First posted 27 Nov 2003. In the original post, I reduced the mind - all mental states - to the activity of the brain - changes in brain states. Mind was therefore emergent and causally redundant. It was, perhaps, the greatest of Jay Gould's 'spandrels' in evolution.
Today, I am certain that my mind, or at least a current mental state, exists. I am open minded (ha!) with respect to its relation to a brain, but I tend to think that the causal connection, if there is one, is opposite to what is described below. Has there been re-wiring???
The human brain is a busy place. We each have about a trillion brain cells. 10% of these are neurons, which transmit and receive electro-chemical signals, and 90% of which are 'support' cells. Each of the 100 billion neurons actively communicates with 1000 - 10,000 others.
100 billion neurons, each of which can be 'on' or 'off', can generate 2^100,000,000,000 (or roughly 10^30,000,000,000) unique brain states. It is now a well worn comment that this is greater than the number of particles in the universe. I don't know whether that is true or not, but I know that 1 followed by 30 billion zeros is a bloody huge number. If all six billion people alive today each cycled through a million unique brain states every second, and if we 'thought' at that pace for a duration equal to the age of the universe, we would only have jointly 'hit' 10^33 different brain states. We would still have 10^29,999,999,967 to go! And even if 99.999999999999999999% of those possible brain states weren't really compatible with normal human operation, we would still have 10^29,999,999,947 left!
These neurons and their support cells are organised into functional components within the brain. Different bits within the human brain have developed specialties (e.g visual processing, abstract reasoning, motor control). That is not to say that these components are 'one trick ponies' - bits of the brain do re-wire themselves to take on new tasks when other bits are damaged by injury or illness. It is also not to say that the brain's activity can be wholly explained in component terms - for instance, consciousness may be best explained as an emergent property of the complex interactions between as well as within functional 'organs'.
About a third of our 30,000 genes are dedicated to building and operating our brains. These genes 'hard-wire' a fair bit of functionality, including sensory processing, autonomic regulation and portfolio of predispositions. They also construct a brain with a ready-made template for acquiring language and indeed an innate capacity and drive to learn in general. The genetically-driven construction and regulation of the brain is itself environmentally sensitive - in some cases even environmentally driven. But the neuronal complexity of the working brain allows for behavioural flexibility on an entirely different level - more than the world has yet to see or ever will exhaust. It is that flexibility which has allowed us to populate and thrive in nearly every environmental niche nature has to offer.
Where does the brain stop and the mind begin? I've said above and in other posts broadly what I believe on this front. The mind is an emergent phenomenon of the complex activity of the brain. Brain states themselves result in part from body mapping. Sensory (sights, sounds, touches, smells, tastes) and visceral inputs (heart rate, blood sugar levels, body temperature, adrenaline levels, etc) are 'mapped' to designated brain regions and drive the neuronal states of those regions. This body mapping to the brain interacts with other brain activity (in the sense that the neuronal states associated with the mapping explain less than the entire neuronal state of the brain), and the aggregate brain state corresponds to (and causes) a mental state. Antonio Damasio points out that perhaps this is what Spinoza meant when he said that the mind was 'the idea of the body'.
So, mental states correspond to brain states, which are partly determined by body states. I believe there is a causal relationship and that it is one-way only. Mental states do not affect brain states but are always determined by them. In that sense, mental states are redundant. Everything we do, we could do without consciousness, without sentience.
Why and how did the mind evolve, then? Some would argue that mental states did bestow competitive advantage in survival and reproduction, but that is not consistent with my view. In my view, it conveyed no competitive advantage but arose once the complexity of the brain's activities passed a certain threshold. The brain's functions conveyed advantages, so it is easy enough to postulate its evolution. Then we just say that from the incredible complexity of the brain (remember those 100 billion neurons?), flows a new, subjective perspective, a by-product of evolution - the mind.
My mind is not all that I AM. I am much more than that, reaching both forward and backward from my human life and sentient existence. My mind IS my experience, my perspective. I am the only person with access to it. It is real, but it is not above the physical, causal, determined world. It is rooted in that world, via my brain and the rest of my body.
But just because I say that the mind only exists at the end of causal branches, never in the middle or at the root of them, does not mean that the mind (which I am roughly equating to subjective experience) is not important. It is tremendously important in two ways. First, each mind, each subjective perspective, is of immeasurable importance to the person to whose brain the mind corresponds. Second, through the emotion of empathy, we care about the subjective experience of others (at least those close to us) because we put ourselves in their shoes and can imagine what their subjective experience feels like. In general, we don't want others to have to experience pain and suffering and we want them to experience joy and love.