It is concerning. I've been concussed by a baseball to the head as a teenager and these emerging long-term effects to the brain kind of freak me out. Probably shouldn't have took a few more headshots after that, but tis life I guess. Funny how our strongest asset is also the most fragile.
Finding the balance is a struggle for me. Is increased risk of dementia and other disorders when I'm older worth it for me to continue mountain biking while I'm still young? I don't know. What risks are worth taking?
Here's something I don't get about some high-risk sports: is the feeling you get doing that really irreplaceable? Aren't there a ton of other things which given some time would be just as fun?