and those who smoke after age 16. what we call early versus later onset. >> gruber's brain scans show the white matter, those are the highways that help the brain communicate from one point to another are impaired in those who start smoking early. >> maybe that there's underlying white matter connectivity differences. >> that's your concern, it sounds like, that those highways, those white matter highways are just more disrupted in people who start smoking early. >> that's what we see. >> perhaps not surprising given what we know about the young developing brain. >> that's a very delicate time in brain development, and that's not a good time to be taking any drugs. >> preliminary research shows that early onset smokers are slower at tasks, have lower iq's later in life, higher risk of strokes, and increased incidents of psychotic disorders. while these studies are not conclusive, some scientists are still concerned because in 2012 35% of high school seniors lit up, and that could mean a generation of kids with damaged brains. many fear something else. >> i never really told myself i needed help. >> a generation of marijuana addicts.