hammertime said: Can single neurons be replaced by artificial ones, perhaps nano-bots of some kind? Or could a cluster of neurons be replaced by an artificial cluster, or perhaps hooked up to a computer which replicates their function? Is this technology possible? If so, could we ever reach a point where the entire human brain is replaced by an artificial one or somehow gradually "uploaded" into a computer? Or is that just science fiction?
Generally, the paradigm in science today is that in principal, replacing neurons with any computational bit of hardware will maintain conscious experience, though it doesn’t say that it is necessarily possible to create the actual hardware. We presently take it for granted that such hardware can be created.
Chalmers has a very famous thought experiment that discusses replacing neurons with silicone chips. The experiment is based on a concept called “functionalism” which basically states:
Functionalism in the philosophy of mind is the doctrine that what makes something a mental state of a particular type does not depend on its internal constitution, but rather on the way it functions, or the role it plays, in the system of which it is a part. … Functionalism is the doctrin that what makes something a thought, desire, pain (or any other type of mental state) depends not on its internal constitution, but solely on its function, or the role it plays, in the cognitive system of which it is a part. More precisely, functionalist theories take the identity of a mental state to be determined by its causal relations to sensory stimulations, other mental states, and behavior.
Ref: Stanford Encyclopedia of Philosophy
http://plato.stanford.edu/entries/functionalism/
Here, “mental state” is referring to the physical configuration of matter (ie: neurons, molecules, etc…), signals and just the general configuration of the brain, and is generally understood to mean how that physical configuration changes over time.
Chalmers talks about removing a single neuron from a brain and replacing it with a chip. From there, the thought experiment would have you remove each and every neuron, one at a time, and imagine how that person’s conscious awareness might change.
The question arises: What is it like to be the systems in between? For those systems intermediate between me [a brain with neurons] and Robot [a brain replaced with silicone chips], what, if anything, are they experiencing? As we move along the spectrum of cases, how does conscious experience vary? Presumably the very early cases have experiences much like mine, and the very late cases have little or no experience, but what of the cases in the middle?
Given that Robot, at the far end of the spectrum, is not conscious, it seems that one of two things must happen along the way. Either consciousness gradually fades over the series of cases, before eventually disappearing, or somewhere along the way consciousness suddenly blinks out, although the preceding case had rich conscious experiences. Call the first possibility Fading Qualia and the second Suddenly Disappearing Qualia.
Ref: Chalmers, “Absent Qualia, Fading Qualia, Dancing Qualia”
http://consc.net/papers/qualia.html
Chalmers argument*, and the conclusion based on functionalism, is that there will be no change in any conscious experience had by Robot. In fact, this is the standard paradigm cognitive science works to today – though I’m not a backer of this concept. I believe the concept of functionalism is flawed, in which case, the answer to the question of can a neuron be replaced with a chip is only “no” for any neuron that maintains conscious experience, and you can’t upload a person into a computer. The argument against functionalism is rather lengthy though, so I won’t go further into detail.
*Note: I realize the section quoted from Chalmers sounds as if he believes there will be a loss of conscious experience, but that is not the conclusion he argues for.
