Fear and the Brain....

We are hard wired to experience fear.  It is a reaction that evolved to protect organisms against perceived threat.  The chemicals in the brain that are involved in fight or flight are also involved in the positive states: such as happiness and excitement.  
Fear is related to content.  Some people get scared with the mention of a mouse and jump on the nearest chair.  This would not affect other people but some other trigger could get them going.  (How about a snake or rhinoceros in your yard)  What happens is the amygdala sends out the reaction to the body and gets it into motion.  When there is a fear reaction, the higher brain functions can also get involved.  There is a place called the hippocampus that starts to access the problem and gets the prefrontal cortex involved.  Oh, that was not a spider but just a piece of thread.  If it is a real threat then the stress hormones and the sympathetic nervous system kick in and  the brain goes into hyper-arousal.   The body follows by increased heart rate, pupils dilate, the stomach shuts down and off we go. 
When there is a problem with the response and the brain and body don't shut down then this can lead to a serious mental health problem such as obsessive compulsive disorder.

LENS neurofeedback can help to quiet the over anxious brain.