Please take with a grain of salt because I am no expert here: IIRC, ADHD is caused by brains that have too many dopamine transporters, resulting in dopamine being transported faster than normal, causing increased anxiety and impulsivity.

But then there's addiction, which can hijack one of your brain systems like your dopamine or endorphine systems. In the case of internet addiction disorder, reading endless feeds must be related to dopamine for sure.