[apl]

We didn't have to reverse-engineer the CPU. Also, CPUs are rationally designed; we have zero guarantees that an evolved brain follows any principles at all. Every brain region may be highly specialised to a single algorithm or task with zero mechanistic overlap. Figuring out deep neural nets is a closer analogy, and at the moment we have very little intuition for how to do even that. Keep in mind that the brain is vastly more complex than even the most advanced ANNs.

On the technical side: The most advanced neural techniques allow for parallel measurement calcium signals in ~10,000 neurones. That's a long way off from complete observation!