Basically impossible impossibility. For a system which derives its behavior from complex interactions between those billion components, you can only understand its origins how it was tuned, and some high-level concepts of its workings. (Which we already achieved both for human brain and ANN).
Not sure what the neuroscientists are even researching at this point, has there been any major findings from neuroscience in the last 10 years? (With similar kind of impact as Transformers in 2017?)