[PatrickHenry]

This "gradual-replacement-of-brain-cells-with-chips" scenario is a restated version of an ancient philosophical problem: Theseus' Ship.

[RightWhale]

Sounds like my '86 Caprice. Of course, gasoline is part of the car that is replaced at [very] frequent intervals. But if we run out of gasoline altogether, would we be a nation of 500 million cars any longer? Would these piles of plastic and thin steel panels be cars if there were no gasoline?

[js1138]

Everything about our personalities, including our consciousness and our ability to experience pleasure and pain, functions to preserve and replicate a package of DNA.

Prosthetic brain cells will need to emulate all aspects of that functionality.

[Physicist]

Theseus's Ship is the problem exactly, except that we are facing it now. There is a constant turnover of cells in every body, and a constant turnover of atoms in every cell. None of us is made of the same stuff we were made of a year ago.

[Junior]

I remember visiting HMS Victory back in '90. The docent (a Royal Navy sailor) explained that only about 25 percent of the ship dated from the battle of Trafalgar as the various timbers had been replaced over the years.

[VadeRetro]

Theseus's ship is an unnecessarily complicated version of George Washington's axe. You hold up a traditional wooden-handled axe and announce: "This is George Washington's original axe that cut down the cherry tree! The very one! It's had twelve new handles and three new heads since then, of course."