I mean the visceral shearing that generally takes place with an impact to the head. The brain doesn't turn at the same rate the skull does, or doesn't stop at the same time as the skull when hit, so the small vessels into the brain get torn. After a while, not as much oxygen gets intot he brain.
Yes, I have known intelligent articulate guys that have gotten into kickboxing over a long term and been completely changed. Personality - still nice, but not as sharp, and kind of a duller gaze. And much different in conversation, not as near articulate and crisp.
I imagine the brick would have a similar effect.