Could you clarify what you mean by operate on? Or is that part of the point?

Using the definition of 'operate on' that I think is most natural, I'd say there is a .05% chance that these functions only operate on (effect) the physical brain. Unless you mean directly, and then I would assign an 80% chance.

Using the definition of 'operating on' meaning 'requiring', I'd say that there is a 90% chance (probability) that only the brain is required for 90% (fraction) of its functioning. The probabilities I assign would fall down dramatically as you try to raise the 2nd 90% (the fraction). So that I would probably only assign a 1% chance that 100% of higher functions require only the brain.