Brain Chemicals May Calm Bad Memories

Frightening or painful memories may be calmed or even erased by marijuana-like chemicals produced in the brain, according to a study of mice chronicled in Thursday's issue of Nature. Mice bred to be unresponsive to the chemicals, called cannabinoids, couldn't control their reaction when they heard a reminder linked to pain. Normal mice eventually stopped flinching at the reminder. The brain naturally produces cannabinoids in response to pain and fear, which might have helped the normal mice recover, researchers said.

New treatments for anxiety disorders and post-traumatic stress syndrome might be developed based on the cannabinoids, which are also the active ingredient in marijuana, said Beat Lutz of the Max Planck Institute of Psychiatry in Munich, who led the study.