How Marijuana Affects Memory: It's Not The Neurons



Getting mice stoned can actually result in important scientific discoveries. Research published in March in Cell magazine reveal how marijuana impairs working memory, the short-term memory we use to hold on to and process thoughts. The classic example is of the stoner who forgets the point he was making, mid-sentence.

To study exactly how cannabis affects working memory in such a fashion, Giovanni Marsicano of the University of Bordeaux in France and his colleagues removed cannabinoid receptors from neurons in mice, reports Ruth Williams at Scientific American. These receptors are proteins that respond to marijuana's chief psychoactive ingredient, THC (tetrahydrocannabinol).

The mice whose cannabinoid receptors had been removed from their neurons were just as forgetful as regular mice when given THC; that is to say, they were just as bad at memorizing the position of a hidden platform in a water pool. But when the cannabinoid receptors were removed from astrocytes, a type of glial cells, the mice could find the platform just fine while on THC.

The research reveals that astrocytes have a major role in working memory, with the results suggesting that the role of glia in mental activity has been overlooked. Glial cells were previously viewed as little more than the "glue" which supports neurons.

Although recent research has shown that glia are involved in many unconscious processes and diseases, this is one of the first studies to suggest that glia play a major role in conscious thought.

"It's very likely that astrocytes have many more functions than we thought," Marsicano said. "Certainly their role in cognition is now being revealed."

Since THC's pain-relieving property appears to work through neurons -- unlike its effect on working memory -- in theory, it might be possible to design THC-type drugs that target neurons, but not glia, thus offering pain relief without forgetfulness to patients who wish to maintain their cognitive capacity.