The study also teased out why this brain inflammation leads to motor and learning problems, and found a surprising answer — cannabis activates immune cells that appear to play a critical role in how a brain region called the cerebellum works.

In the study, mice were given delta9-tetrahydrocannabinol, or THC, the active ingredient of marijuana, for six days. Then the mice were required to perform several tasks to test their coordination, as well as their ability to learn to associate a sound with a puff of air to the eye. During the latter task, called eyeblink conditioning, mice should learn to anticipate the air puff, and blink when they hear the sound.