This is your brain on drugs, according to Peter Hess of Inverse, who teamed up with specialists to take a look at several functional magnetic resonance imaging (fMRI) scans of cannabis consumers to find out exactly what happens in your brain, before, during and after smoking marijuana.

Before You Light Up

Marijuana changes the way your brain works before you start smoking. The process of deciding to consume cannabis alone begins the chain of changes in brain activity that you will undergo during your sesh. When you decide to smoke weed, several parts of the brain that regulate reward and motivation light up as well as ones that calculate risk.

"When a person decides to smoke weed, they're essentially performing an analysis of the value they'll receive by smoking and whether that value is worth pursuing," reports Peter Hess of Inverse.

"If smoking is deemed a good choice, the brain determines how to perform the act. It's a complex pathway for a simple choice, but it's a pattern of activation that's uniquely tied to smoking weed."

This process is so unique that researchers can distinguish the fMRI of smokers versus non-smokers with 100 percent accuracy. And it's not because their brains look like a fried egg, as old PSAs would have us believe.

While High

There are three areas of the brain that receive a decrease of blood flow, which makes them prone to under-performing when you get high. These are the insula, the striatum and the dorsomedial thalamus.

"The insula is associated with initiating actions based on physical state, and the striatum is associated with reward and decision-making," Hess explained. "The dorsomedial thalamus is involved with memory and cognition."

Those findings suggest that stoned people may have greater difficulty figuring out the importance of what they are looking at and what to do about. Hence it's a bad idea to drive while high. If you see a pedestrian on the street it could take more time to figure out that a) that you might hit that person, and b) what you can do to not do that. And those extra seconds could prove lethal.

The change in blood flow can also explain why you sometimes feel stuck in your own head when you get high. The reduction of activity in the brain areas basically make you predisposed to focus on your own internal thoughts.

What is really fascinating is that some of this brain activity actually starts in the decision making process and carries through until you come down.

Longterm Effects

So, what does the brain of a longtime marijuana consumer look like versus that of some one who doesn't smoke? Well, quite a bit different actually. 

Longterm consumers tend to have "less gray matter in the bilateral orbitofrontal gyri, which are associated with making decisions and processing emotions," Hess noted. But since your brain tries to find ways to compensate for the lost activity in one section by boosting activity elsewhere, cannabis consumers tend to have "more structural connectivity in the orbitofrontal cortex network" than non-consumers. 

While researchers don't know whether or not these kinds of long term changes in brain structure are necessarily positive or negative, there's no question that every time we answer one question about our little plant, two more crop up.