I'll tell you right now - the thinning of the cortex has little if anything to do with the screen. The cortex is the primary repository for memory. The screen is incidental. What matters is the information. Kids aren't taught to memorize so much as they are conditioned to search for information online. Why bother training a mind to develop memory encoding and recall when the internet can perform that function for us? If this trend continues, who's to say we'll even remember who we are in a generation or two. The most common search phrase will be "who am I?" I'm sure our benevolent overlords will then be more than happy to provide an identity that suits their goals. Digital information technology can easily be abused to direct the bulk of our species into developing as a hive mind. Those at the top will retain their identities. We have only ourselves to blame.