researchers finding in a new study that even occasional casual use, once or twice a week of pot can lead to brain abnormality. so what specific impact does pot have on the brain? joining us now is the co-sponsor, author of that study at northwestern psychiatrist. joins us today. sir, got a question for you, there is a lot to your study. what's the headline? >> first off, it's a privilege to be here and thank you for just being willing to talk about this issue. the headline is that there is a folklore idea out there that casual cannabis use doesn't hurt you. well, our data directly goes against that and suggests very strongly that we need to be very careful about how much cannabis is used by people, especially when they're young, young adults. >> in reading your study, what you found is that marijuana impacts the parts of your brain that impact emotion and