Neurobiology

The amygdala is a key brain structure in the neurobiology of fear. It is involved in the processing of negative emotions (such as fear and anger). Researchers have observed hyperactivity in the amygdala when patients who were shown threatening faces or confronted with frightening situations. Patients with a more severe social phobia showed a correlation with increased response in the amygdala. Studies have also shown that subjects exposed to images of frightened faces, or faces of people from another race, exhibit increased activity in the amygdala.
The fear response generated by the amygdala can be mitigated by another brain region known as the rostral anterior cingulate cortex, located in the frontal lobe. In a 2006 study at Columbia University, researchers observed that test subjects experienced less activity in the amygdala when they consciously perceived fearful stimuli than when they unconsciously perceived fearful stimuli. In the former case, they discovered the rostral anterior cingulate cortex activates to dampen activity in amygdala, granting the subjects a degree of emotional control.
The role of the amygdala in the processing of fear-related stimuli has been questioned by research upon those in which it is bilateral damaged. Even in the absence of their amygdala, they still react rapidly to fearful faces.
Suppression of amygdala activity can also be achieved by pathogens. Rats infected with the toxoplasmosis parasite become less fearful of cats, sometimes even seeking out their urine-marked areas. This behavior often leads to them being eaten by cats. The parasite then reproduces within the body of the cat. There is evidence that the parasite concentrates itself in the amygdala of infected rats.