There is a study listed in the Journal of Neuroscience that shows certain electrical switches in the brain, known as L-type voltage-gated calcium channels (LVGCCs), are required to overcome fear. These switches only allow you to "unlearn" or conquer a specific fear or phobia.
Right now, behavior therapy is "the most efficacious treatment for human anxiety disorders," the researchers write. And they say "this discovery holds out hope for the development of new drugs that can make such therapy easier. The findings appear in the Oct. 15 issue of the Journal of Neuroscience. http://my.webmd.com/content/article/52/49979.htm?lastselectedguid={5FE84E90-BC77-4056-A91C-9531713CA348}