Post-traumatic stress disorder (PTSD) is an anxiety disorder that can develop after exposure to a terrifying event or ordeal. While many scientific studies focus on the molecular mechanisms for learning and memorization, scientists need to address the “unlearning” process to tackle PTSD. Researchers have discovered that a receptor for glutamate, the most prominent neurotransmitter in the central nervous system, plays a key role in the unlearning process. They made this discovery in experiments where they trained mice to fear a sound by coupling it with an electric shock to the foot. They found that if, following this fear conditioning, the mice are repeatedly exposed to the sound without the electric shock, their fear eventually subsides. However, mutant mice lacking the gene-coding for metabotropic glutamate receptor 5 (mGluR5) are unable to shake off their fear of the now harmless sound. The researchers believe that a similar mechanism might be perturbed in PTSD sufferers and that metabotropic glutamate receptor 5 (mGluR5) may provide a potential target for new therapeutic treatments.