what makes you, you ?
we tend to intuitively think of a person as their entire body, somehow including limbs and organs but not clothing or food.
yet, if you close your eyes, and then i swap your arm with someone else's, when you wake up you will still be the same person, just with a new arm. in fact, i'd argue i could replace everything except for the nervous system (including the brain) and when you open your eyes again you would notice that your entire body has changed but your thoughts and memories have remained the same — rather than, for example, still having the same body but different thoughts and memories.
are you the matter that makes up that nervous system ? i could probably replace neurons and synapses one at a time and you would continue to be the same person. is it the electric signals then ? i could probably put on some synapses a device that absorbs electric signals and then sends out identical but "different" signals and you would still be the same person.
in fact, it doesn't really make sense to ask "which matter" makes up your nervous system: under quantum physics, everything is changing and particles are merely values in an omnipresent field rather than solid objects.
ultimately, what you are, is the information system which your nervous system (including your brain) runs. standing still, walking forwards, teleporting yourself, and being uploaded into a sufficiently powerful computer, all preserve your personhood in the exact same way; there is nothing special about the meat that currently runs your mind.
despite everything, it's still you.