This is so much fun! Met my first Objectivist (Tim) years ago and we fell madly in like! I was (am) a fairly orthodox Christian and he was (is) an Ayn Rand acolyte, non pariel. We had a discussion along these lines (and I'm short on time and a little ADD, so I did not read EVERY SINGLE entry, but enough to know the gist of the discussion), and eventually the question arose, "Is the mind the brain, or is the mind OTHER than the brain?" Of course, Objectivism being a pretty pure form of Naturalism, there can be no difference: they are one and the same. So I ask this guy, "Okay, Tim, where does 'thought' come from?" He said that, according to all the available "science" of the brain/mind, every "thought", and by default, every action, is the result of purely "electro-chemical [i.e.,physical, material] stimulation initiated in the brain", therefore, all thought and all action is PURELY physical, nothing metaphysical about it. So I say, "Okay, what is the prime stimulation? What is the 'initiation'?"
"What do you mean?"
"Well, what 'starts', 'fires', the first thought that precedes any--every--subsequent action or 're-action'? Is it purely a previous physical thing, within your physical 'machine' that is itself simply the re-action of a previous 'stimulation' and so on and so on?"
"Well, yes, of course."
"Then you are nothing but a pre-programmed [which is funny since there's no Pre-programmer!] machine, like an extremely complex series of lined up dominoes, or, dare we say, a robot or computer [with no programmer]! Your beloved 'free will' by default either does not exist, OR exists OUTSIDE the purely physical confines of your material brain, and therefore allows for the existence of the metaphysical. QED, the mind is the physical brain and there is no free will, or the mind is separate from the brain, thus allowing for free will."
In the interest of intellectual honesty, he had to choose the former, but subsequently retracted said choice since it didn't square with his view of free will. "I'll have to get back with you on that." Alas, we lost touch and 'so it goes...'