NOVA

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Narrator

During adolescence, our natural endocannabinoids reach their highest levels as the brain rapidly changes. It's also a time when many first try cannabis. So when one consumes THC, you're basically indiscriminately activating all your cannabinoid receptors in your entire body and the entire brain. So THC, it's like a hammer on all of these receptors. Our natural endogenous cannabinoids are never these hammers. -

Narrator

To understand the impact of cannabis, clinical psychologist Joanna Jacobus has scanned over 1000 teenage brains to search for differences between those who use the drug and those who don't. Today, she's evaluating Angel, who has smoked cannabis at least once a week for the past year, and is curious to learn about its impact. All I needed to really hear is like, "Hey, do you want an MRI of your brain?" Yes! Like that to me, that's, like, really cool. I know it's nerdy, but, like the substance you're doing. You don't get to see what it does to your brain. Using functional magnetic resonance imaging, Jacobus can study brain structures that are critical for healthy development in young adults. The brain is rapidly changing from infancy through childhood, adolescence, into young adulthood. Two types of tissue are rapidly changing that support cognitive development. So, gray matter contains the cell bodies and makes up the cerebral cortex, so the outermost lining of the brain. And white matter allows gray matter regions to communicate quickly and efficiently. -

Narrator

During the teenage years, white matter increases and gray matter diminishes, as weaker neural connections are eliminated and new ones form to make the brain more efficient. Jacobus has found that teen cannabis users have a thicker cerebral cortex, suggesting that this pruning of synapses has been disrupted. -

Jacobus

Now, I'm going to read the same list again. -

Narrator

And it's not just physical brain changes. -

Jacobus

I want you to tell me as many- -

Narrator

Thousands of cognitive tests, reveal that teens who use cannabis regularly struggle more on learning and memory tasks than those who don't. -

Jacobus

Bull, dinner, mug- It made me realize that memory is probably the biggest thing that impacts me with cannabis. But definitely, if I stop for a little bit, I have a feeling that it would be easy to remember those things. -

Narrator

Research shows after a period of abstinence, cognitive performance can bounce back. And the brain changes? Other studies link them to alcohol or genetic and environmental influences. It is possible that cannabis itself is not the culprit, that these differences that we see in the brain are preexisting and that they come before a child ever picks up their first joint.