The Amygdala is a part of the brain within the Limbic system which is a primitive part of the brain.
Primitive motivations of fear and reward are generated from this part of the brain. Memories are stored in respect of emotional events. Fear conditioning where a person is repeatedly exposed to the same fear conditions will build a fear response within the Amygdala.
Our inner voices can also trigger fear and reward. When fear is detected within the Amygdala, cortisol is released into the blood stream to build the fight or flight response and increases stress. Lowering of stress occurs when the fear is removed by releasing endorphins into the bloodstream.