I'm no expert at all on neuroscience, but when I recently got the opportunity to read a transcript of the lecture titled The Value of Science by Richard Feynman, it filled me with awe and reverence. I can't but share a sizable quote from the same.
“For instance, the scientific article may say, 'The radioactive phosphorus content of the cerebrum of the rat decreases to one- half in a period of two weeks.' Now what does that mean? It means that phosphorus that is in the brain of a rat—and also in mine, and yours—is not the same phosphorus as it was two weeks ago. It means the atoms that are in the brain are being replaced: the ones that were there before have gone away. So what is this mind of ours: what are these atoms with consciousness? Last week's potatoes! They now can remember what was going on in my mind a year ago—a mind which has long ago been replaced. To note that the thing I call my individuality is only a pattern or dance, that is what it means when one discovers how long it takes for the atoms of the brain to be replaced by other atoms. The atoms come into my brain, dance a dance, and then go out—there are always new atoms, but always doing the same dance, remembering what the dance was yesterday.”
I recall some debate around the oldest buildings, and how (I think) the Ise Grand Shrine [1] is disqualified because it is rebuilt regularly -- for the past 2000 years. Of course, one may resolve this by more carefully defining "oldest building", but this quote by Feynman makes me lean towards a definition that includes this shrine. Who are we to say that some building is different because the atoms of its beams came from different trees, and in the same breath claim individual continuity across decades in the face of this fact about our brain?
https://calteches.library.caltech.edu/1575/1/Science.pdf
“For instance, the scientific article may say, 'The radioactive phosphorus content of the cerebrum of the rat decreases to one- half in a period of two weeks.' Now what does that mean? It means that phosphorus that is in the brain of a rat—and also in mine, and yours—is not the same phosphorus as it was two weeks ago. It means the atoms that are in the brain are being replaced: the ones that were there before have gone away. So what is this mind of ours: what are these atoms with consciousness? Last week's potatoes! They now can remember what was going on in my mind a year ago—a mind which has long ago been replaced. To note that the thing I call my individuality is only a pattern or dance, that is what it means when one discovers how long it takes for the atoms of the brain to be replaced by other atoms. The atoms come into my brain, dance a dance, and then go out—there are always new atoms, but always doing the same dance, remembering what the dance was yesterday.”