This is one of those complex topics that we don’t truly understand well yet
We’ve called them a distributed intelligence, because they do basically have a core brain and auxillary brains - but is there really any other kind?
It seems to be to be something like their core brain is in control, and the auxiliary brains are a combination motor cortex/occipital lobe (vision is our primary sense, but even though their eyes are better they have taste+smell+touch+em sense? All over their tentacles).
Conversely, we also have a brain worth of neurons in our gut and a lot of capacity to learn reactions at the spinal cord. Our brains could also be described as several brains clumped together… Personally, my fingers know a ton of things I don’t know consciously.
We also have the capacity to “run” two human level intelligences - server the link between the hemispheres and you can get an auxiliary person who can have different opinions, understand language independently, and even communicate separately through writing
We really don’t know how brains work, they’re black boxes to us. We know that “if I destroy this region, it will impact that capability”, but in a more fundamental sense? We’ve barely scratched the surface