The amygdala

The amygdala is a center of the brain associated with the perception of danger and emotional responses. When a threat is sensed, it comes into play swiftly and sounds the alarm before the body has made any conscious assessment. The amygdala prioritizes survival; this is why it can sometimes ring the alarm even when there is no real danger. This structure is one of the physiological foundations of fear and rapid reactions. The amygdala's alarm often comes before thought.