[1] https://en.wikipedia.org/wiki/Grandmother_cell
[2] https://www.youtube.com/playlist?list=PL8FnQMH2k7jzPrxqdYufo...
Firstly even if there is such a cell that only fires for one face, or perhaps also the person’s name, it doesn’t mean there aren’t other cells that fire for that person, or for people in general including that person. Without those as well, that neurons responses might not mean anything to the rest if the brain. It’s a though experiment but never really demonstrated.
Also even if this is true in the very strongest sense. Say there is one neuron that uniquely and discretely fires in response to thinking about that one person. What defines a neuron isn’t just its internal behaviour. It’s also the pattern of inputs that influence it, and the pattern of outputs it sends out. It’s the connections and dependencies on the weightings and signals and responses from all the cells it’s connected to. Including the specific unique ways all those neurons are connected, or not connected to all the other cells in the brain, that what make the behaviour of that neuron meaningful.
If you took that neuron an implanted it into another brain, you’d need to hook it up to the neurons in that brain such that it gets exactly the same stimuli, in the same order, with the same strength, every time it needs to fire. The same applies to its output, al, the neurons it’s connected to would have to interpret its firing behaviour in the exact same way the other neurons in the original brain did. But there’s no guarantee any of those connected mechanisms work or are physically connected in the same way, or even a vaguely similar or compatible way in the new brain.
So you can’t extract the weightings for ‘an’ discretely because those weightings encode its connection with all the other words and combinations and sequences or clusters of words it might ever be used with, including their weightings with other preceding words, and their relationships, etc, etc.