We know people can have only 50% of a full brain and yet be conscious, and we also know that destruction of a few tiny pieces of the brain can result in a loss of consciousness in the sense we mean it here. The commonality is that neuron systems are required; individual neurons are not enough, nor is an entire intact animal brain without certain structures.
The line is arbitrary, but it doesn't matter so much. The factual reality is that neuron systems are what we can currently (currently! this may change) prove gives rise to consciousness, regardless of philosophical attempts at violence against the science.
Sorry but thats actually wrong.
Read this:
This merely supports my hypothesis that neuron systems are what is needed... you will notice nobody is claiming that there are conscious people with 0% brain matter remaining.
You wrote this:
"We know people can have only 50% of a full brain"
And so the question is how you define a full brain.
Neuron systems are network. It might as well be that a network is needed not the neurons per se.
You are making an arbitrary choice here - why the neurons? Why not the whole brain? Some structure within the brain? The molecules making up the neurons?