Marijuana use has long been known to cause problems with learning and memory. Now, researchers at the Albert Einstein College of Medicine of Yeshiva University have identified the mechanism by which marijuana may affect activity in the hippocampus, the portion of the brain responsible for learning and memory. They reported their findings in the September 16 issue of the journal Neuron.
The active chemical in marijuana, THC, is also present in marijuana-like molecules called endocannabinoids that occur naturally in our brains, explains Dr. Pablo Castillo, associate professor of neuroscience at Einstein. These naturally occurring endocannabinoids are neurotransmitters that send signals between neurons in the brain, permitting the intake and storage of information that is critical for effective learning and memory. This communication process between neurons is referred to as synaptic plasticity. (Synapses are the gaps between nerve cells into which one nerve cell secretes a neurotransmitter that stimulates the adjacent nerve cell; and synaptic plasticity refers to the ability of these impulses to pass between neurons.)
But Dr. Castillo notes that when cannabinoids are introduced from outside the body through marijuana use, they serve to short circuit the internal system and impair synaptic plasticity in particular, thereby interfering with the way neurons signal one another, gather information, and store it.