One of the simplest known organisms, the worm C. Elegans, has a brain consisting of 302 neurons that we have mapped exactly. (The entire thing is 959 cells.) We still can't simulate it correctly.
A rat's brain is O(10^7) neurons, while a human brain is O(10^11) neurons, as compared to C. Elegans with O(10^2) neurons.
Which is to say, trying to simulate a rat brain while we know we can't simulate C. Elegans is like a prehistoric human claiming he can build an F1 racecar before he's invented the wheel.
