Not just the brain, but in other tissues. Some speculation as to functional aspects, which may or may not have anything to them. It's a short but interesting article: http://www.scientificamerican.com/article.cfm?id=scientists-discover-childrens-cells-living-in-mothers-brain
Wow. I had known that cells of the mother are expected to be found within her children, but that's the first I hear of it going the other way. And the idea that my younger brother may contain cells of mine as part of his living matrix is strange indeed. Does make for some interesting story thoughts. I can't help but again be reminded of Greg Bear's Darwin's Radio...
Considering the fact that i am a young woman and will likely have my own kids someday, i am both surprised and not surprised. It only adds to the bond between mother and child, and makes me wonder why today's society in some countries try to resist that. We are all people, regardless of race, so why do we try to think of ourselves as separate beings to begin with? we are very strange creatures indeed.
I really doubt this would have any emotional results, as people are suggesting, but it is pretty interesting.