The Real Stuff
There are excellent philosophical reasons to assume that mind is the primary stuff of the universe. It is the only stuff we experience directly. The physical world we apprehend only by way of mind: it's tiresome and trite to insist on, but until people get it, we have to keep insisting on it: we don't experience the physical world. We experience the images of the physical world that our mind creates. We know that all of these images are inadequate, and some -- the ones we experience while dreaming -- appear to be completely made up. The physical world is not the primary, bedrock fact we deal with. The primary, bedrock fact is awareness. It is not hardheaded to believe in the reality of the physical world: it is, rather, a leap of faith.
It's a leap I'm happy to make. I believe the physical world is real, every bit as real as my own mind. What I don't believe is that my conception of it is anything but a crude cartoon, a drastic oversimplification, tailored to my own capacities and obsessions. And I don't think it's a settled question whether mind or the physical world, or either, is primary -- which generates which, and how. We simply don't know.
Consciousness appears to vanish when brain activity ceases, and perhaps it does. But that doesn't necessarily mean that brain activity creates consciousness. When you draw down blackout shades, to all appearances the sun vanishes: but that doesn't mean that the open window creates the sunshine, and it doesn't mean that the sunshine stops when you draw the shades. Correlation is not causation.
I am perfectly happy to entertain the hypothesis that brain activity creates consciousness. What I'm not happy with is to accord this hypothesis the status of scientific theory. It does not account well for some of the basic facts of our experience. Why are we aware of our own thinking? Why do we have a sense of self? Why these persistent experiences, across an incredible diversity of times and cultures, of divinity, and of crossing the limits of the individual mind? It's possible that all these things are accidents, by-products of the evolution of the brain. Accidents do happen. But that's not the sort of explanation that gives you confidence in a theory: it sounds much more like desperate speculation than like solid reliable understanding. A theory of what consciousness is ought to account for the facts of consciousness. I don't think the materialist hypothesis, to date, does that very well. Which doesn't mean it's wrong, of course: it could just be incomplete. But I do find it irritating when people take this hypothesis to be as well grounded and thoroughly proven as the theory of gravity, or the theory of evolution.
What would I take as proof? Well, for a beginning, someone should be able to produce a specific thought by a specific physical intervention in the brain. Someone should be able to stimulate a physical path of neurons that produces, for instance, the thought that "two plus two equals four," or "stars are distant suns." Propose that to any neuroscientist and see if they think they're going to be able to do it soon.
Somebody will no doubt bring up the ape who appeared to see something fluttering around its head when its brain was stimulated in a certain way. That is, indeed, extremely interesting, but it's doesn't really bear on this question. No one (that I know of) has ever denied that the physical brain and the mind influence each other. There wouldn't be much point in having either, if they didn't. The question is how they influence each other, and if one is the origin of the other. That's what we don't know.