather than caution, and navigated haunted attractions with an ease that puzzled researchers observing her responses. She shows no signs of anxiety, avoidance, or discomfort in circumstances that usually trigger an instinctive alarm. This unusual pattern makes her an invaluable subject in understanding how the brain constructs the experience of fear and how behaviour changes when that experience is missing.
What is the rare condition and what causes it
S.M.’s lack of fear is the result of Urbach Wiethe disease, an extremely rare genetic condition that causes selective damage to the amygdala through calcification. While the disorder can affect skin and mucous membranes, in S.M.’s case it produced near complete bilateral destruction of the amygdala, leaving most other brain structures intact. This unique pattern of damage allows researchers to examine amygdala function without the confounding effects of broader neurological impairment. The rarity of the condition adds to its scientific value. Few documented cases show such targeted damage, and even fewer maintain stable cognitive function, which makes S.M.’s neurological profile a rare window into the neural circuitry that shapes emotional life. Her case demonstrates that the amygdala is not simply involved in fear but is essential for generating the coordinated physiological and subjective components that define the emotion.
A day in the life of a person who doesn’t feel fear
The absence of fear has affected nearly every part of S.M.’s day-to-day experience. Without the natural restraints that fear typically imposes, she often moves through the world with a sense of openness that borders on vulnerability. Situations that would prompt most people to pause or withdraw are approached by her with interest, and occasionally with enthusiasm. This has placed her in risky circumstances, including encounters with potentially dangerous individuals and unsafe environments. Socially, she struggles to recognise fear in the expressions and voices of others, which can disrupt her ability to interpret emotional cues and gauge interpersonal dynamics. Her behaviour highlights the extent to which fear supports everyday decision-making, encourages protective choices, and shapes social understanding. Cognitive awareness of danger is not enough on its own; without the emotional force provided by the amygdala, decisions lack the urgency that fear usually supplies.
How scientists measured fear in patients who cannot feel it
To explore these mechanisms more systematically, researchers conducted extensive experiments with S.M. and two other individuals who also had bilateral amygdala damage. The results, described in a study published in Nature Neuroscience, revealed consistent patterns across participants. When exposed to spiders, snakes, haunted environments, and emotionally charged film clips, the patients showed minimal physiological arousal and reported almost no subjective fear. Their reactions contrasted sharply with those of typical participants, who displayed clear signs of heightened autonomic activity. Even during tasks designed to trigger panic, such as inhaling concentrated carbon dioxide, the patients showed an altered pattern of response, indicating that while certain panic reactions may bypass the amygdala, the feeling of fear itself depends heavily on its activity. These findings show that the amygdala is not only important for detecting threats but also crucial for linking bodily reactions with the emotional sensation of fear.
Why this rare case reshaped fear research
The insights gained from these patients extend far beyond individual neurological curiosity. They clarify how the amygdala integrates perception, memory, and physiological change into the cohesive state we recognise as fear. This has implications for understanding anxiety disorders, post-traumatic stress disorder, phobias, and other conditions in which fear responses are heightened, disrupted, or poorly regulated. By studying what happens when fear is absent, researchers can better understand what occurs when fear is excessive or intrusive. These cases also challenge long-held assumptions about how emotion is organised in the brain, revealing that even subtle structural changes can fundamentally alter the way a person navigates the world. The study of S.M. and similar patients continues to shape scientific perspectives on emotion, emphasising the delicate balance between neural function and human experience.Also Read | Why public toilets trigger anxiety for so many: The hidden mental health issue linked
