Personnally Id get use to getting hit with 16 oz gloves then work your way down to 8oz but not full blown, its really how to bob and weave you are learning in training. You are going to get hit at somepoint in you career, but if it doesnt knock you out your adrenaline will help you through unless you get shook, which tends to cause you to curl up and defend which normally ends up end the fight with the ref stepping in because you cant respond to any of the hits.
As for brain damage its one of those things where its not that common in mma unlike boxing, where they continuously are getting hit and over the years of constant pounding it causes brain damage. In mma my friend had a freak of accident where he got hit hard in training and the way that he fell forced him to not fight for 6 months. It can happen but less unlikely in mma than boxing, because in mma the padding is thinner so if you get hit only take one or two punches where in boxing its 12 rounds