I have not studied Buddhist theory in many years, not since a class at Cal with Frits Staal, but one relatively clear recollection is that it is in some respects atomistic, in that time, space, and self are seen as discontinuous. They are so many beads, called dharmas (dharma has a lot of meanings).
It just struck me that what most likely is “extinguished” in Nirvana (which means to extinguish or snuff out, like a candle) is the habit of continually renewing the same perceptual structures. That structure builder, which we might usefully call the ego, simply lets things be.
What caused me to think this was a neurofeedback session I just did, in which I noticed the quality of my tinnitus altered slightly. It has never done that, to my recollection. And it hit me that some part of my neurological and perceptual apparatus would want to immediately return it to the status quo ante, even though it is mildly unpleasant.
Why would some unconscious part of me do that? Because building castles in the air is what it does.
I think this is a beginning of a good approximation.