The point is that it's pretty clearly a visual area above all else. The pathway from the eye to V1 is possibly the most extensively studied functional neuroanatomical pathway in the brain.

It's also well-established that it takes input from other regions and that this adjusts visual percepts. The idea that mathematical operations recruit visual areas is unsurprising and predicted by every theory of numerical cognition there is. That's why this is interesting.

I'm sorry, but what you're claiming is patently absurd (and, I suspect, purely contrarian).

This is perhaps a poor backup claim because I can't give a relevant citation, but back when I was in Neuroscience / neuroanatomy in medical school, I remember feeling deeply impressed at the level to which we do understand the visual processing system in the brain. Its far more comprehensive than simple imaging studies -- we know where the wires go, how the photons are transduced and turned into patterns of neurons firing, etc. There's of course plenty to learn but our depth of understanding in regards to human vision is impressive.

Yes, we're working on writing it and will let you know.