Are teen brains better for multi-tasking?

>>> a new study out tonight which, as they often do, tells a lot of folks what we already know. this one says when you get older multitasking gets tougher. the younger you are, and it's called life in 2011 , and now there's a new major study looking at how all of that, all of the electronics affects the brain of the average teenager. nbc news chief medical editor dr. nancy snyderman has the first of two reports on the teen brain, a work in progress .

>> reporter: it's after school at the cohen house . a sea of computers, cell phones , and notebooks. it's how homework is done these days, with constant text messages.

>> you don't know if it's work, if it's play, if it's homework or if it's chatting.

>> reporter: a generation that has never known a world without the internet or cell phone .

>> sometimes i'll fall asleep with my phone with me in bed. i'll be just like holding on to it.

>> reporter: and the headlines reflect the concern. are we raising kids who are constantly distracted by technology? the average child now spends 7 1/2 hours a day with media. but since some of that is done with multiple devices, it's actually almost 11 hours of media every day.

>> a lot of the memory system --

>> reporter: that's why neuroscientist jay gidde is scanning the brains of thousands of teenagers.

>> this is an incredible gusher of information pouring into the teen brain from all these different sources.

>> reporter: it's a critical time for the brain, becoming more specialized by getting rid of information it doesn't use. it's like pruning branches, allowing the brain to strengthen the connections it that will last until adulthood. the doctor scans the teens every two years as they grow up and tests their distractibility. the surprising news? all this multitasking might be making their minds stronger and serves as a cross-training exercise for the brain.

>> there does seem to be a mass advertisety for the younger adolescent that allows them to get better at multitasking to a point.

>> reporter: and dr. gieg also sees this outside his lab. he's a parent of three teens himself. but he limits how much screen time his kids get.

>> as a parent we all want to do the best for our children. how do we parent better? how do we live better?

>> reporter: it's that balance, he says, that will help teens learn in this everchanging world.

>> the doctor's poor kids are under constant scrutiny.

>> constant scrutiny.

>> first of all, i find it believable that it's at some level probably good brain exercise. but do we know enough to do any long-term studies?

>> that's exactly where they're going. in fact, dr. gied says right now if you look at college kids there are no alarming findings their brains are turning into mush. they seem to be handling this incoming data, and that pruning seems to be working. so for parents keep your eyes on their grades, and one thing we're really going to talk about, and that's tomorrow night, brian, is the sleep deprivation . because sleep absolutely has an effect on the brain, and that's going to be the subject of tomorrow night's segment.

>> all right. nancy snyderman , as always, thanks. and by the way, we should point out, much more on this topic on the web. dr. nancy will host a live chat tomorrow afternoon on nightly.msnbc.com. but she won't be performing any primary care.