Researchers at the University of Iowa have confirmed that a female patient with a damaged amygdala is utterly incapable of feeling fear.
To be sure, the patient was exposed to various "frightening" stimuli, including a haunted house, snakes, spiders and horror films.
Nevertheless, each of the above-mentioned stimuli failed to produce even the slightest feeling of fear.
Senior study author Dr. Daniel Tranel explained that tests conducted over the past 50 years show the amygdala playing a definite "central role" in generating fear reactions in animals from rats to monkeys.
However, this study confirms for the first time that the amygdala - an almond-shaped brain region - is also responsible for triggering a state of fear in humans.
According to Tranel, the discovery could lead to the development of new treatments for PTSD and related anxiety disorders.
"This finding points us to a specific brain area that might underlie PTSD. Psychotherapy and medications are the current treatment options for PTSD and could be refined and further developed with the aim of targeting the amygdala."
Justin Feinstein, lead study author and a UI doctoral student studying clinical neuropsychology, expressed similar sentiments.
"This past year, I've been treating veterans returning home from Iraq and Afghanistan who suffer from PTSD. 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, the patient in this study is immune to these states of fear and shows no symptoms of post-traumatic stress. The horrors of life are unable to penetrate her emotional core. In essence, traumatic events leave no emotional imprint on her brain."
Indeed, all "scary" scenarios - including numerous traumatic events that threatened the patient's very existence - have caused absolutely no fear.
"Taken together, these findings suggest that the human amygdala is a pivotal area of the brain for triggering a state of fear," said Feinstein.
"While the patient is able to experience other emotions, such as happiness and sadness, she is unable to feel fear. This suggests that the brain is organized in such a way that a specific brain region - the amygdala - is specialized for processing a specific emotion - fear."
However, perhaps the the most surprising finding of the study was the patient's behavior when exposed to snakes and spiders.
For many years, the patient told the researchers that she hates snakes and spiders and tries to avoid them, yet she immediately started touching them at a pet store, claiming she was overcome with curiosity.
"Without our amygdala, the alarm in our brain that pushes us to avoid danger is missing. [For example], the patient approaches the very things she should be avoiding, yet, strikingly, appears to be totally aware of the fact that she should be avoiding these things. It is [actually] quite remarkable that she is still alive," he added.