When fear and anxiety derail: The pathology of the human defense system

From the perspective of Biological Psychology, fear and anxiety are emotional states that activate a defense system in the mammalian brain. This defense system regulates the encoding of threatening stimuli and organizes the response output to adjust to the threat. Animal data suggest that the amygdala is the core structure in this defense system. The amygdala receives sensory inputs from the thalamus and the cortex and sends efferent projections to several areas in the cortex, the diencephalon, midbrain, and brain stem. Thus, the affective system interacts with several cortical areas and cognitive functions. Pathological forms of fear and anxiety are not principally different from normal emotional responses. Rather there is a sensitization of the defense system. Therefore, defensive behaviour is already activated at a lower intensity or proximity,of the threatening stimulus. Simultaneously, the perceptual system is primed for detecting threatening stimuli in the environment, further sensitizing the defense system. In states of chronic anxiety this defense system is permanently alert, scanning the environment for potentially threatening cues (these can also be interoceptive cues) (hypervigilance), and also priming defensive behavior and increasing autonomic arousal.