[yew]

Smartphone notifications certainly aren't 'known' to cause any long-term changes in the brain. The number of actual rigorous studies of the subject is tiny and results have been rather inconclusive so far. (It is known that individuals who stringently follow social media while also doing something else can be distracted by it. Fortunately that's not the only application of the technology.)

As for personal issues with notifications: You can just turn them off. I only get notifications for email that my filtering system can't handle, which means the sort of stuff that I would have had to carry a pager for before the advent of the smartphone. I get maybe a half-dozen unrelated notifications a month for spam that my filter didn't catch, and that number is going down. No Facebook or Twitter. No text messages or chats. Just the important email and actual honest-to-god phone calls.