Brain's Marijuana-like Chemicals Help you Forget

New research published this week suggests that cannabis-like substances made by the brain play a role in helping us to forget bad memories. Beat Lutz and his team at the Institute of Psychiatry in Munich genetically engineered mice so that they no longer made a receptor called CB1, which is needed to feel the effects of cannabis. They then trained the modified mice, together with normal unmodified mice, to expect a small electric shock when they played a musical tone. Both groups of mice learned the association very quickly, and showed signs of fear - freezing - whenever the tone was played. The researchers then stopped giving the electric shock and just played the tone. The normal mice very quickly stopped reacting to the tone, but the modified mice took 6 times longer to stop freezing whenever the tone was played. When the researchers looked at the brains of mice as they were unlearning the unpleasant association, they found high levels of the brain's own cannabis-like substances, suggesting that these chemicals help to erase bad memories. These findings might help us to develop new ways to help patients with mental illnesses caused by unpleasant memories, including phobias and post-traumatic stress disorder, say the researchers. It might also help to explain why people with mental illnesses are much more likely to be marijuana users than healthy individuals, and to explain why cannabis has been found to be bad for your memory.