After indulging in the articles and other peers responses, I have made the conclusion that fear is driven by the amygdala, a grouping of nuclei found in the medial temporal lobe. The amygdala is attached to the hippocampus, the area in the brain where memories are developed and stored. Therefore, the amygdala's main functions are memory and emotional feelings. Fear would fall into the category of both memory and feelings.
After hearing the professor and another peer tell stories of being frightened by a dog either attacking them or scaring them, I had a similar experience myself. I personally was not affected, but a young neighboring girl was.
I have a small, very friendly dog that enjoys any humans company. One afternoon, my roommate went out to his car, but unknowingly left the back door open and my dog ran out following him. Upon leaving the house, he noticed a father and daughter outside, so being a friendly dog he started to quickly walk over to the neighbors.
However, the young daughter did not notice my dog approaching her, and when he was only a few feet away she saw him and started screaming. My roommate heard the cries and ran over and grabbed my dog, but the fear had already taken over the young girl.
The young girls amygdala sensed fear and she reacted by screaming and crying. Even though my dog never got close to touching her, just the fact that something unknowingly approached her triggered her amygdala to sense fear. I hope this memory does not haunt her through her life, but since memory is a key component to the amygdala, who knows how traumatic this experience could be.