Is screen time affecting kids' brains?

60 Minutes goes inside a landmark government study of young minds to see if phones, tablets and other screens are changing the development of adolescent minds. Sunday at 7 p.m. ET/PT on CBS

Early results from the most ambitious study of the developing adolescent brain ever undertaken show differences in some of the brains of heavy screen users. The data, supported by the National Institutes of Health, also found children who spent more than two hours a day on screens scored lower on thought and language tests than those who spent less time on phones and other electronic devices. 60 Minutes will report on the earliest data from the study Sunday, December 9 at 7:00 p.m., ET/PT on CBS.

Researchers at 21 sites have begun interviewing thousands of nine and 10-year-olds and scanning their developing brains. They will follow these and other participants for 10 years to determine how their brains change as they mature. The scans of 4,500 kids in the study show a thinning of the cortex in some of the brains of those spending more than seven hours a day playing video games or engaging with smartphones and tablets. The thinning is normal, but is usually expected to take place later in a child's development.

"[Thinning of the cortex is] typically thought to be a maturational process. So what we would expect to see later is happening a little bit earlier," says the NIH's Dr. Gaya Dowling. But Dowling cautions the study has only just begun. "We don't know if it's being caused by the screen time. We don't know what the consequences are. So we don't know yet if it's a bad thing.  It won't be until we follow them over time that we will see if there are outcomes that are associated with the differences that we're seeing in this single snapshot," says Dowling.

The study was originally formed to learn the effects of sleep, head injuries and substance use on the brains of youths. But the team realized there was an opportunity to learn about a newer and pervasive influence on children. "Clearly, kids spend so much time on screens," Dowling says. "The likelihood that they have an impact on brain and cognition and social development is pretty high."