There are no pain receptors in the brain. A very good friend of mine had 16hrs of surgery on his brain after a car smash with no anaesthetic, other than a local whilst his scalp was "peeled back" and he was trepanned, after a cage was screwed into his skull to keep his head static. He claimed not to have been in any pain at all during this but it needed to be done to repair multiple "bleeds" in his brain without causing any further damage. Mick used to delight in showing people the ring of bolt holes which were the only visible signs of this op and I was one of the few who didn't go a bit green at the sight. Needless to say he made a full recovery after about 18 months and has no damage other than a big gap in his memory as to how how the smash occurred but remembers the surgery and recovery in full detail