Marijuana's well-known effects on short-term memory may be the result of misfiring brain cells, according to neuroscientists.

Scientific American reported Nov. 20 that David Robbe of Rutgers University and colleagues found that rats given THC -- the active ingredient in marijuana -- and a synthetic cannabinoid experienced disruptions in the synchronous brain-cell firing that causes memories to be formed. The drugs also slowed brain-wave activity, notably theta and fast-ripple waves but also gamma waves.

Theta and gamma waves are believed to be involved in short-term memory formation, while the fast-ripple waves are thought to play a role in moving such memories into long-term storage.

At very high doses, the drugs appeared to prevent learning altogether.

"Overall, our findings indicate that under the influence of cannabinoids, neurons are liberated from population control," the researchers wrote in the online version of the journal Nature Neuroscience.