These types of brain chemicals are similar to the active ingredient of cannabis, tetrahydrocannabinol, and routinely circulate in memory-related areas of the brain. However, little has been known about their effects on behaviour up to now.

To investigate the function of cannabinoids in memory, researchers from the Max Planck Institute of Psychiatry, Munich, used mice that were deficient in the cannabinoid 1 (CB1) brain receptor and compared them to normal mice acting as “controls”.

The scientists used a test of memory, in which the mice were conditioned to associate a particular sound with a mild shock. The researchers found that CB1-deficient mice had significantly impaired short- and long-term extinction of memories, being less able to forget the traumatic event than control mice.

The research team also found that, during memory erasure, the brain’s fear centre, the amygdala, is flooded with cannabinoids. Their results showed that the cannabinoid system contributed to selective dampening of certain electrical pathways in the amygdala.

The study authors suggest that these natural chemicals are needed to erase fearful memories from the brain.

“It remains to be shown,” the researchers conclude, “whether CB1 is not only involved in extinction of aversive memories but also in adaptation to aversive situations in general and/or in extinction or memories, independently from their emotional value.”

Drugs that boost cannabinoids in the amygdala could, therefore, help people who suffer from anxiety conditions, such as post-traumatic stress disorder, phobias and panic attacks, say the researchers.

The research is published in the current edition of the journal Nature.

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