Traumatic memories are hard to shake and can become intrusive, leading to conditions such as anxiety and posttraumatic stress disorder. An international research team has now discovered a possible explanation for the lasting power of painful memories by taking a close chemical look at rat behavior (Science 2009, 325, 1258). As in humans, traumatic memories persist in adult rats. But in young rats, such memories can be erased. Andreas LÃ¼thi of Friedrich Miescher Institute for Biomedical Research, in Basel, Switzerland; Cyril Herry of the French National Institute for Health & Medical Research, in Bordeaux; and colleagues found that as a rat matures a network of chondroitin sulfate proteoglycans forms around nerve cells in the amygdala, the brain region that controls traumatic memories. When the team destroyed the net with an injected enzyme, adult rats regained the ability to forget traumatic memories. If the findings apply to the human brain, a strategy for preventing pathological memory conditions could be developed, the researchers conclude.