Lots of interesting stuff and links in this article, way too much to post here.

Your brain might be a quantum computer that hallucinates math
There's a code for arithmetic hidden inside your head

... When you perform a simple math function, such as adding two plus two, your brain may hallucinate all of the possible answers at once while simultaneously working to both remember the answer (you’ve definitely added those numbers before) and to process the data (1+1+1+1).

If the human brain were binary, you’d probably have to wait for it to go through each permutation individually instead of hallucinating them all at once.