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Comment by cbd1984 | Hacker News Reader

cbd1984

As it stands, there's a simple answer: The brain. The person is defined by having a specific brain; you can swap out literally everything else and the person will still be the same person.

This will be more relevant when pieces of the brain are being swapped out.

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Though I find it hard to relate to, many people consider their bodies to be essential to their identity — they wouldn't be them without it. These people find our intuition about what is essential similarly foreign.

Some people have body dysmorphia issues, and some people just really identify with looking a specific way. I understand that. However, some people really identify with living in a specific location, too, but we don't usually regard moving day as the death date of the person who moved.

To be fair, AFAIK we don't really know how much the rest of the nervous system is "attuned" to being connected to a specific brain and vice versa. That is, even if the brainstem could be 100% connected to the spinal cord, we don't know how hard it would be to adapt to the new body. Could it result in something resembling the alien hand syndrome [1] or body integrity identity disorder [2], for instance?

[1] http://en.wikipedia.org/wiki/Alien_hand_syndrome

[2] http://en.wikipedia.org/wiki/Body_integrity_identity_disorde...

well, I don't really think this is the case, not for metaphysical reason or such, but because glands and the chemicals they produce have a high impact on how the brain functions

http://www.jabfm.org/content/23/5/677.full

I'd argue that the completely different chemical balance the brain will be subject to will cause dramatic behavioral swings, even if the patient memory and skills might be maintained (well, not the motor skill, I guess)

How do you know that we can swap everything else and the person will still be the same person?

Because we've done it.

OK, that's a bit facetious. A combination of existing transplantation procedures (heart? check. liver? check. kidneys? check...) and the fact that sometimes people need things removed but not replaced (thyroid, for example) leaves nothing but the brain as the organ which can't be removed and/or replaced without changing who the person is.

There's quite a big gap between "some bits have been removed or replaced" and "the brain is the only bit that can't be replaced" without changing who the person is.

The nervous system (of which the brain is but a part) is quite a large and complex thing, and there is no guarantee that one's conscious being is tied to that set of neurons in one's head and not, for example, to the extended set below the neck. There's evidence that certain functions are performed mostly or wholly within the brain, but no evidence of consciousness, which is what I think you mean by "changing who the person is".

Heart? Liver? Kidneys? Thyroid and appendix and gallbladders? They ain't got nothin' on the nervous system when it comes to me.

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