Okay, that's a good question.
What you're actually seeing is a PET image—that's positron emission tomography. In that type of analysis you inject a radioactive ligand that traverses through the blood and ends up in the receptors in the brain. The receptors that you're seeing light up in that graph are what's known as the CB1 receptors. These are the cannabinoid receptors, the endocannabinoids. They are receptors in the brain that bind to marijuana-type molecules. The brain produces endocannabinoids, endogenous marijuana-type molecules that it uses in its circuits. What you are seeing there is an injection of a ligand that's binding to those receptors. You can see that those receptors are much more abundant than you would see in non-traumatic brains, which are the other two controls that you see on the right-hand side.
What's very interesting about this is that, as you know, of late there has been a lot of discussion about the use of marijuana by veterans, and a lot of anecdotal evidence indicates that they get relief from some of their symptoms by using these drugs.
What concerns me is that there is no large-scale clinical trial that actually shows the efficacy and safety of using marijuana and marijuana derivatives in the treatment of post-traumatic stress disorder. I think this really needs to happen sooner than later.