To be 13 right now means a thumb on Instagram and in a split second on Snapchat. From Buzzfeed, to the NBA app, to Spotify, to Youtube, the iPhone is the place where all of a teenager’s friends are always hanging out. So it’s the place where she is, too. She’s on it after it rings to wake her up in the mornings. She’s on it at school, when she can sneak it. Neurologists are trying to figure out what all this screen time is doing to the still-forming brains of teenagers.