Fear - What Happens If You Can’t Feel It?

What if there were no fear at all in your emotions? If threats could not raise your internal alarm system anymore, what happens then? Would your life be bolder or just more dangerous? Very few people live just that way, victims of an extremely rare neurological condition that disables the brain's fear circuit. 

This condition is appropriately referred to as Urbach-Wiethe disease, a genetic condition that has only had roughly 400 cases documented globally. The condition results in amygdala degeneration as well as amygdala calcification that is heavily involved in the response of fear. 

One of the best-documented case histories is that of S.M., a woman who, due to Urbach-Wiethe disease, has experienced bilateral destruction of the amygdala and therefore an extremely impaired capacity for experiencing fear when confronted with an external threat. She will exhibit no fear when confronted by snakes, spiders, haunted houses, horror films, or any of those stimuli that would reliably make other individuals feel alarm. 

However, high levels of carbon dioxide (CO₂). That means that certain internal physiological causes of fear may short-circuit the amygdala and invoke different brain pathways. 

The amygdala is certainly pivotal but not the complete picture. S.M.'s case of nearly complete lack of fear of external threats puts the focus on the amygdala's key input of distinguishing danger from the environment and requesting the correct response - raised heart rate, increased arousal, and avoidance behaviour. Truly, there have been repeated findings of amygdala activation with exposure to fearsome faces or threatening situations in healthy individuals. 

Nevertheless, S.M.'s panicking response upon exposure to CO₂ refutes such an interpretation: it suggests that fears that are secondary consequences of internal physiological imbalances, such as signals of suffocation, could have extramygdalar sites of origin. That is, fear is not a single process but rather an integrated multiple system of interconnected processes. 

Scientists have advanced a dichotomy: external fear, which results from threats from the external world, heavily relies on the processing carried out by the amygdala. In comparison, internal fear or panic that results from body signals (e.g., shortness of breath) could be mediated by related brain centers such as the brainstem, insula, or diencephaloncan develop panic attacks otherwise. 

Additionally, experiments have verified that patients and healthy individuals do indeed process fear and panic differently. In one such study, patients with damaged amygdala were the first to yield to panic while breathing in CO₂, sometimes even more than control subjects 

Far from being a consistent structure, the amygdala consists of different subnuclei like the basolateral amygdala (BLA), which serve separate roles in the emotion of fear regulation. In fact, certain experiments suggest that if the BLA gets damaged, there will be a higher sensitivity toward fearful faces, meaning that the BLA is responsible for an inhibition of the innate fear response. 

Existing without fear is not only emotionally foreign but also dangerous. Since fear serves to prevent harm (e.g. fire, heights, predators), lacking fear implies individuals will expose themselves to harm innocently. S.M. has shared life experiences of not experiencing a normal fear response but living by circumstance or external forces. 

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