More than 30 years ago, scientists discovered that mad cow and Creutzfeldt-Jakob diseases are caused by prions. But in recent years, Nobel laureate Eric Kandel, M.D., demonstrated in mice that some prions are beneficial and serve important functions in the brain and body. And today, new research from Dr. Kandel describes how one such prion-like protein helps the brain keep fearful memories in check. Without it, female mice exhibit the tell-tale signs of post-traumatic stress disorder, or PTSD.