Youths smoke marijuana at the Denver 4/20 pro-marijuana rally at Civic Center Park in Denver, Saturday, April 20, 2013. 

(AP Photo/Brennan Linsley)

Scientists know that adolescence is one of the most important times in life for brain development. It's also a time when some children experiment with various drugs. What scientists don't know is how much drugs impact the development process during these years, versus how much of a role genetics plays.

Marie Banich directs the Institute of Cognitive Science at CU Boulder. She's part of a new, nationwide study of how drugs -- including marijuana -- shape the adolescent brain. The study will follow about 10,000 young people starting at age 9 -- before it's likely they've done drugs -- and through their teenage years.

Banich spoke with Ryan Warner. Click the link above to hear the full interview and read edited highlights below. 

Why more research is needed on adolescent drug use:
 
"When we look at the brains of adolescents that have taken drugs, we can see that they are different than the adolescents who haven't taken drugs. The question is, is it really the effect of the drugs itself, or is there a contribution from, for example, if we could've looked at their brains before they started taking drugs, would their brains have looked different from the get-go due to genetic influences."
 
Some kids won't try drugs: Why study them?
 
"Because if we see that drugs have an effect on the brain, we can look for what is called a dose-dependent effect. What that means is we should see more brain changes for those who've used lots of a drug, intermediate changes for those who haven't used that many drugs, and not so many brain changes for those individuals who've used no drugs." 
 
How the findings may impact public policy:
 
"Let's say we find that the largest influence [for drug use] is genetic. That might suggest that what you might want to do is to try to find those individuals who might be genetically at risk for substance abuse and target most of your interventions and educational programs towards them.
 
On the other hand, let's say we find the major factor is really how many drugs you've taken. Well, then that suggests that what you'd like to do is really have a broad-based program to teach teenagers about the effects of drugs and to disabuse them of false ideas. [...] If it turns out the amount of drugs you take are really important, then that teenager would really be working under a false thought and wouldn't realize the danger he or she would be in."