Can single neurons be replaced by artificial ones, perhaps nano-bots
of some kind?
No. Artificial neurons have not been developed.
Could a cluster of neurons be replaced by an artificial cluster?
No, but devices such as cochlear implants and the electrode arrays used for deep brain stimulation can perform the functions of groups of neurons.
...or perhaps hooked up to a computer which
replicates their function?
Some research groups have developed neuron-semiconductor interfaces which can communicate with neurons bidirectionally (i.e. artificial synapses). So, information from spontaneously-formed networks of cultured nerve cells has been shown to be capable of "learning" to control a flight simulator, or to navigate an artificial animal through a computer-simulated environment. Others have successfully altered the activity of cultured neuron networks by transmitting to them electrical signals using carbon nanotubes.
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?
This question is a philosophical one which people have argued about for a long time. Some say yes, others (including myself) say no. For more information, see this post about the philosophy of The Matrix, and this one.
If you have any neuroscience-related questions, do leave a comment or email me, and I'll do my best to answer them.
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Hi I'm a final year philosophy and cognitive science student. I just started a blog on philosophy of mind and cognitive science. The most recent blogs on machine consciousness in fact go into the issues you outline in this blog. I would be very interested to hear what you think. I'm also trying to get as many readers as possible to my blog, so if you post a link from your blog to mine, I will do likewise to yours:
http://www.philosophyofcogs.blogspot.com/
Much appreciated
In "The Mind's I: Fantasies and Reflections on Self and Soul" Dennet's pen is moradacious arguing that we cannot upload a mind in its wholeness because not only a brain is diferent from individual to idividual in its early structure and configuration (patterns of synaptic connections), but more important because experience changes that configuration.
So any kind of platform for reproduction, copying, storage... of a mind is ilusory. Dennett suggest that books is the only known technology to transfer minds to minds.
I haven't read The Mind's I, but that sounds to me more like an argument that personal identity (in the philosophical sense) can't survive uploading, not that uploading is impossible per se. That is, if a mind were to be uploaded, the pre-upload mind and the post-upload mind would not be "attached" to the same person, in whatever way minds are "attached" to persons, because uploading breaks some kind of continuous causal chain necessary for identity to persist through time. That's certainly a respectable philosophical position, although it does require the claimant to address the question of how the "discontinuity" imposed by uploading is qualitatively different from that imposed by, say, a traumatic brain injury, or a psychoactive drug, or neurogenesis.
I think these questions weren't about our current capabilities as much as what is theoretically possible - not whether we can, but whether it can be done at all.
The answers, then, are not accurate.
I don't deny the many advances seen in bioengineering or biomechanics, one of them called MEMS (microelectrmechanical systems) use in spine surgery compound of chips that read and respond to the enviroment in which is place with the possibility to store information or just the possibility send data (telemetry) to a parepheral device and then load and upload the activity in an artifical material thanks to algorithms and therefor help in the clinical set to mnitor or build prosthesis (bionic man). But the problem with the "self" (mind) that in philosphical terms is describe in the metaphysical issue of personal identity refers to, typically, four related phenomena: identity in time and sapce, body continuity, interdepency in memory across time and persistent against change in body. I believe that some bioinformatics platforms can upload some sort of parameters and information, readable in our physics brains, but are incapable of recreate "minds", and that's the philosophical point highlithed by Dennett. I'm not against bioengineering technology either in theory or practice but uninstall or install my younger self in my older brain or Hitler's mind in me, just because some weird nazi technologist have recreated Hitler's mind and upload it in a machine, it is too futuristic, i think.
The discontinuity imposed by an uplñoadng is not only qualitatively bt quantitavtively different. In a traumatic brain injury there are genetic,molecular, cellular signatures traceable in the physical brain of the individual that reconstruct it's inmediate past and predicts it's ongoing future, how we can do that with and artifical bioinfrmatics platform?, can we nurture an artifical platform? or just it is the case that we can load and upload information derived from a single instant of time whenever the technician desires?