Questions like the one you have asked and numerous similar others have always fascinated man since time immemorial. If we truly ponder over life's mysteriously enigmatic existence, we will have a never-ending list of those questions to which there will be no convincing answer. But before you ask these questions, just ask this one to yourself, "Who am I?" If you are truly able to find a convincing answer for this question, then you will be able to find the answers for all the others you have asked.
Brain, Mind, Consciousness.....its NOTHING!!! because EVERYTHING IS NOTHING!!!. You try to zoom IN and OUT of human life and you will reach the farthest end beyond the DNA, on one side and much more farther than the galaxies on the other side. So reaching the extremes, what do you think we are?...NOTHING!!! Then WHO AM I???!!! :)