The neurotransmitter serotonin plays a key role in both the onset and in the unlearning of fear and anxiety. A research team has been investigating the underlying mechanisms. The researchers showed that mice lacking a specific serotonin receptor unlearn fear much faster than the wild type. The results of the study provide a viable explanation how drugs that are typically used for the treatment of post-traumatic stress disorder (PTSD) alter our brain activity. The ability to unlearn fear is often impaired in PTSD patients, making it more difficult to carry out therapies.