You could try looking at existing animal neural counts: https://en.wikipedia.org/wiki/List_of_animals_by_number_of_n... Doublings or 20xing get you a long way: a 1/20x cerebral cortex neural count decrease takes you from human to... horse. I like horses a lot, but there's clearly a very wide gulf in capabilities, and I don't like the thought of ever encountering someone who is to us as we are to horses.