Nicholas Carr's book "The shallows - What the internet is doing to out brains" is a little old (2011), but an eye-opening read.
"One thing is very clear: if, knowing what we know today about the brain’s plasticity, you were to set out to invent a medium that would rewire our mental circuits as quickly and thoroughly as possible, you would probably end up designing something that looks and works a lot like the Internet. It’s not just that we tend to use the Net regularly, even obsessively. It’s that the Net delivers precisely the kind of sensory and cognitive stimuli—repetitive, intensive, interactive, addictive—that have been shown to result in strong and rapid alterations in brain circuits and functions. With the exception of alphabets and number systems, the Net may well be the single most powerful mind-altering technology that has ever come into general use. At the very least, it’s the most powerful that has come along since the book."
He's railing about the internet being a designed distraction machine, rather than youtube specifically.