| STUDY |
In a healthy brain, painful memories fade away over time. A key regulator of that process, at least in mice, may be the naturally occurring marijuana-like chemicals known as endogenous cannabinoids. Authors studied mice that had learned to associate a particular sound with a foot shock. Normal animals that repeatedly hear the sound without receiving the shock eventually forget the association. The researchers found, however, that mice genetically engineered so that they do not have one type of cannabinoid receptor are unable to forget the painful association once they learn it. The same effect occurs in normal mice treated with a drug that blocks this receptor. Hearing the sound without the shock consistently raised the levels of endogenous cannabinoids in the part of their brains known to control memory extinction in both normal and engineered mice. The findings suggest that marijuana and similar compounds that activate cannabinoid receptors may be useful for treating diseases such as post-traumatic stress disorder and phobias that involve reliving painful memories.
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