Extended life brains, could we build them with stem cells?

When you look at MRI scans of people in multiple stages of life, as they get older areas of the brain will begin to darken. What I mean by that is that activity starts to decrease as cells get old, weak, and eventually do not function properly.The thing about stem cells is that they will naturally take on the genetic code of the next associated cell. Cells are set up to transfer the code for what the cell next to it is supposed to be. So, what if you opened up the brain pan and replaced the damaged neurons one by one? Starting at the deepest point of damage, starting with the first damaged cell in an area and worked out in a spiral taking one stem cell at a time and replacing it where the damaged neuron had been. Then wait for it to take on the proper cell structure, then do the next one. Perhaps a job for nanobiomechanisms.
Answer:
What you're talking about is very interesting, but not really possible. First, neural stem cells are not really existent, and are only really seen in the olfactory region -- however, these are now being seen as potential candidates for neuron therapy. Second, it's unfortunately not as simple as removing one neuron and putting in a stem cell to replace it -- neurons travel extremely-convoluted paths that must be precisely reestablished in order for the stem cell to work as a functional neuron. Each neuron forms synapses with tens or hundreds of other neurons, all of which must be reestablished for them all to function appropriately. Their developmental paths and synapses are originally regulated by innumerable intercellular interactions, hormones, and circulating factors during in utero embryogenesis -- these environmental influences are not currently fully-understood nor replicable/repeatable, so the probability that an implanted stem cell would even travel the correct path and establish functional synapses with target cells is unlikely, at best. Even partially-damaged axons usually don't grow back down the correct path they were intended, and result in blind, non-functional synapses, or worse, neuromas (very painful to have)Third, your added details about how it could be done is somewhat fictional because the immune system is not under regulation of the brain, and functions rather autonomously via circulating lymphocytes and leukocytes that respond to foreign cells/tissue. The only way to achieve that kind of prolonged non-immunity is total immunosuppression, which is essentially like giving the patient AIDS. Within a hospital setting, infection would be inevitable and unstoppable without any immune system to defend the body -- antibiotics can only do so much, and they require a working immune system to be effective. This is currently a big problem with any kind of organ transplant surgery, and it's always a careful balance between immunosuppression (to prevent rejection) and opportunistic infection.So, though a very intriguing topic (and one that is being intensely investigated), I'm afraid those complications I've mentioned are the current obstacles to effective neuronal replacement, and kind of preclude the therapy you've postulated.

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We may not even need stem cells, the new neurons are already in our head, they're just losing their way and hanging out in the wrong parts of our brains.

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I found some good information on stem cells as well as the research and benefits of it etc here http://wiz.sc/stemcell. Seems to have some good advice and should help you.

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