Not being afraid of anything is the main symptom of a rare disease called Urbach-Wiethe's disease. Individuals with this disease are strangely not afraid of anything because the part of their brain that commands the sensation of fear and danger is "disconnected".
Scientists have sought answers to this disease because they may be able to explain and create effective treatment for individuals suffering from post-traumatic stress, such as soldiers returning from the war and not even leaving home, of so much fear.
The hope is that with the answers found they get a drug that will "turn off" that part of the soldiers' brains a little, as well as "reconnect" those with the Urbach-Wiethe disease.
Fear is a sensation that protects us and prevents us from avoiding dangerous situations that can take our lives. As in these individuals this part is found flawed, they become very curious people and can suffer from various problems like taking a snake bite or burning themselves during a fire.